Vol. 77 Wednesday, No. 100 May 23, 2012

Part III

Department of Transportation

National Highway Traffic Safety Administration 49 CFR Part 571 Federal Motor Vehicle Safety Standards; Electronic Stability Control Systems for Heavy Vehicles; Proposed Rule

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DEPARTMENT OF TRANSPORTATION New Jersey Avenue SE., West Building A. UMTRI Study Ground Floor, Room W12–140, B. Simulator Study National Highway Traffic Safety Washington, DC 20590–0001 C. NHTSA Track Testing Administration • Hand Delivery or Courier: West 1. Effects of Stability Control Systems— Phase I Building Ground Floor, Room W12–140, 49 CFR Part 571 2. Developing a Dynamic Test Maneuver 1200 New Jersey Avenue SE., between and Performance Measure To Evaluate [Docket No. NHTSA–2012–0065] 9 a.m. and 5 p.m. ET, Monday through Roll Stability—Phase II Friday, except Federal holidays. (a) Test Maneuver Development RIN 2127–AK97 • Fax: (202) 493–2251 (b) Performance Measure Development Instructions: For detailed instructions 3. Developing a Dynamic Test Maneuver Federal Motor Vehicle Safety on submitting comments and additional and Performance Measure To Evaluate Standards; Electronic Stability Control information on the rulemaking process, Yaw Stability—Phase III Systems for Heavy Vehicles see the Public Participation heading of (a) Test Maneuver Development (b) Performance Measure Development the SUPPLEMENTARY INFORMATION AGENCY: National Highway Traffic section 4. Large Bus Testing Safety Administration (NHTSA), of this document. Note that all D. Truck & Engine Manufacturers Department of Transportation (DOT). comments received will be posted Association Testing ACTION: Notice of proposed rulemaking without change to http:// 1. Slowly Increasing Steer Maneuver (NPRM). www.regulations.gov, including any 2. Ramp Steer Maneuver personal information provided. Please 3. Sine With Dwell Maneuver SUMMARY: This document proposes to see the Privacy Act heading below. 4. Ramp With Dwell Maneuver establish a new Federal Motor Vehicle Privacy Act: Anyone is able to search 5. Vehicle J Testing Safety Standard No. 136 to require the electronic form of all comments (a) EMA Testing of Vehicle J electronic stability control (ESC) received into any of our dockets by the (b) NHTSA Testing of EMA’s Vehicle J E. Other Industry Research systems on truck tractors and certain name of the individual submitting the 1. Decreasing Radius Test buses with a gross vehicle weight rating comment (or signing the comment, if 2. Lane Change on a Large Diameter Circle of greater than 11,793 kilograms (26,000 submitted on behalf of an association, 3. Yaw Control Tests pounds). ESC systems in truck tractors business, labor union, etc.). You may V. Agency Proposal and large buses are designed to reduce review DOT’s complete Privacy Act A. NHTSA’s Statutory Authority untripped rollovers and mitigate severe Statement in the Federal Register B. Applicability understeer or oversteer conditions that published on April 11, 2000 (65 FR 1. Vehicle Types lead to loss of control by using 19477–78). 2. Retrofitting In-Service Truck Tractors, automatic computer-controlled braking Docket: For access to the docket to Trailers, and Buses 3. Exclusions From Stability Control and reducing engine torque output. read background documents or In 2012, we expect that about 26 Requirement comments received, go to http:// C. ESC System Capabilities percent of new truck tractors and 80 www.regulations.gov. Follow the online 1. Choosing ESC vs. RSC percent of new buses affected by this instructions for accessing the dockets. 2. Definition of ESC proposed rule will be equipped with FOR FURTHER INFORMATION CONTACT: For D. ESC Disablement ESC systems. We believe that ESC technical issues, you may contact E. ESC Malfunction Detection, Telltale, and systems could prevent 40 to 56 percent George Soodoo, Office of Crash Activation Indicator of untripped rollover crashes and 14 Avoidance Standards, by telephone at 1. ESC Malfunction Detection 2. ESC Malfunction Telltale percent of loss-of-control crashes. By (202) 366–4931, and by fax at (202) 366– requiring that ESC systems be installed 3. ESC Activation Indicator 7002. For legal issues, you may contact F. Performance Requirements and on truck tractors and large buses, this David Jasinski, Office of the Chief proposal would prevent 1,807 to 2,329 Compliance Testing Counsel, by telephone at (202) 366– 1. Characterization Test—SIS crashes, 649 to 858 injuries, and 49 to 2992, and by fax at (202) 366–3820. You 2. Roll and Yaw Stability Test—SWD 60 fatalities at less than $3 million per may send mail to both of these officials (a) Roll Stability Performance equivalent life saved, while generating at the National Highway Traffic Safety (b) Yaw Stability Performance positive net benefits. Administration, 1200 New Jersey (c) Lateral Displacement DATES: Comments: Submit comments on Avenue SE., Washington, DC 20590. 3. Alternative Test Maneuvers Considered or before August 21, 2012. (a) Characterization Maneuver SUPPLEMENTARY INFORMATION: Public Hearing: NHTSA will hold a (b) Roll Stability Test Maneuvers public hearing in the summer of 2012. Table of Contents (c) Yaw Stability Test Maneuvers NHTSA will announce the date for the (d) Lack of an Understeer Test I. Executive Summary 4. ESC Malfunction Test hearing in a supplemental Federal II. Safety Problem 5. Test Instrumentation and Equipment Register document. The agency will A. Heavy Vehicle Crash Problem (a) Outriggers accept comments to the rulemaking at B. Contributing Factors in Rollover and (b) Automated Steering Machine this hearing. Loss-of-Control Crashes (c) Anti-Jackknife Cables ADDRESSES: You may submit comments C. NTSB Safety Recommendations (d) Control Trailer electronically [identified by DOT Docket D. Motorcoach Safety Plan (e) Sensors Number NHTSA–2012–0065] by visiting E. International Regulation 6. Test Conditions the following Web site III. Stability Control Technologies (a) Ambient Conditions • Federal eRulemaking Portal: Go to A. Dynamics of a Rollover (b) Road Test Surface http://www.regulations.gov. Follow the B. Description of RSC System Functions (c) Vehicle Test Weight C. Description of ESC System Functions (d) Tires online instructions for submitting D. How ESC Prevents Loss of Control (e) Mass Estimation Drive Cycle comments. E. Situations in Which Stability Control (f) Brake Conditioning Alternatively, you can file comments Systems May Not Be Effective 7. Data Filtering and Post Processing using the following methods: F. Difference in Vehicle Dynamics Between G. Compliance Dates and Implementation • Mail: Docket Management Facility: Light Vehicles and Heavy Vehicles Schedule U.S. Department of Transportation, 1200 IV. Research and Testing VI. Benefits and Costs

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A. System Effectiveness collision. Based on the agency’s the agency was able to develop reliable B. Target Crash Population estimates regarding the effectiveness of and repeatable test maneuvers that C. Benefits Estimate ESC systems, we believe that an ESC could demonstrate a stability control D. Cost Estimate E. Cost Effectiveness standard could annually prevent 1,807 system’s ability to prevent rollover and F. Comparison of Regulatory Alternatives to 2,329 crashes, 649 to 858 injuries, loss of directional control among the VII. Public Participation and 49 to 60 fatalities, while providing varied configurations of truck tractors VIII. Regulatory Analyses and Notices net economic benefits. and buses in the fleet. A. Executive Order 12866, Executive Order There have been two types of stability In order to realize these benefits, the 13563, and DOT Regulatory Policies and control systems developed for heavy agency is proposing to require new Procedures vehicles. A roll stability control (RSC) truck tractors and certain buses with a B. Regulatory Flexibility Act system is designed to prevent rollover C. Executive Order 13132 (Federalism) GVWR of greater than 11,793 kilograms D. Executive Order 12988 (Civil Justice by decelerating the vehicle using (26,000 pounds) to be equipped with an Reform) braking and engine torque control. The ESC system. This proposal is made E. Protection of Children From other type of stability control system is pursuant to the authority granted to Environmental Health and Safety Risks ESC, which includes all of the functions NHTSA under the National Traffic and F. Paperwork Reduction Act of an RSC system plus the ability to Motor Vehicle Safety Act (‘‘Motor G. National Technology Transfer and mitigate severe oversteer or understeer Vehicle Safety Act’’). Under 49 U.S.C. Advancement Act by automatically applying brake force at Chapter 301, Motor Vehicle Safety (49 H. Unfunded Mandates Reform Act selected wheel-ends to help maintain I. National Environmental Policy Act U.S.C. 30101 et seq.), the Secretary of J. Plain Language directional control of a vehicle. To date, Transportation is responsible for K. Regulatory Identifier Number (RIN) ESC and RSC systems for heavy vehicles prescribing motor vehicle safety L. Privacy Act have been developed for air-braked standards that are practicable, meet the vehicles. Truck tractors and buses need for motor vehicle safety, and are I. Executive Summary covered by this proposed rule make up stated in objective terms. The The agency proposes to reduce a large proportion of air-braked heavy responsibility for promulgation of rollover and loss of directional control vehicles and a large proportion of the Federal motor vehicle safety standards of truck tractors and large buses by heavy vehicles involved in both rollover is delegated to NHTSA. establishing a new standard, Federal crashes and total crashes. Based on This proposal requires ESC system Motor Vehicle Safety Standard (FMVSS) information we have received to date, must meet both definitional criteria and No. 136, Electronic Stability Control the agency has tentatively determined performance requirements. It is Systems for Heavy Vehicles. The that ESC and RSC systems are not necessary to include definitional criteria standard would require truck tractors available for hydraulic-braked medium in the proposal and require compliance and certain buses 1 with a gross vehicle or heavy vehicles. with them because developing separate weight rating (GVWR) of greater than Since 2006, the agency has been performance tests to cover the wide 11,793 kilograms (26,000 pounds) to be involved in testing truck tractors and array of possible operating ranges, equipped with an electronic stability large buses with stability control roadways, and environmental control (ESC) system that meets the systems. To evaluate these systems, conditions would be impractical. The equipment and performance criteria of NHTSA sponsored studies of crash data definitional criteria are consistent with the standard. ESC systems use engine in order to examine the potential safety those recommended by SAE torque control and computer-controlled benefits of stability control systems. International and used by the United braking of individual wheels to assist NHTSA and industry representatives Nations (UN) Economic Commission for the driver in maintaining control of the separately evaluated data on dynamic Europe (ECE), and similar to the vehicle and maintaining its heading in test maneuvers. At the same time, the definition of ESC in FMVSS No. 126, situations in which the vehicle is agency launched a three-phase testing the agency’s stability control standard becoming roll unstable (i.e., wheel lift program to improve its understanding of for light vehicles. This definition would potentially leading to rollover) or how stability control systems in truck describe an ESC system as one that experiencing loss of control (i.e., tractors and buses work and to develop would enhance the roll and yaw deviation from driver’s intended path dynamic test maneuvers to challenge stability of a vehicle using a computer- due to understeer, oversteer, trailer roll propensity and yaw stability. By controlled system that can receive swing or any other yaw motion leading combining the studies of the crash data inputs such as the vehicle’s lateral to directional loss of control). In such with the testing data, the agency is able acceleration and yaw rate, and use the situations, intervention by the ESC to evaluate the potential effectiveness of information to apply brakes system can assist the driver in stability control systems for truck individually, including trailer brakes, maintaining control of the vehicle, tractors and large buses. and modulate engine torque. thereby preventing fatalities and injuries As a result of the data analysis The proposal requires that the system associated with vehicle rollover or research, we have tentatively be able to detect a malfunction and determined that ESC systems can be 28 provide a driver with notification of a 1 As explained later in this notice, the to 36 percent effective in reducing first- malfunction by means of a telltale. This applicability of this proposed standard to buses event untripped rollovers and 14 would be similar to the applicability of NHTSA’s requirement would be similar to the proposal to require seat belts on certain buses. percent effective in eliminating loss-of- malfunction detection and telltale These buses would have 16 or more designated control crashes caused by severe requirements for light vehicles in 2 seating positions (including the driver), at least 2 oversteer or understeer conditions. As FMVSS No. 126. An ESC system on/off rows of passenger seats that are rearward of the a result of the agency’s testing program driver’s seating position and forward-facing or can switch is allowed for light vehicles; convert to forward-facing without the use of tools. and the test data received from industry, however, there is no provision in this As with the seat belt NPRM, this proposed rule proposal for allowing an ESC system to would exclude school buses and urban transit buses 2 See Wang, Jing-Shiam, ‘‘Effectiveness of sold for operation as a common carrier in urban Stability Control Systems for Truck Tractors’’ be deactivated. For truck tractors and transportation along a fixed route with frequent (January 2011) (DOT HS 811 437); Docket No. large buses, we do not believe such stops. NHTSA–2010–0034–0043. controls are necessary.

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After considering and evaluating respectively. These two metrics can from suppliers of these systems and to several test maneuvers, the agency is effectively measure what NHTSA’s complete necessary engineering on all proposing to use two test maneuvers for testing has found to be the threshold of vehicles. For three-axle tractors with performance testing: The slowly stability. The lateral displacement one drive axle, tractors with four or increasing steer (SIS) maneuver and the metric would be used to ensure that the more axles, and severe service tractors, sine with dwell (SWD) maneuver. The stability control system is not set to we would provide two years additional SIS maneuver is a characterization intervene solely by making the vehicle lead time. We believe this additional maneuver used to determine the nonresponsive to driver input. The time is necessary to develop, test, and relationship between a vehicle’s steering engine torque reduction metric would equip these vehicles with ESC systems. wheel angle and the lateral acceleration. be used to ensure that the system has Although the agency has statutory This test serves both to normalize the the capability to automatically reduce authority to require retrofitting of in- severity of the SWD maneuver and to engine torque in response to high lateral service truck tractors, trailers, and large ensure that the system has the ability to acceleration and yaw rate conditions. buses, the agency is not proposing to do reduce engine torque. The SIS maneuver The manner in which the data would be so, given the integrated aspects of a is performed by driving at a constant filtered and processed is described in stability control system. speed of 48 km/h (30 mph), and then this proposal. increasing the steering wheel angle at a The agency considered several test Based on the agency’s effectiveness constant rate of 13.5 degrees per second maneuvers based on its own work and estimates, the adoption of this proposal until ESC system activation occurs. that of industry. In particular, the would prevent 1,807 to 2,329 crashes Using linear regression followed by agency’s initial research focused on a per year resulting in 649 to 858 injuries extrapolation, the steering wheel angle ramp steer maneuver (RSM) for and 49 to 60 fatalities. The proposal also that would produce a lateral evaluating roll stability. In that would result in significant monetary acceleration of 0.5g is determined. maneuver, a vehicle is driven at a savings as a result of prevention of Using the steering wheel angle constant speed and a steering wheel property damage and travel delays. derived from the SIS maneuver, the input that is based on the steering wheel Based on information obtained from agency would conduct the sine with angle derived from the SIS maneuver is manufacturers, the agency estimates that dwell maneuver. The SWD test input. The steering wheel angle is then 26.2 percent of truck tractors maneuver challenges both roll and yaw held for a period of time before it is manufactured in model year 2012 will stability by subjecting the vehicle to a returned to zero. A stability control be equipped with an ESC system and sinusoidal input. To conduct the SWD system would act to reduce lateral that 80 percent of covered buses maneuver, the vehicle is accelerated to acceleration, and thereby wheel lift and manufactured in model year 2012 will 72 km/h (45 mph) and then turned in a roll instability, by applying selective be equipped with an ESC system. clockwise or counterclockwise direction braking. A vehicle without a stability Information obtained from to reach a set steering wheel angle in 0.5 control system would maintain high manufacturers indicates that the average seconds. The steering wheel is then levels of lateral acceleration and unit cost of an ESC system is turned in the opposite direction until potentially experience wheel lift or approximately $1,160. In addition, 16.5 the same steering wheel angle is reached rollover. percent of truck tractors manufactured The proposed rule also sets forth the in the opposite direction in one second. in model year 2012 will be equipped test conditions that the agency would The steering wheel is then held at that with an RSC system. The incremental steering wheel angle for one second, and use to ensure safety and demonstrate cost of installing an ESC system in place then the steering wheel angle returned sufficient performance. All vehicles of an RSC system is estimated to be to zero degrees within 0.5 seconds. This would be tested using outriggers for the $520 per vehicle. Based upon the maneuver would be repeated for two safety of the test driver. The agency agency’s estimates that 150,000 truck series of test runs (first in the would use an automated steering tractors and 2,200 buses covered by this counterclockwise direction and then in controller to ensure reproducible and proposed rule will be manufactured in the clockwise direction) at several target repeatable test execution performance. 2012, the agency estimates that the total steering wheel angles from 30 to 130 Truck tractors would be tested with an cost of this proposal would be percent of the angle derived in the SIS unbraked control trailer to eliminate the approximately $113.6 million. maneuver. effect of the trailer’s brakes on testing. The lateral acceleration, yaw rate, and Because the agency tests new vehicles, The agency believes that this proposal engine torque data from the test runs the brakes would be conditioned, as is cost effective. The net benefits of this would be measured, recorded, and they are in determining compliance proposal are estimated to range from processed to determine the four with the air brake standard. The agency $228 to $310 million at a 3 percent performance metrics: Lateral would also test to ensure that system discount rate and from $155 to $222 acceleration ratio (LAR), yaw rate ratio malfunction is detected. million at a 7 percent discount rate. As (YRR), lateral displacement, and engine This proposed rule would take effect a result, the net cost per equivalent live torque reduction. The LAR and YRR for most truck tractors and covered saved from this proposal ranges from metrics would be used to ensure that the buses produced two years after $1.5 to $2.0 million at a 3 percent system reduces lateral acceleration and publication of a final rule. We believe discount rate and from $2.0 to $2.6 yaw rate, respectively, after an that this amount of lead time is million at a 7 percent discount rate. The aggressive steering input, thereby necessary to ensure sufficient costs and benefits of this proposal are preventing rollover and loss of control, availability of stability control systems summarized in Table 1.

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TABLE 1—ESTIMATED ANNUAL COST, BENEFITS, AND NET BENEFITS OF THE PROPOSAL [In millions of 2010 dollars]

Property damage Cost per Costs Injury benefits and travel delay equivalent live Net benefits savings saved

At 3% Discount ...... $113.6 $328–405 $13.9–17.8 $1.5–2.0 $228–310 At 7% Discount ...... 113.6 257–322 11.0–14.1 2.0–2.6 155–222

The agency considered two regulatory Combination vehicles represent about and 40 percent, respectively, of all buses alternatives. First, the agency 25 percent of large trucks registered but involved in fatal crashes. Most of the considered requiring truck tractors and travel 63 percent of the large truck transit bus and school bus crashes are large buses to be equipped with RSC miles, annually. Traffic tie-ups resulting not rollover or loss-of-control crashes systems. When compared to this from loss-of-control and rollover crashes that ESC systems are capable of proposal, RSC systems would result in also contribute to in millions of dollars preventing. The remaining 13 percent of slightly lower cost per equivalent life of lost productivity and excess energy buses involved in fatal crashes were saved, but would produce net benefits consumption each year. classified as other buses or unknown. According to Traffic Safety Facts that are lower than the net benefits from Fatal rollover and loss-of-control 2009, the overall crash problem for this proposal. This is because RSC crashes are a subset of these crashes. systems are less effective at preventing tractor trailer combination vehicles is rollover crashes and much less effective approximately 150,000 crashes, 29,000 There are many more fatalities in at preventing loss-of-control crashes. of which involve injury. The overall buses with a GVWR greater than 11,793 The second alterative considered was crash problem for single-unit trucks is kg (26,000 lb) compared to buses with requiring trailers to be equipped with nearly as large—approximately 146,000 a GVWR between 4,536 kg and 11,793 RSC systems. However, this alternative crashes, 24,000 of which are injury kg (10,000 lb and 26,000 lb).5 In the would save fewer than 10 lives at a very crashes. However, the fatal crash 10-year period between 1999 and 2008, high cost per equivalent life saved and involvement for truck tractors is much there were 34 fatalities on buses with a would provide negative net benefits. higher. In 2009, there were 2,334 fatal GVWR between 4,536 kg and 11,793 kg The remainder of this notice will combination truck crashes and 881 fatal (10,000 lb and 26,000 lb) compared to describe in detail the following: (1) The single-unit truck crashes. 254 fatalities on buses with a GVWR size of the safety problem to be The rollover crash problem for greater than 11,793 kg (26,000 lb). addressed by this proposed rule; (2) combination trucks is much greater than Among buses with a GVWR of greater for single-unit trucks. In 2009, there how stability control systems work to than 11,793 kg (26,000 lb), over 70 were approximately 7,000 crashes prevent rollover and loss of control; (3) percent of the fatalities were cross- the research and testing separately involving combination truck rollover country intercity bus occupants. conducted by NHTSA and industry to and 3,000 crashes involving single-unit evaluate the potential effectiveness of a truck rollover. As a percentage of all Furthermore, the size of the rollover stability control requirement and to crashes, combination trucks are crash problem for cross-country develop dynamic test maneuvers to involved in rollover crashes at twice the intercity buses is greater than in other challenge system performance; (4) the rate of single-unit trucks. buses. According to FARS data from specifics of the agency’s proposal, Approximately 4.4 percent of all 1999 to 2008, there were 97 occupant including equipment and performance combination truck crashes were fatalities as a result of rollover events on criteria, compliance testing, and the rollovers, but 2.2 percent of single-unit cross-country intercity buses with a implementation schedule; and (5) the truck crashes were rollovers. GVWR of greater than 11,793 kg (26,000 benefits and costs of this proposal. Combination trucks were involved in lb), which represents 52 percent of 3,000 injury crashes and 268 fatal 6 II. Safety Problem cross-country intercity bus fatalities. In crashes, and single-unit trucks were comparison, rollover crashes were A. Heavy Vehicle Crash Problem involved in 2,000 injury crashes and responsible for 21 occupant fatalities on The Traffic Safety Facts 2009 reports 154 fatal crashes. other buses with a GVWR of greater than that tractor trailer combination vehicles According to FMCSA’s Large Truck 11,793 kg (26,000 lb) and 9 occupant are involved in about 72 percent of the and Bus Crash Facts 2008, cross-country fatalities on all buses with a GVWR fatal crashes involving large trucks, intercity buses were involved in 19 of between 4,536 kg and 11,793 kg (10,000 the 247 fatal bus crashes in 2008, which annually.3 According to FMCSA’s Large lb and 26,000 lb). That is, 95 percent of represented about 0.5 percent of the Truck and Bus Crash Facts 2008, these bus occupant rollover fatalities on buses fatal crashes involving large trucks and vehicles had a fatal crash involvement over 4,536 kg (10,000 lb) were rate of 1.92 crashes per 100 million buses, annually. The bus types presented in the crash data include occupants on buses with a GVWR of vehicle miles traveled during 2007, over 11,793 kg (26,000 lb). whereas single unit trucks had a fatal school buses, intercity buses, cross- crash involvement rate of 1.26 crashes country buses, transit buses, and other 5 This data was taken from the FARS database 4 buses. These buses had a fatal crash per 100 million vehicle miles traveled. and was presented in the NPRM that would require involvement rate of 3.47 crashes per 100 seat belts on certain buses. See 75 FR 50,958, 50,917 3 DOT HS 811 402, available at http://www- million vehicle miles traveled during (Aug. 18, 2010). nrd.nhtsa.dot.gov/Pubs/811402.pdf (last accessed 2008. From 1998 to 2008, cross-country 6 See U.S. Department of Transportation May 9, 2012). intercity buses, on average, accounted Motorcoach Safety Action Plan, DOT HS 811 177, 4 FMCSA–RRA–10–043 (Mar. 2010), available at for 12 percent of all buses involved in at 13 (Nov. 2009), available at http:// http://www.fmcsa.dot.gov/facts-research/ltbcf2008/ www.fmcsa.dot.gov/documents/safety-security/ index-2008largetruckandbuscrashfacts.aspx (last fatal crashes, whereas transit buses and MotorcoachSafetyActionPlan_finalreport-508.pdf accessed May 9, 2012). school buses accounted for 35 percent (last accessed May 9, 2012).

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B. Contributing Factors in Rollover and On a dry, high-friction asphalt or • H–11–08: Once the performance Loss-of-Control Crashes concrete surface, a tractor trailer standards from Safety Recommendation Many factors related to heavy vehicle combination vehicle executing a severe H–11–07 have been developed, require operation, as well as factors related to turning maneuver is likely to experience the installation of stability control roadway design and road surface a high lateral acceleration, which may systems on all newly manufactured properties, can cause heavy vehicles to lead to roll or yaw instability. A similar commercial vehicles with a GVWR become yaw unstable or to roll. Listed maneuver performed on a wet or greater than 10,000 pounds. below are several real-world situations slippery road surface is not as likely to D. Motorcoach Safety Plan in which stability control systems may experience the high lateral acceleration because of less available tire traction. In November 2009, the U.S. prevent or lessen the severity of such Department of Transportation crashes. Hence, the result is more likely to be • vehicle yaw instability than vehicle roll Motorcoach Safety Action Plan was Speed too high to negotiate a issued.8 Among other things, the curve—The entry speed of vehicle is too instability. • Road design configuration—Some Motorcoach Safety Action Plan includes high to safely negotiate a curve. When an action item for NHTSA to assess the the lateral acceleration of a vehicle drivers may misjudge the curvature of ramps and not brake sufficiently to safety benefits for stability control on during a steering maneuver exceeds the large buses and develop objective vehicle’s roll or yaw stability threshold, negotiate the curve safely. This includes ramps with decreasing radius curves as performance standards for these a rollover or loss of control is initiated. systems.9 Consistent with that plan, Curves can present both roll and yaw well as curves and ramps with improper signage. A decrease in super-elevation NHTSA made a decision to pursue a instability issues to these types of stability control requirement for large vehicles due to varying heights of loads (banking) at the end of a ramp where it merges with the roadway causes an buses. (low versus high, empty versus full) and In March 2011, NHTSA issued its road surface friction levels (e.g., wet, increase in vehicle lateral acceleration, which may increase even more if the latest Vehicle Safety and Fuel Economy dry, icy, snowy). Rulemaking and Research Priority Plan • Sudden steering maneuvers to driver accelerates the vehicle in preparation to merge. (Priority Plan).10 The Priority Plan avoid a crash—The driver makes an describes the agency plans for abrupt steering maneuver, such as a C. NTSB Safety Recommendations rulemaking and research for calendar single- or double-lane-change maneuver, The National Transportation Safety years 2011 to 2013. The Priority Plan or attempts to perform an off-road Board (NTSB) has issued several safety includes stability control on truck recovery maneuver, generating a lateral recommendations relevant to ESC tractors and large buses, and states that acceleration that is sufficiently high to systems on heavy and other vehicles. the agency plans to develop test cause roll or yaw instability. One is H–08–15, which addresses ESC procedures for a Federal motor vehicle Maneuvering a vehicle on off-road, systems and collision warning systems safety standard on stability control for unpaved surfaces such as grass or gravel with active braking on commercial truck tractors, with the countermeasures may require a larger steering input vehicles. Recommendations H–11–07 of roll stability control and electronic (larger wheel slip angle) to achieve a and H–11–08 specifically address stability control, which are aimed at given vehicle response, and this can stability control systems on commercial addressing rollover and loss-of-control lead to a large increase in lateral motor vehicles and buses with a GVWR crashes. acceleration once the vehicle returns to above 10,000 pounds. Two other safety the paved surface. This increase in E. International Regulation recommendations, H–01–06 and H–01– lateral acceleration can cause the 07, relate to adaptive cruise control and The United Nations (UN) Economic vehicle to exceed its roll or yaw stability collision warning systems on Commission for Europe (ECE) threshold. commercial vehicles, and are indirectly Regulation 13, Uniform Provisions • Loading conditions—The vehicle related to ESC on heavy vehicles Concerning the Approval of Vehicles of yaw due to severe over-steering is more because all these technologies require Categories M, N and O with Regard to likely to occur when a vehicle is in a the ability to apply brakes without Braking, has been amended to include lightly loaded condition and has a lower driver input. Annex 21, Special Requirements for center of gravity height than it would • H–08–15: Determine whether Vehicles Equipped with a Vehicle have when fully loaded. Heavy vehicle equipping commercial vehicles with Stability Function. Annex 21’s rollovers are much more likely to occur collision warning systems with active requirements apply to trucks with a when the vehicle is in a fully loaded braking 7 and electronic stability control GVWR greater than 3,500 kg (7,716 lb), condition, which results in a high center systems will reduce commercial vehicle buses with a seating capacity of 10 or of gravity for the vehicle. Cargo placed accidents. If these technologies are more (including the driver), and trailers off-center in the trailer may result in the determined to be effective in reducing with a GVWR greater than 3,500 kg vehicle being less stable in one direction accidents, require their use on (7,716 lb). Trucks and buses are than in the other. It is also possible that commercial vehicles. required to be equipped with a stability improperly secured cargo can shift • H–11–07: Develop stability control system that includes rollover control while the vehicle is negotiating a curve, system performance standards for all and directional control, while trailers thereby reducing roll or yaw stability. commercial motor vehicles and buses are required to have a stability system Sloshing can occur in tankers with a gross vehicle weight rating that includes only rollover control. The transporting liquid bulk cargoes, which greater than 10,000 pounds, regardless directional control function must be is of particular concern when the tank of whether the vehicles are equipped demonstrated in one of eight tests, and is partially full because the vehicle may with a hydraulic or pneumatic brake the rollover control function must be experience significantly reduced roll system. demonstrated in one of two tests. For stability during certain maneuvers. • Road surface conditions—The road 7 Active braking involves using the vehicle’s 8 See supra, note 6. surface condition can also play a role in brakes to maintain a certain, preset distance 9 Id. at 28–29. the loss of control a vehicle experiences. between vehicles. 10 See Docket No. NHTSA–2009–0108–0032.

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compliance purposes, the ECE wheels are turned. As the steering wheel tires) or severe oversteer (loss of traction regulation requires a road test to be is turned, the displacement of the front at the rear tires). In a combination performed with the function enabled wheels generates a slip angle at the front vehicle, a loss of traction at the trailer and disabled, or as an alternative wheels and a lateral force is generated. wheels would result in the trailer accepts results from a computer That lateral force leads to vehicle swinging out of its intended path. simulation. No test procedure or pass/ rotation, and the vehicle starts rotating However, if the lateral forces generated fail criterion is included in the about its center of gravity. at the tires result in a vehicle lateral regulation, but it is left to the discretion This rotation leads to Phase 2. In acceleration that exceeds the rollover of the Type Approval Testing Authority Phase 2, the vehicle’s yaw causes the threshold of the vehicle, then rollover in agreement with the vehicle rear wheels to experience a slip angle. will result. manufacturer to show that the system is That causes a lateral force to be generated at the rear tires, which leads Lateral acceleration is the primary functional. The implementation date of cause of rollovers. Figure 1 depicts a Annex 21 is 2012 for most vehicles, to vehicle rotation. All of these actions establish a steady-state turn in which simplified rollover condition. As with a phase-in based on the vehicle shown, when the lateral force (i.e., type. lateral acceleration and yaw rate are constant. lateral acceleration) is sufficient large III. Stability Control Technologies In combination vehicles, which and exceeds the roll stability threshold of the tractor-trailer combination A. Dynamics of a Rollover typically consist of a tractor towing a semi-trailer, an additional phase is the vehicle, the vehicle will roll over. Many Whenever a vehicle is steered, the turning response of the trailer. Once the factors related to the drivers’ lateral forces that result from the tractor begins to achieve a yaw and maneuvers, heavy vehicle loading steering input lead to one of the lateral acceleration response, the trailer conditions, vehicle handling following results: (1) Vehicle maintains begins to yaw as well. This leads to the characteristics, roadway design, and directional control; (2) vehicle loses trailer’s tires developing slip angles and road surface properties would result in directional control due to severe producing lateral forces at the trailer various lateral accelerations and understeer or plowing out; (3) vehicle tires. Thus, there is a slight delay in the influences on the rollover propensity of loses directional control due to severe turning response of the trailer when a vehicle. For example, given other oversteer or spinning out; or (4) vehicle compared to the turning response of the factors are equal, a vehicle entering a experiences roll instability and rolls tractor. curve at a higher speed is more likely to over. If the lateral forces generated at either roll than a vehicle entering the curve at A turning maneuver initiated by the the front or the rear wheels exceed the a lower speed. Also, transporting a high driver’s steering input results in a friction limits between the road surface center of gravity (CG) load would vehicle response that can be broken and the tires, the result will be a vehicle increase the rollover probability more down into two phases. Phase 1 is the loss-of-control in the form of severe than transporting a relatively lower CG yaw response that occurs when the front understeer (loss of traction at the steer load.

Stability control technologies help a or RSC, which is designed to help control, or ESC,11 which is designed to driver maintain directional control and prevent on-road, untripped rollovers by help to reduce roll instability. Two automatically decelerating the vehicle 11 In light vehicles, the term ESC generally types of heavy vehicle stability control using brakes and engine control. The describes a system that helps the driver maintain technologies have been developed. One other technology is electronic stability directional control and typically does not include such technology is roll stability control the RSC function because these vehicles are much less prone to untripped rollover.

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assist the driver in mitigating severe In comparison, a trailer-based RSC D. How ESC Prevents Loss of Control oversteer or understeer conditions by system has an ECU mounted on the automatically applying selective brakes trailer, which typically monitors the Like an RSC system, an ESC system to help the driver maintain directional trailer’s wheel speeds, the trailer’s has a lateral acceleration sensor. control of the vehicle. On heavy suspension to estimate the trailer’s However, it also has two additional vehicles, ESC also includes the RSC loading condition, and the trailer’s sensors to monitor a vehicle for loss of function described above. lateral acceleration. When a high lateral directional control, which may result acceleration that is likely to cause the due to either understeer or oversteer. B. Description of RSC System Functions trailer to rollover is detected, the ECU The first additional sensor is a steering Currently, RSC systems are available commands application of the trailer wheel angle sensor, which senses the for air-braked tractors with a GVWR of brakes to slow the combination vehicle. intended direction of a vehicle. The greater than 11,793 kilograms (26,000 In this case, the trailer brakes on the other is a yaw rate sensor, which pounds) and for trailers. A tractor-based outside wheels can be applied with full measures the actual turning movement RSC system consists of an electronic pressure since the ECU can directly of the vehicle. When a discrepancy control unit (ECU) that is mounted on monitor the trailer wheels for braking- between the intended and actual a vehicle and continually monitors the related lockup. The system modulates headings of the vehicle occurs, it is vehicle’s speed and lateral acceleration the brake pressure as needed to achieve because the vehicle is in either an based on an accelerometer, and maximum braking force without locking understeering (plowing out) or an estimates vehicle mass based on engine the wheels. However, a trailer-based oversteering (spinning out) condition. torque information.12 The ECU RSC system can only apply the trailer The ESC system responds to such a continuously estimates the roll stability brakes to slow a combination vehicle, discrepancy by automatically threshold of the vehicle, which is the whereas a tractor-based RSC system can intervening and applying brake torque lateral acceleration above which a apply brakes on both the tractor and selectively at individual wheel ends on trailer. combination vehicle will roll over. the tractor, by reducing engine torque When the vehicle’s lateral acceleration C. Description of ESC System Functions output to the drive axle wheels, or by both means. If only the wheel ends at approaches the roll stability threshold, Currently, ESC systems are available the RSC system intervenes. Depending one corner of the vehicle are braked, the for heavy vehicles, including truck uneven brake force will create a on how quickly the vehicle is tractors and buses, equipped with air approaching the estimated rollover correcting yaw moment that causes the brakes. An ESC system incorporates all vehicle’s heading to change. An ESC threshold, the RSC system intervenes by of the inputs of an RSC system. In system also has the capability to reduce one or more of the following actions: addition, an ESC system monitors the engine torque output to the drive Decreasing engine power, using engine steering wheel angle and yaw rate of the wheels, which effectively reduces the braking, applying the tractor’s drive-axle vehicle.13 These system inputs are vehicle speed and helps the wheels to brakes, or applying the trailer’s brakes. monitored by the system’s ECU, which When RSC systems apply the trailer’s estimates when the vehicle’s directional regain traction. This means of brakes, they use a pulse modulation response begins to deviate from the intervention by the ESC system may protocol to prevent wheel lockup driver’s steering command, either by occur separate from or simultaneous because tractor stability control systems oversteer or understeer. An ESC system with the automatic brake application at cannot currently detect whether or not intervenes to restore directional control selective wheel ends. An ESC system is the trailer is equipped with ABS. Some by taking one or more of the following further differentiated from an RSC RSC systems also use a steering wheel actions: Decreasing engine power, using system in that it has the ability to angle sensor, which allows the system engine braking, selectively applying the selectively apply the front steer axle to identify potential roll instability brakes on the truck tractor to create a brakes while the RSC system does not events earlier. counter-yaw moment to turn the vehicle incorporate this feature. An RSC system can reduce rollovers, back to its steered direction, or applying Figure 2 illustrates the oversteering but is not designed to help to maintain the brakes on the trailer. An ESC system and understeering conditions. While directional control of a truck tractor. enhances the RSC functions because it Figure 2 may suggest that a particular Nevertheless, RSC systems may provide has the added information from the vehicle loses control due to either some additional ability to maintain steering wheel angle and yaw rate oversteer or understeer, it is quite directional control in some scenarios, sensors, as well as more braking power possible that a vehicle could require such as in a low-center-of-gravity because of its additional capability to both understeering and oversteering scenario, where an increase in a lateral apply the tractor’s steer axle brakes.14 interventions during progressive phases acceleration may lead to yaw instability of a complex crash avoidance maneuver rather than roll instability. 13 Because ESC systems must monitor steering such as a double lane change. inputs from the tractor, ESC systems are not available for trailers. 12 RSC systems are not presently available for 14 This is a design strategy to avoid the the steering axle without knowing where the driver large buses. unintended consequences of applying the brakes on is steering the vehicle.

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Oversteering. The right side of Figure vehicle’s heading is changing less • Maneuvers during tire tread 2 shows that the truck tractor whose quickly than appropriate for the driver’s separation or sudden tire deflation driver has lost directional control intended path (i.e., the yaw rate is too events. low). In other words, the vehicle is not during an attempt to drive around a F. Difference in Vehicle Dynamics turning right sufficiently to remain on right curve. The rear wheels of the Between Light Vehicles and Heavy the right curve and is instead heading tractor have exceeded the limits of road Vehicles traction. As a result, the rear of the off to the left. The ESC system tractor is beginning to slide. This would momentarily applies the right rear On April 6, 2007, the agency lead a vehicle without an ESC system to brake, creating a rightward rotational published a final rule that established spin out. If the tractor is towing a trailer, force, to turn the heading of the vehicle FMVSS No. 126, Electronic Stability as the tractor in the figure is, this would back to the correct path. Again, it will Control Systems, which requires all result in a jackknife crash. In such a also cut engine power to gently slow the passenger cars, multipurpose passenger crash, the tractor spins and may make vehicle and, if necessary, apply vehicles, trucks and buses with a GVWR physical contact with the side of the additional brakes (while maintaining of 4,536 kg (10,000 lb) or less to be trailer. The oversteering tractor in this the uneven brake force to create the equipped with an electronic stability figure is considered to be yaw-unstable necessary yaw moment). control system beginning in model year 15 because the tractor rotation occurs 2012. The rule also requires a phase- E. Situations in Which Stability Control in of 55 percent, 75 percent, and 95 without a corresponding increase in Systems May Not Be Effective steering wheel angle by the driver. In a percent of vehicles produced by each vehicle equipped with ESC, the system A stability control system will not manufacturer during model years 2009, immediately detects that the vehicle’s prevent all rollover and loss-of-control 2010, and 2011, respectively, to be heading is changing more quickly than crashes. A stability control system has equipped with a compliant ESC system. appropriate for the driver’s intended the capability to prevent many The system must be capable of applying path (i.e., the yaw rate is too high). To untripped on-road rollovers and first- brake torques individually at all four counter the leftward rotation of the event loss-of-control events. wheels, and must comply with the vehicle, it momentarily applies the right Nevertheless, there are real-world performance criteria established for front brake, thus creating a rightward situations in which stability control stability and responsiveness when (clockwise) counter-rotational force and systems may not be as effective in subjected to the sine with dwell steering turning the heading of the vehicle back avoiding a potential crash. Such maneuver test. For light vehicles, the focus of the to the correct path. It will also cut situations include: • FMVSS No. 126 is on addressing yaw engine power to gently slow the vehicle Off-road recovery maneuvers in which a vehicle departs the roadway instability, which can assist the driver and, if necessary, apply additional in preventing the vehicle from leaving brakes (while maintaining the uneven and encounters an incline too steep to effectively maneuver the vehicle or an the roadway, thereby preventing brake force to create the necessary yaw fatalities and injuries associated with moment). The action happens quickly unpaved surface that significantly reduces the predictability of the crashes involving tripped rollover, so that the driver does not perceive the which often occur when light vehicles need for steering corrections. vehicle’s handling • Entry speeds that are much too high run off the road. The standard does not Understeering. The left side of Figure for a curved roadway or entrance/exit include any equipment or performance 2 shows a truck tractor whose driver has ramp requirements for roll stability. lost directional control during an • Cargo load shifts on the trailer The dynamics of light vehicles and attempt to drive around a right curve, during a steering maneuver heavy vehicles differ in many respects. except that in this case, it is the front • Vehicle tripped by a curb or other First, on light vehicles, the yaw stability wheels that have exceeded the limits of roadside object or barrier threshold is typically lower than the roll road traction. As a result, the tractor is • Truck rollovers that are the result of stability threshold. This means that a sliding at the front (‘‘plowing out’’). collisions with other motor vehicles light vehicle making a crash avoidance Such a vehicle is considered to be yaw- • Inoperative antilock braking maneuver, such as a lane change on a stable because no increase in tractor systems—the performance of stability dry road, is more likely to reach its yaw rotation occurs when the driver control systems depends on the proper stability threshold and lose directional increases the steering wheel angle. functioning of ABS control before it reaches its roll stability However, the driver has lost directional • Brakes that are out-of-adjustment or threshold and rolls over. On a heavy control of the tractor. In this situation, other defects or malfunctions in the the ESC system rapidly detects that the ESC, RSC, or brake system. 15 72 FR 17236.

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vehicle, however, the roll stability The longer wheelbase of a heavy control engine torque. The agency also threshold is lower than the yaw stability vehicle, compared with a light vehicle, developed a ramp steer maneuver to threshold in most operating conditions, results in a slower response time, which evaluate the roll stability performance of primarily because of its higher center of gives the stability control system the a stability control system, and gravity height.16 As a result, there is a opportunity to intervene and prevent investigated a sine with dwell maneuver greater propensity for a heavy vehicle, rollovers. to evaluate both yaw and roll stability particularly in a loaded condition, to Finally, the larger number of wheels performance. In addition to tests roll during a severe crash avoidance on a heavy vehicle, as compared to a conducted on combination unit trucks, maneuver or when negotiating a curve, light vehicle, results in making heavy the VRTC research program included than to become yaw unstable, as vehicles less likely to yaw on dry road testing of three large buses equipped compared with light vehicles. surface conditions. with ESC using these test maneuvers. As Second, a tractor-trailer combination As a result of the differences in part of the research at VRTC, the agency unit is comprised of a power unit and vehicle dynamics between light vehicles also developed data collection and one or more trailing units with one or and heavy vehicles, the requirements in analysis methods to characterize the more articulation points. In contrast, FMVSS No. 126 for light vehicle ESC performance of stability control systems. although a light vehicle may systems cannot translate directly into NHTSA researchers began updating occasionally tow a trailer, a light vehicle requirements for heavy vehicles. their vehicle dynamics simulation is usually a single rigid unit. The tractor Nevertheless, many requirements in programs to include a stability control and the trailer have different center of FMVSS No. 126 are pertinent to heavy model, and coordinated with gravity heights and different lateral vehicles because they do not relate to researchers at the National Advanced acceleration threshold limits for any difference in vehicle dynamics Driving Simulator (NADS) at the rollover. A combination vehicle rollover between light vehicles and heavy University of Iowa to add stability frequently begins with the trailer where vehicles. For example, the ESC system control modeling capability to their the rollover is initiated by trailer wheel malfunction detection and telltale tractor trailer simulations. NHTSA lift. The trailer roll torque is transmitted requirements already developed for sponsored a research program with the to the tractor through the vehicles’ light vehicles can be translated to heavy NADS to evaluate potential RSC and articulation point, which subsequently vehicles. ESC effectiveness in several tractor- leads to tractor rollover. In addition to IV. Research and Testing trailer driving scenarios involving potential rollover and loss of control, the trailer’s loading condition, the NHTSA has been studying ways to trailer rollover threshold is also related using sixty professional truck drivers prevent untripped heavy vehicle who were recruited as test participants. to the torsional stiffness of the trailer rollovers for many years. In the mid- body. A trailer with a low torsional NHTSA purchased three tractors 1990s, the agency sponsored the equipped with ESC or RSC systems for stiffness, such as a flatbed open trailer, development of a prototype roll stability would typically experience wheel lift testing: A Freightliner 6x4 17 tractor that advisor (RSA) system that displayed had ESC as a production option, a earlier during a severe turning information to the driver regarding the maneuver than a trailer with a high Sterling 4x2 tractor that had RSC as a truck’s roll stability threshold and the production option, and a Volvo 6x4 torsional stiffness, such as a van trailer. peak lateral acceleration achieved Hence, compared with a light vehicle, tractor that had ESC included as during cornering maneuvers. This was standard equipment. NHTSA also the roll dynamics of a tractor trailer followed by a fleet operational test combination vehicle is a more complex obtained a RSC control unit that could sponsored by the Federal Highway be retrofitted on the Freightliner 6x4 interaction of forces acting on the units Administration, under the Department tractor so that it could be comparatively in the combination, as influenced by the of Transportation’s Intelligent Vehicle tested with both ESC and RSC. The maneuver, the loading condition, and Initiative. The tractors were equipped agency also purchased a Heil 9,200- the roadway. with a RSA system using an engine gallon tanker semitrailer that was Unlike with light vehicles, there is a retarder, which was an early equipped with a trailer-based RSC large range of loading scenarios possible configuration of an RSC system. As that system, and retrofitted a Fruehauf 53- for a given heavy vehicle, particularly test program was concluding, industry foot van semitrailer with a trailer-based for truck tractors towing trailers. A developers of stability control systems RSC system. NHTSA also obtained three tractor-trailer combination vehicle can began to add tractor and trailer large buses equipped with stability be operated empty, loaded to its foundation braking capabilities to control systems: A 2007 MCI D4500 maximum weight rating, or loaded increase the effectiveness these systems. (MCI #1), a 2009 Prevost H3, and a anywhere in between the two extremes. In 2006, the agency initiated a test second 2007 MCI D4500 (MCI #2). The The weight of a fully loaded program at the Vehicle Research and MCI buses were equipped with a combination vehicle is generally more Test Center (VRTC) to conduct track Meritor WABCO ESC system and the than double that of the vehicle with an testing on RSC- and ESC-equipped Prevost was equipped with a Bendix empty trailer. Furthermore, the load’s tractors and semitrailers. The initial ESC system. center of gravity height can vary over a testing focused only on roll stability Although the manufacturers of truck large range, which can have substantial testing and provided comparative data tractors and large buses and the effects on the dynamics of a on the performance of the different suppliers of stability control systems combination vehicle. stability control systems in several test have performed extensive development Third, due to greater length, mass, maneuvers. Subsequent testing focused and mass moments of inertia of heavy on refining test maneuvers and vehicles, they respond more slowly to 17 The 6x4 description for a tractor represents the developing performance metrics total number of wheel positions (six) and the total steering inputs than do light vehicles. suitable for a safety standard. The number of wheel positions that are driven (four), agency studied a slowly increasing steer which means that the vehicle has three axles with 16 One instance where a heavy vehicle’s yaw two of them being drive axles. Similarly, a 4x2 stability threshold might be higher than its roll maneuver that would characterize a tractor has four wheel positions, two of which are stability threshold is in an unloaded condition on tractor’s steering system and verify the driven, meaning that the vehicle has two axles, one a low-friction road surface. ability of a tractor-based system to of which is a drive axle.

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work to bring these systems to the study the effectiveness of RSC and ESC loss-of-control and rollover crashes market, there are few sources of in a range of realistic scenarios through within the national databases proved a objective evaluations for testing on hardware-in-the-loop simulation testing, difficult task because the databases are stability control systems in the public and through case reviews by a panel of developed for general use and this domain beyond the research programs experts; (3) to apply the results of this project required very precise definitions described above. The agency research to generate national estimates of loss-of-control and rollover (e.g., coordinated with truck, bus, and from the Trucks Involved in Fatal tripped versus untripped). Relying on stability control system manufacturers Accidents (TIFA) and General Estimates the general loss-of-control or rollover throughout the VRTC test program so System (GES) crash databases of the categories captures a wide range of that industry organizations had the safety benefits of RSC and ESC in crashes, many of which cannot be opportunity to contribute additional test preventing tractor-trailer crashes; and prevented by the stability control data and other relevant information on (4) to review crash data from 2001 technology. Furthermore, many of the test maneuvers that the agency could through 2007 from a large trucking fleet crashes involved vehicles that were not consider for use during the research that had started purchasing RSC on all equipped with ABS. Because ABS is program. Potential maneuvers suggested of its new tractors starting in 2004, to now mandatory for the target population by industry included a decreasing determine if there was an influence of of vehicles, the researchers had to factor radius test from the Truck & Engine this system on reducing crashes. in what effect the presence of ABS on Manufacturers Association (EMA),18 a The LTCCS was a joint study the vehicle may have reduced the sinusoidal steering maneuver and a undertaken by the Federal Motor Carrier likelihood of or prevented the crash. ramp with dwell maneuver from Safety Administration (FMCSA) and Second, the LTCCS was highly Bendix, and a lane change maneuver (on NHTSA, based on a sample of 963 valuable in providing a greater level of a large diameter circle) from Volvo.19 In crashes between April 2001 and detail concerning rollover and loss-of- late 2009, the EMA provided results December 2003 with a reported injury or control crashes, which was used to from their tests of the ramp steer, sine fatality involving 1,123 trucks with a construct a number of relevant crash with dwell, and ramp with dwell GVWR over 10,000 pounds. The LTCCS scenarios so that the technical potential maneuvers to NHTSA. The agency crash data formed the backbone for this of the candidate RSC and ESC evaluated these data from a measures-of- study because of the high quality and technologies could be estimated performance perspective. EMA provided consistent detail contained in the case systematically. However, the inability to data in December 2010 discussing files. Included in the LTCCS are determine with confidence if a vehicle additional testing with the sine with categorical data, comprehensive lost control and the lack of detailed dwell, J-turn, and a wet-Jennite drive narrative descriptions of each crash, information on driver input and vehicle through maneuver. Additional details scene diagrams, and photographs of the state placed limitations on the ability to on these research programs are included vehicle and roadway from various assess the potential for stability control in the sections below. angles. This information allowed the technologies to alter the outcome of a researchers to achieve a high level of particular crash scenario. In contrast, for A. UMTRI Study understanding of the crash mechanics rollover crashes, it was clear that NHTSA sponsored a research program for particular cases. The LTCCS was rollover occurred. Tire marks and road with Meritor WABCO and the used to help develop the crash scenarios alignment provide strong evidence of University of Michigan Transportation for modeling (hardware-in-the-loop) the vehicle path and the point of Research Institute (UMTRI) to examine performed as part of the engineering instability. the potential safety effectiveness of analyses for this stability control Third, UMTRI concluded that ESC stability control systems for five-axle project. In addition, LTCCS cases of systems would provide more overall tractor-trailer combination vehicles. The interest with respect to stability control safety benefits than RSC systems. The systems investigated included both RSC systems were also reviewed by a panel difference between the estimated and ESC.20 The research results are of three experts (two from UMTRI and effectiveness of RSC and ESC varied provided in the report ‘‘Safety Benefits one from industry) to help estimate the among crash scenarios. ESC systems of Stability Control Systems for Tractor- safety benefits of RSC and ESC. were slightly more effective at Semitrailers.’’ A copy of this report has One method for assessing the safety preventing rollovers than RSC systems been included in the docket.21 benefits of vehicle technologies is to and much more effective at preventing The objectives of the study were: (1) analyze crash datasets containing data loss-of-control crashes. To use the Large Truck Crash Causation on the safety performance of vehicles Finally, the safety benefits estimates Study (LTCCS) to define typical pre- equipped with the subject technology. derived from this study were limited to crash scenarios and identify factors However, because the deployment of the five-axle tractor-trailer combination associated with loss-of-control and stability control technologies for large vehicles, which constitute a majority of rollover crashes for tractor-trailers; (2) to trucks is still in its early stages, national the national tractor fleet. However, the crash databases do not yet have study did not include benefits estimates 18 EMA was formerly known as the Truck sufficient cases that can be used to for multi-trailer combinations or for Manufacturers Association (TMA). Many docket evaluate the safety performance of materials refer to EMA as TMA. tractors not towing a trailer. stability control technology. Given this 19 Presentations from briefings NHTSA had with B. Simulator Study EMA have been included in the docket. See Docket limitation, this study used an indirect Nos. NHTSA–2010–0034–0025 through NHTSA– method to estimate the safety NHTSA sponsored a research study 2010–0034–0031; Docket Nos. NHTSA–2010–0034– performance of stability control with the University of Iowa to study the 0041 and NHTSA–2010–0034–0042. Research notes provided by EMA, Bendix, and Volvo Trucks have technologies based on probable outcome effectiveness of heavy truck electronic also been included in the docket. See Docket Nos. estimates derived from hardware-in-the- stability control systems in reducing NHTSA–2010–0034–0032 through NHTSA–2010– loop simulation, field test experience, jackknife and rollover incidents using 0034–0040. expert panel assessment, and crash data the NADS–1 National Advanced Driving 20 A similar study has been initiated with respect to straight trucks over 10,000 pounds GVWR. from trucking fleets. Simulator. The NADS–1 is a high- 21 DOT HS 811 205 (Oct. 2009), Docket No. UMTRI’s study made several fidelity, full motion driving simulator NHTSA–2010–0034–0006 conclusions. First, identifying relevant with a 360-degree visual display system

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that is typically used for the study of consisted of lane incursion from the left The testing was conducted in three driver behavior. Sixty professional truck side on a snow-covered road and from phases. Phase I research focused on drivers were recruited to participate in the right side on a dry road surface, with understanding how stability control the study. The participants drove a each event necessitating a sudden lane systems performed. Phase II research typical tractor-semitrailer in five change to avoid collision. These events focused on the development of a scenarios designed to have a high provided a greater challenge for the dynamic test maneuver to evaluate the potential for rollover or jackknife. The stability control systems due to the roll stability of tractor semitrailers and study used the NADS heavy truck cab aggressive steering and braking inputs large buses. Phase III research focused and vehicle dynamics model to simulate by the drivers. Neither stability control on the development of a dynamic test a typical 6x4 tractor-trailer combination system showed benefits in preventing maneuver to evaluate the yaw stability vehicle in a baseline (ABS-only), RSC- rollover on the dry road surface. ESC of truck tractors and large buses. equipped, and ESC-equipped systems did provide improved vehicle The Phase I and II research results are configurations, using twenty truck control on the snow-covered surface; documented in the report ‘‘Tractor drivers per configuration. The purpose however, two jackknife events still Semi-Trailer Stability Objective of the study was to determine the occurred with the ESC system. A large Performance Test Research—Roll effectiveness of both roll stability number of jackknife events occurred on Stability.’’ 23 The Phase III research control and yaw stability control the snow-covered surface with the RSC results for truck tractors are documented systems, to demonstrate driver behavior system (11 loss-of-control events in 20 in the report ‘‘Tractor Semitrailer while using stability control systems, runs) which may have been a result of Stability Objective Performance Test and to help NHTSA refine safety the aggressive RSC braking strategy Research—Yaw Stability.’’ 24 The benefits estimates for heavy truck found in the model interfering with the information provided in sections IV.C.1, stability technologies.22 driver’s ability to maintain steering IV.C.2, and IV.C.3 below is based on The NADS truck model performance control of the tractor. these two reports. The motorcoach was compared with test track data from The NADS research study indicated research is documented in the report ‘‘Test Track Lateral Stability VRTC. The test maneuver used was a that the RSC system showed a Performance of Motorcoaches Equipped ramp steer maneuver with a steering statistically significant benefit in with Electronic Stability Control wheel angle of 190 degrees and an preventing rollovers on both curves and Systems.’’ 25 The information in section angular steering rate of 175 degrees per exit ramps on dry, high-friction road IV.C.4 is based on this report. second. The steering angle was held surfaces. The tractors equipped with constant for five seconds after reaching RSC and ESC systems showed a benefit 1. Effects of Stability Control Systems— 190 degrees, and then returned to zero. over the baseline tractor in assisting Phase I Steering inputs on the NADS were drivers to avoid a jackknife on a low- The test vehicles used in Phase I performed manually rather than by friction road surface and a rollover on included a 2006 Freightliner 6x4 tractor using an automated steering machine. a high-friction road surface when equipped with air disc brakes and a The RSM was performed in the NADS encountering a directional change due Meritor WABCO ESC system as factory- to both the right and left directions to roadway geometry. However, in several installed options, a 2006 Volvo 6x4 check for any simulation abnormalities, instances the ESC system was found to tractor with S-cam drum brakes and a and was performed for the baseline, activate at abnormally high levels of Bendix ESC system included as RSC, and ESC test conditions. Exact lateral acceleration in a curve with a standard equipment, and a 2000 matching of values to the test track data high-friction road surface. Although the Fruehauf 53-foot van trailer that was was not possible because the NADS reason for this was not determined, retrofitted with a Meritor WABCO model was developed by simulating the there may have been problems with the trailer-based RSC system. Tests were braking properties of a Freightliner mass estimation algorithm or vehicle conducted by enabling and disabling the tractor while using the inertial parameter inaccuracies in the model. stability control systems on the tractor properties of a Volvo tractor. Also, the and the trailer to compare the NADS was modeled with rigid body C. NHTSA Track Testing individual performance of each system, tractor and trailer vehicle models that NHTSA researchers at VRTC in East evaluate the performance of the did not include the torsional chassis Liberty, Ohio, initiated a test program in combined tractor and trailer stability compliance that is a variable in actual 2006 to evaluate the performance of control systems, establish the baseline vehicles. The result of the testing was stability control systems under performance of each tractor-trailer that the NADS model tractor-semitrailer controlled conditions on a test track, combination without any stability experienced wheel lift at slightly lower and to develop objective test procedures control system. All tests were conducted speeds in the RSM in all three and measures of performance that could with the tractor connected to the trailer, conditions (baseline, RSC, and ESC) form the basis of a new FMVSS. in either the unloaded condition (lightly than in the VRTC track tests. An Researchers tested three truck tractors, loaded vehicle weight (LLVW)) or additional comparison of VRTC track all of which were equipped with an RSC loaded to a 80,000 pound combination test data and the NADS ESC model was or ESC system (one vehicle was tested weight with the ballast located to performed for lane change maneuvers at with both an RSC and ESC system), one produce either a low or high center of 45 and 50 mph and showed that the trailer equipped with a trailer-based gravity height (low CG or high CG) NADS ESC system responses closely RSC system, and three large buses loading condition. During testing, all matched the responses of the actual test equipped with an ESC system. vehicle. Additionally, the agency tested five 23 DOT HS 811 467 (May 2011), Docket No. The maneuvering events used to baseline semi-trailers not equipped with NHTSA–2010–0034–0009. Results from Phase I are assess the influence of ESC systems a stability control system, including an also summarized in the paper ‘‘NHTSA’s Class 8 unbraked control trailer that is used to Truck-Tractor Stability Control Test Track 22 The final report is available in the docket. Effectiveness’’ (ESV 2009. Paper No. 09–0552). ‘‘Heavy Truck ESC Effectiveness Study Using conduct tractor braking tests as Docket No. NHTSA–2010–0034–0008. NADS’’ (DOT HS 811 233, November 2009), Docket prescribed by FMVSS No. 121, Air brake 24 Docket No. NHTSA–2010–0034–0046. No. NHTSA–2010–0034–0007. systems. 25 Docket No. NHTSA–2010–0034–0045.

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combination vehicles were equipped maneuver entrance speed was 20 mph The third maneuver evaluated in with outriggers. and it was incrementally increased in Phase I was a double-lane-change The first test maneuver evaluated in subsequent runs, until a test termination maneuver, in which the test driver Phase I was a constant radius circle test condition was reached. The test accelerated the vehicle up to a constant (either a 150 foot or a 200 foot radius) terminated upon the occurrence of one speed on a dry road surface and then conducted on dry pavement. In this of the following: The trailer outriggers negotiated a lane change maneuver constant radius circle test, the driver making contact with the ground, followed by a return to the original lane maintained the vehicle on the curved indicating that wheel lift was occurring; within physical boundaries (gates) path while slowly increasing the vehicle the tractor experiencing a severe marked by cones. The maneuver entry speed until the stability control system understeer condition; a stability control speed was incrementally increased in activated, wheel lift occurred, or the system brake activating; or the subsequent test runs. Although the top tractor experienced a severe understeer maneuver entry speed reaching 50 mph. speed in this maneuver was intended to condition. For both tractors in the baseline be limited to 50 mph for safety reasons, With the stability control systems configuration (stability control the test driver performed runs at speeds disabled, no cases of wheel lift were disabled), trailer wheel lift occurred in as high as 51 mph. observed under the LLVW or low CG all load combinations except for the In the baseline configuration, both condition. Under these load conditions, Freightliner in the LLVW condition, tractors completed the maneuver at 50 both tractors went into a severe which went into a severe understeer mph without wheel lift or yaw understeer condition. The LLVW tractor condition at a maneuver entry speed of instability in the LLVW and the low CG did not reach a velocity greater than 40 50 mph. For the Volvo in the LLVW loading conditions. In the high CG mph and the low CG tractor did not load condition, trailer wheel lift was loading condition, the Freightliner reach a velocity greater than 34 mph. observed when the tractor’s maximum experienced trailer wheel lift at a However, in the high CG condition with lateral acceleration exceeded 0.75g at 48 maneuver entry speed of 41 mph and the tractor ESC systems disabled, wheel mph. With stability control disabled in the Volvo experienced trailer wheel lift lift occurred in every test that resulted the low CG load condition, trailer wheel at a maneuver entry speed of 45 mph. in a lateral acceleration greater than With the ESC system, the lift was observed when the tractor’s 0.45g at 30 mph. Freightliner’s stability control system maximum lateral acceleration was With the tractor ESC systems enabled, was observed to limit peak lateral greater than 0.67g at 40 mph for the the performance of the two ESC- acceleration to approximately 0.50g, Freightliner and 0.60g at 38 mph for the equipped vehicles improved during the which prevented trailer wheel lift in the Volvo. For the high CG load condition, constant radius tests. Both ESC systems high CG load condition for tests trailer wheel lift was observed when the limited the maximum lateral performed up to 50 mph. Tests tractor’s maximum lateral acceleration acceleration of the tractor by reducing performed at 51 mph resulted in trailer was approximately 0.45g at 33 mph for the engine output torque and prevented wheel lift. The Volvo’s stability control wheel lift and severe tractor understeer the Freightliner and 0.42g at 31 mph for system limited the tractor’s maximum with the different loads tested. With the Volvo. lateral acceleration to approximately ESC systems enabled, both tractors Tractor ESC systems limited the 0.40g and prevented trailer wheel lift for tested allowed higher maximum lateral maximum lateral acceleration for both the high CG condition up to a maximum accelerations for the LLVW condition the tractor and the trailer. Wheel lift was test speed of 51 mph. compared to the low CG and high CG not observed for the range of speeds With only a trailer-based RSC system, conditions. There was little difference evaluated. For both tractors tested in the trailer wheel lift was observed during in peak lateral acceleration for the low low CG and high CG loading conditions, the high CG load condition when the CG and high CG conditions. the tractor’s ESC intervened at a speed system was overdriven at 41mph when The trailer-based RSC system limited that was well below the speed that tested with the Freightliner, which the maximum lateral acceleration by would produce trailer wheel lift. With represented no improvement over the applying the trailer brakes, which the trailer in the LLVW load condition, baseline condition. Trailer wheel lift mitigated wheel lift and understeer with the tractor’s maximum lateral was observed at 50 mph when tested the different loads tested. The maximum acceleration was limited to with the Volvo, which represented a 5 lateral acceleration of both tractors was approximately 0.60g for the Freightliner mph improvement over the baseline limited by the trailer RSC system to and the Volvo. With the trailer tested in condition. When tested with this below 0.50g for the LLVW condition, either the low CG or high CG load maneuver in the high CG load 0.40g to 0.50g for the low CG condition, conditions, the tractor’s lateral condition, the trailer-based RSC system and 0.35g to 0.40g for the high CG acceleration was limited to 0.50g and activated the trailer brakes at entrance condition. 0.40g for the Freightliner and Volvo speeds of 30 and 33 mph for the When both tractor- and trailer-based respectively. Freightliner and Volvo, respectively. stability control systems were enabled, The trailer-based RSC system also All stability control systems tested results were similar to the results of the improved the baseline vehicle’s roll improved the roll stability of the vehicle tractor-based stability control system for stability in the J-turn maneuver. For the over the baseline condition. For each the low CG and high CG conditions. LLVW load condition, the trailer-based maneuver, the tractor-based stability Under the LLVW condition, results were RSC system activated at speeds similar control systems were able to mitigate similar to the trailer-based RSC system to those of the tractor-based systems. trailer wheel lift at the same or higher values observed. For the low CG and high CG load maneuver entrance speeds than trailer- The second maneuver evaluated in conditions, the tractor-based systems based systems. The trailer-based RSC Phase I was a J-turn, also conducted on activated at approximately a 3 mph system was typically able to mitigate dry pavement, in which the test driver lower speed than the trailer-based RSC trailer wheel lift at a higher maneuver accelerated the vehicle to a constant system. With both systems enabled, the entry speed than the baseline condition, speed in a straight lane and then tractor-based system activated and with the exception of the double-lane- negotiated 180 degrees of arc along a mitigated the roll propensity before the change maneuver with one of the 150-foot radius curve. The initial trailer RSC system activated. tractors. In the tests with both tractor-

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based ESC systems and trailer-based maneuver is included in the FMVSS No. standard deviations in steering wheel RSC systems enabled, the tractor-based 126 test procedure for ESC systems on angle were 2.5 degrees for the Sterling, ESC system was often found to be the light vehicles. The maneuver provides 7.4 degrees for the Freightliner, and 10.2 first system to intervene to reduce wheel the steering wheel angle to lateral degrees for the Volvo, although the lift or understeer. acceleration relationship for each replacement of the tires on the Volvo Based on the results of Phase I, the vehicle, accounting for the differences may have contributed to an increase in agency determined that a performance in steering gear ratios, suspension steering wheel angle during one of the test based on the J-turn was suitable to systems and wheelbases among repeat tests. The tractor speed at the evaluate tractor and trailer stability vehicles. It also normalizes test beginning of the SIS steering input control systems. The J-turn maneuver conditions to account for variations in ranged from 29.6 to 32.2 mph for all of generates a sufficient amount of lateral test conditions, such as road surface the tests. acceleration to provide a challenging friction. The steering wheel angle After the SIS testing, tests were test at reasonable test speeds. The J-turn derived from the SIS test was used to conducted using a ramp steer maneuver maneuver is also more representative of program the automated steering to assess the roll stability of tractor- the real-world conditions, such as machine for the ramp steer maneuver trailer combinations and the curved off-ramp, that could generate discussed below. effectiveness of both types of tractor- untripped rollover. Because the results To initiate the SIS maneuver, the test based stability control systems. The from Phase I showed that tractor-based driver accelerated the vehicle to a RSM was derived from and is similar to stability control systems increased the constant speed of 30 mph on a dry road the J-turn maneuver, but instead of the roll stability by a larger margin than surface. The driver then activated the driver controlling the steering wheel to trailer-based RSC systems, NHTSA steering machine to input a steadily follow a fixed path, the steering concluded that Phase II research should increasing steering wheel angle up to controller turns the steering wheel to an focus on tractor-based stability control 270 degrees at a rate of 13.5 degrees per angle determined from the results of the systems. second. The test driver manually SIS test. One advantage of the RSM over maintained constant speed using the the J-turn maneuver is that the RSM 2. Developing a Dynamic Test Maneuver accelerator pedal while the tractor’s uses a steering machine, which allows and Performance Measure To Evaluate path radius steadily decreased and the for a more consistent and repeatable Roll Stability—Phase II tractor’s lateral acceleration steadily steering input. (a) Test Maneuver Development increased. The SIS maneuvers were To conduct the RSM, the test driver conducted with the tractor in the bobtail accelerated the vehicle to a constant The researchers at VRTC conducted condition (no trailer attached). The SIS speed of one to two mph above the Phase II to develop test methods that maneuver also demonstrated that target maneuver entry speed on a dry could evaluate stability control system tractor-based stability control systems surface and then released the throttle performance objectively and measures are capable of detecting a high lateral and de-clutched the engine. Once the of performance that would ensure that acceleration condition and intervening vehicle coasted down to the desired a stability control system could prevent by reducing the engine output torque. maneuver entry speed, the automated rollover effectively. After Phase I test The SIS maneuver was used to steering controller initiated a steering results demonstrated that a test driver’s determine the steering wheel angle input, at a constant rate of 175 degrees steering input variation could affect test projected to generate 0.5g of lateral per second, up to the steering wheel outcome, an automated steering acceleration when traveling at 30 mph. angle that was derived for the tractor in machine was used for subsequent This value varied depending on the SIS test. Once the steering wheel research. The testing focused on tractor- characteristics of the tractor such as its angle was reached (the end of ramp based stability control systems that were wheelbase and steering ratio. For input), it was held constant for five determined to be most effective in tractors, that steering wheel angle and seconds, and then the controller preventing rollovers from the Phase I lateral acceleration data was found to returned the steering wheel angle back research. have a linear relationship at the lateral to zero at a steering rate of 175 degrees Both the Freightliner and Volvo 6x4 acceleration values between 0.05 and per second. The initial maneuver entry tractors equipped with an ESC system 0.3g. Over this range of data a linear speed was 20 mph and it was from Phase I were tested, and an RSC regression method followed by linear incrementally increased in subsequent electronic control unit was also extrapolation was used to estimate the runs until a test termination condition obtained for the Freightliner. A Sterling steering wheel angle at 0.5g lateral was met. The termination conditions 4x2 equipped with a Meritor WABCO acceleration for each SIS maneuver. The were as follows: Two inches of wheel RSC system was also tested in Phase II. final steering wheel angle was then lift occurring at either the tractor drive In addition to the Fruehauf 53-foot van calculated by averaging the values from wheels or the trailer wheels; the tractor trailer used in Phase I (its trailer-based tests conducted while turning to the left reaching a severe oversteer condition RSC system was disabled throughout and while turning to the right. The (safety cables were installed to limit the the Phase II testing), five additional resulting calculated steering wheel tractor-trailer articulation angle for trailers were tested, including a second angles were 193 degrees for the testing safety); or the maneuver entry 53-foot van trailer, two 48-foot flatbed Freightliner, 199 degrees for the Volvo, speed reached 50 mph without a roll or trailers, a 9200-gallon tanker trailer, and and 162 degrees for the Sterling. This yaw instability condition. Although the a 28-foot flatbed trailer which is used as indicates that the Sterling, which was a intent of the RSM was to evaluate a control trailer in FMVSS No. 121 4x2 configuration, had a higher steering combination vehicle roll stability, brake system testing. wheel gain than the other tractors which testing with the trailers in the unloaded The first maneuver evaluated in Phase were 6x4 configurations. condition resulted in several II was a slowly increasing steer The SIS testing was repeated for the occurrences of tractor yaw instability. maneuver. The SIS maneuver has been three tractors throughout the test For all of the RSM tests, each tractor used by the agency and the industry to program to determine the consistency of was tested with all six trailers and the determine the unique dynamic the steering wheel angle calculations trailers were either unloaded, or loaded characteristics of each vehicle. This and the test speeds. The resulting to a high CG, on-highway combination

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weight appropriate for the number of having a more aggressive braking rapidly, application of the vehicle’s axles on the combination vehicle. For strategy than the ESC system tested. foundation brakes may be a more the flatbed and van trailers, the load The RSM was then performed with appropriate means of improving ballast was placed on 24-inch high each of the six trailers in the unloaded stability. tables to produce a high CG height, and condition, with the tractor stability The agency investigated four the tanker trailer was loaded with water. control system enabled with the trailer measures for development as metrics for The purpose of the RSM test is not to brakes disabled. Tests were not engine/power unit control. They were cause a rollover, but to create a high conducted with the systems disabled. truck tractor speed, truck tractor lateral lateral acceleration condition to The initial maneuver entry speed was acceleration, truck tractor longitudinal demonstrate that a stability control 20 mph and was incrementally acceleration, and actual engine torque system has the capability to reduce the increased in subsequent runs until the and driver requested engine torque. likelihood of a rollover. Typically, speed reached 50 mph, severe oversteer The forward speed of a truck tractor wheel lift occurred first at the trailer occurred, or wheel lift occurred. The appears to be directly related to the wheels although the flatbed trailer tractors with ESC systems enabled were lateral forces generated during an combinations had tractor drive wheel able to complete all but one of the RSM untripped rollover. Test data from four lift occurring first or in unison with the tests up to 50 mph without any tractor different vehicles with stability control trailer wheels. In the RSM tests with the instability or wheel lift. The Volvo enabled indicated that forward speed stability control system disabled and the tractor towing the empty tanker trailer was reduced from the target maneuver trailer in the high CG condition, wheel resulted in wheel lift of the tractor drive entrance speed of 30 mph. However, lift occurred at entry speeds between 25 wheels and the trailer wheels at a speed due to the nature of the roll maneuver, and 31 mph for all combinations of of 47 mph. it is possible for the vehicle to lose tractors and trailers. The peak tractor In comparison, most of the tests with traction on the inside wheels, which lateral acceleration at wheel lift was in the tractors equipped with RSC systems results in a reduction in vehicle speed the range of 0.45 to 0.50g, showing that towing unloaded trailers resulted in but does not necessarily enhance the high CG loading condition was severe tractor oversteer, with the tractor- vehicle stability. Lateral acceleration was a possible representative of fully loaded tractor- trailer articulation angle typically reaching the limits allowed by the safety measure of performance because of its trailers with a medium density cargo. cables. This occurred at speeds between direct relationship in producing the Tractor-based stability control 35 and 39 mph for the Freightliner 6x4 forces associated with untripped systems applied the foundation brakes tractor and between 34 and 42 mph for rollover. Data from four different on the tractor and trailer, which reduced the Sterling 4x2 tractor. However, both tractors with the stability control system the vehicle speed and lateral of these tractors were able to complete enabled indicate that each combination acceleration during the RSM. The entry the RSM up to 50 mph when coupled of tractor and stability control system speed at which wheel lift was first to the unloaded 28-foot control trailer, had a different lateral limit that the visible improved to between 31 and 42 and the Freightliner reached 50 mph system has allowed. This shows that the mph for three of the four tractors tested without wheel lift or severe understeer control strategy used by the (Freightliner RSC, Freightliner ESC, and when coupled to the unloaded tanker manufacturer is different depending on Volvo ESC). trailer. the vehicle and system used. One In tests with the trailer brakes In summary, the goal of the Phase II strategy allows the vehicle to build disabled, the entry speed at which research was to develop a test maneuver lateral acceleration to a set threshold wheel lift was detected was between 29 to challenge the roll propensity of a level and then allows that level to be and 41 mph, which showed that the truck tractor. The RSM is similar in test maintained throughout the maneuver. contribution of trailer braking to prevent severity to the J-turn and demonstrates The other strategy allows lateral wheel lift was evident, but that it was that the stability control systems are acceleration to build and then the relatively small in comparison to the able to mitigate wheel lift in most cases stability control system reduces the deceleration resulting from tractor that occurred when the stability control lateral acceleration. Both of these braking. The Sterling tractor equipped systems were disabled. In the high CG strategies were observed to increase with an RSC system had wheel lift with load condition, the ESC systems were lateral stability. Because the lateral three of the trailers at the same speed as observed to mitigate wheel lift at or acceleration limits were different for with the stability control system above the speed observed with RSC- vehicles using these control strategies, disabled, and with the other three equipped vehicles, with the exception lateral acceleration alone was not found trailers at speeds between two and four of a few instances with the to be a good measure for stability mph over the disabled test condition. In Freightliner’s ESC system. When tested control performance. all of the RSM tests, the Sterling with the unloaded test trailer, Longitudinal acceleration of a vehicle tractor’s RSC system was not as effective substantial improvements in tractor yaw is reduced when a vehicle’s stability at mitigating wheel lift for this stability were evident in the tractors control system is enabled and is directly maneuver. equipped with ESC systems during RSM related to a reduction in forward speed. The results indicated that, in general, tests. On the four vehicles tested, the stability the ESC systems provided a higher level control activation had measurable of deceleration compared to the RSC (b) Performance Measure Development differences in longitudinal acceleration, systems and typically had the higher NHTSA’s Phase II testing also but had similar disadvantages to maneuver entry speeds prior to wheel examined possible performance forward speed in being used as a lift. However, there were individual measures to evaluate roll stability. In performance metric. trailer combinations in which the RSC situations where the vehicle’s stability Engine torque measures were system performed as well or slightly limits are approached in a gradual observed to be a direct way to determine better than the ESC system on the manner, engine/power unit control can ESC activation during the SIS tests. Freightliner. We believe the better improve stability in these situations. Engine torque refers to two different performance by the RSC system in some However, in situations where stability measures. The first relates to the torque tests is attributable to the RSC system limits of the vehicle are approached output from the engine and is expressed

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as a percentage of maximum engine which ranged from 23 percent to 18 show that a ratio-based metric could be output. The second relates to the percent of maximum engine torque. more appropriate for such a throttle pedal used by the driver to The agency also investigated several performance metric. control engine torque output. This value other measures for development for Lateral acceleration ratio is calculated is also expressed as a percentage of foundation braking in rollover tests by dividing the tractor’s lateral maximum engine output and is referred because stability control systems were acceleration at a given time interval by to as the ‘‘driver requested torque.’’ observed to improve the vehicle’s roll the measured lateral acceleration at the During normal operation the ‘‘driver stability by applying the foundation end of ramp input, which is the end of requested torque’’ and ‘‘engine torque’’ brakes. The measures investigated were the steering maneuver and the point measures were observed to be equal to wheel lift, lateral acceleration, lateral near which the vehicle experiences its each other. However, during ESC acceleration ratio, trailer lateral peak lateral acceleration. The LAR was activation when engine control acceleration ratio, and trailer roll angle plotted at five equal one-second intervened, the two measures were ratio. intervals for several truck tractors and observed to be separate. In every case, Wheel lift is a direct measure of test trailers. The plots indicated sharp the ‘‘engine torque’’ was much less than performance with minimal calculations decreases in LAR caused by activation the ‘‘driver requested torque’’ and needed to determine its value. The of the stability control system. continued to reduce until vehicle measure is simple and directly A similar ratio metric for trailers, stability was regained. After careful represents the pre-crash condition that trailer lateral acceleration ratio, also review of the data the torque separation immediately precedes a rollover. If showed the ability to discriminate activity was confirmed for all the SIS wheel lift can be prevented, a rollover between vehicles with stability control test series in which stability control was cannot occur. For our research, wheel systems and those without. A third ratio enabled for each vehicle. This led the lift was considered to occur upon two metric was considered, trailer roll angle agency to conclude that this measure inches of lift for the tractor drive axle ratio based on a test trailer roll angle, was a good candidate for further wheels or the trailer wheels. Wheel lift but it did not clearly discriminate analysis and development as a measure does not always indicate that rollover is between vehicles with stability control of performance for truck tractors imminent, particularly because certain systems and those without. equipped with a stability control suspension designs will lift a wheel system. during hard cornering. We estimated the 3. Developing a Dynamic Test Maneuver The engine torque data analysis was vehicle speed that produced wheel lift and Performance Measure To Evaluate based on the test driver attempting to during the ramp steer maneuver and Yaw Stability—Phase III maintain a constant vehicle speed at the found that between 29 mph and 32 (a) Test Maneuver Development point of stability control engine torque mph, there is a high probability of intervention by making a substantial wheel lift occurring on the combination The purpose of the Phase III research increase in driver-requested engine vehicles tested. Given that only four was to develop maneuvers to evaluate torque. For the four vehicles tested, the different truck tractors and six different the yaw stability performance of driver requested engine torque after test trailers were used, we believed that stability control systems on tractors. stability control intervention was the data may not be sufficient to assess Although we have examined several between 60 percent and 100 percent of the real world service of tractors with maneuvers to evaluate yaw stability, engine output whereas the engine ESC expected to function with different two maneuvers were fully investigated torque output after stability control trailers having different torsional because other maneuvers were not able intervention ranged from zero to 60 stiffness and loads. to provide a consistent, repeatable percent. The analysis of engine torque Using lateral acceleration as a performance test. We fully considered a differentials was limited to the first four performance metric is based on the sine with dwell test maneuver that is seconds after stability control engine principle that a tractor-trailer similar to the test maneuver used in torque intervention since none of the SC combination vehicle with a high center FMVSS No. 126 for light vehicles; and systems were observed to make of gravity that achieves a certain level of a half-sine with dwell (HSWD) test substantial reapplications of engine lateral acceleration would roll over. maneuver. The steering inputs for the torque output during this initial time- Tests performed on the Freightliner in SWD and HSWD maneuvers are frame. On two vehicles engine torque combination with all trailers configured depicted in the figures below, and as interventions reduced engine output with a high-CG load, at a mean entrance discussed in additional detail, torque to zero during the first four speed of 28 mph generated a lateral variations on the steering wheel angle, seconds, and both systems allowed acceleration. The data showed that the frequency of the sine wave (cycles engine torque to be momentarily using tractor maximum lateral per second, Hz), and the dwell time reapplied to over 50 percent of engine acceleration as a performance criteria were evaluated for both maneuvers. A torque output. The Volvo had the would not discriminate between steering machine was used to achieve highest engine torque output during the vehicles equipped with stability control consistent steering wheel inputs for first four seconds after intervention, and those without it. However, it did these maneuvers.

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The test vehicles used in Phase III the Freightliner with RSC, 0.35g for the A frequency of 0.5 Hz was found to included: A 2006 Freightliner 6x4, Volvo, and 0.4g for the Sterling. require the lowest steering scalar to which was tested with both ESC and For the SWD and the HSWD test produce severe oversteer in the Sterling RSC systems; a 2006 Volvo 6x4 tractor maneuvers, the maneuver entrance and Volvo tractors in the SWD with an ESC system; and a Sterling 4x2 speed for the bobtail tractor tests was 50 maneuver, and 0.4 Hz was found to tractor equipped with an RSC system. mph, and for the tests at 60 percent require the lowest steering scalar to Although most of the testing was GAWR the entry speed was 45 mph. The produce severe oversteer in the performed using the 28-foot flatbed driver accelerated the test vehicle up to Freightliner tractor (and 0.5 Hz was the control trailer, each tractor was also a speed slightly over the desired speed second-most severe frequency for this tested with a 53-foot Strick van trailer, in a straight lane, then released the tractor). A dwell time of 1.0 second was a 48-foot Fontaine spread axle flatbed throttle and de-clutched the engine. found to result in severe tractor trailer, and a 9600-gallon Heil tanker Once the vehicle coasted down to the oversteer at lower steering scalars. Thus trailer. Tests were conducted with the desired speed, the automated steering the researchers selected a 0.5 Hz trailer brakes both enabled and disabled. machine initiated either the sinusoidal frequency and 1.0 second dwell time as or half-sine steering input, at a specified the parameters for the SWD and HSWD Two tractor loading conditions were test frequency as described below (e.g., maneuvers. However, the researchers used for both the SWD and HSWD 0.3 Hz, 0.5 Hz, etc.), with the steering also found that the SWD maneuver was testing. Each tractor was tested in the wheel angle held constant during the less sensitive to differences in steering bobtail condition (no trailer attached) dwell, as depicted in the figures. Two frequency compared to the HSWD and using a trailer loaded over the fifth dwell times were evaluated as described maneuver. wheel so that the tractor drive axle(s) below, 0.5 and 1.0 second. The initial In tests conducted with baseline was loaded to 60 percent of its gross test run began with a steering wheel tractors in the bobtail condition, no yaw axle weight rating (GAWR). The yaw angle equal to 30 percent of the angle instability occurred; however, in both instability that occurred in the RSM determined from an SIS test. The test the SWD and HSWD tests the Sterling testing showed that the unloaded 28- severity was increased in subsequent tractor experienced wheel lift at the foot control trailer was too light to runs by increasing the steering wheel tractor drive wheels. Seventy test series produce yaw instability. Therefore, angle in 10 percentage point increments were conducted on the baseline tractors additional weight was added for these until reaching 130 percent of the SIS in the 60 percent GAWR load condition, tests. Testing was conducted on two test steering wheel angle. Thus, 11 test runs with fifteen of the series terminated due surfaces: A high-friction dry road were needed to complete a test series. If to roll instability and 28 due to severe surface and a slippery wet Jennite road severe oversteer or wheel lift greater tractor oversteer. surface. than two inches was detected, then the In tests conducted with the tractor Additional SIS tests were performed, test was repeated using the previous stability control system enabled and in similar to the bobtail SIS tests described steering wheel angle in which the the 60 percent GAWR load condition, in Phase II, conducted with each tractor systems was observed to be stable. If the all of the tractors with an ESC system coupled to the 28-foot control trailer tractor-trailer was stable during the were able to complete the SWD and loaded to the 60 percent GAWR repeated run, additional tests were maneuver at test scalars up to 130 condition. The steering wheel angles performed by increasing the steering percent. However, the tractors equipped from these tests were 197 degrees for the wheel angle in 5 percent increments with RSC systems experienced severe Freightliner with ESC, 200 degrees for until instability was observed. oversteer in 12 of 15 test series at the the Freightliner with RSC, 200 degrees Tests were conducted on baseline steering scalars of 120 and 130 percent. for the Volvo, and 153 degrees for the tractors in the 60 percent GAWR In tests conducted using the HSWD Sterling. The average tractor lateral condition on dry pavement to evaluate maneuver, the ESC-equipped tractors acceleration at engine torque frequency and dwell time for the SWD completed seven of eight test series intervention in the SIS tests was 0.40g and HSWD test maneuvers. Frequencies without tractor yaw instability, and the for the Freightliner with ESC, 0.34g for between 0.3 and 0.7 Hz were evaluated. RSC-equipped tractors experienced

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severe oversteer at steering scalars acceleration, the agency examined a condition, gross person occupancy ranging from 80 to 125 percent. In both yaw rate ratio metric. The YRR weight (GPOW), included the LLVW test maneuvers, the RSC systems expresses the lateral stability criteria for weight plus the addition of 175-lb water improved tractor yaw stability the sine with dwell test to measure how dummies in each available passenger compared to the baseline tractor, but quickly the vehicle stops turning, or seat without exceeding the GVWR of the they could not maintain yaw stability at rotating about its vertical axis, after the vehicle. This condition was used to the higher steering scalars. steering wheel is returned to the represent a high CG load that a bus may Additional SWD tests were conducted straight-ahead position. Similar to the experience while in service. A third with the 53-foot van trailer and the 48- LAR, the YRR metric is the percent of loading condition was conducted with foot flatbed trailer using the 60 percent peak yaw rate that is present at a the Prevost, which added ballast to the GAWR loading condition. In eight test designated time after completion of cargo holds under the mid-section of the series conducted with the tractor steer. This performance metric is bus. This condition loaded the vehicle stability control systems enabled, seven identical to the metric used in the light to its GVWR. were completed without wheel lift or vehicle ESC system performance Test maneuvers that were conducted tractor yaw instability, but the Sterling requirement in FMVSS No. 126. Phase included the 150 ft. constant radius tractor equipped with an RSC system III research found that both LAR and increasing velocity test, SIS, RSM, tested with the 48-foot flatbed reached YRR were capable of measuring stability HSWD, and SWD. Tests were conducted a termination condition at a steering during the SWD maneuver. However, using an automated steering machine, scalar of 105 percent. In tests with while LAR was better at predicting roll except for the constant radius stability control enabled, all of the instability, YRR was better at predicting maneuvers. The severity for each test tractors coupled to the tanker trailer yaw instability. maneuver was increased either by experienced wheel lift in the SWD increasing vehicle speed or steering maneuver at scalars between 60 and 95 4. Large Bus Testing angle. percent. Researchers at VRTC tested three large SIS maneuvers were conducted under SWD tests were also conducted on a buses equipped with stability control both loading conditions, with ESC low-friction wet Jennite surface using a systems: A 2007 MCI D4500 (MCI #1), systems enabled and disabled, and in lower maneuver entry speed of 30 mph. a 2009 Prevost H3, and a second 2007 both left and right directions in order to In the baseline condition with the MCI D4500 (MCI #2). The MCI buses characterize each vehicle. Initially, the tractor stability control systems were equipped with a Meritor WABCO maneuver was executed exactly as it disabled, 43 test series were conducted ESC system and the Prevost was was for the tractor testing. However it and a termination condition was equipped with a Bendix ESC system. was observed that steering to a reached in only four test series. Testing RSC systems were not offered on large maximum steering wheel angle of 270 on the dry, high-friction surface was buses and, consequently, were not degrees generated barely over 0.3g of found to result in more yaw instabilities evaluated. All of the buses were lateral acceleration. From this, it was than the testing conducted on the low- equipped with air disc brakes. Both the clear that large buses have a larger friction, wet Jennite surface. MCI #1 and the MCI #2 had a GVWR of steering ratio, and it would take a larger In summary, the purpose of Phase III 48,000 lb and a wheelbase of 317 in., steering input to achieve the appropriate research was to develop a maneuver to and the Prevost had a GVWR of 53,000 lateral acceleration levels. The steering evaluate the yaw stability of a tractor lb and a wheelbase of 317 in. Each of wheel angle necessary to achieve 0.5g in trailer combination vehicle. VRTC the buses had three axles: A steer axle, the LLVW loading condition was 405 researchers found that the SWD a drive axle, and a non-driven tag axle. degrees for the MCI #1, 352 degrees for maneuver with a one-second dwell time The MCI #1 was equipped with the Prevost, and 407 degrees for the MCI based on a single cycle of steering input outriggers supplied by MCI and Meritor #2. In the GPOW loading condition, with a frequency of 0.5 Hz conducted on WABCO. The outriggers limited the use steering wheel angles were found to be a high friction surface appropriately of higher maneuver entry speeds for 405 degrees for the MCI #1, 383 degrees assessed the ability of an ESC system to tests without the ESC system enabled. for the Prevost, and 461 degrees for the improve yaw stability. From this At higher speeds, the lower support MCI #2. maneuver, performance measure were portion of the outrigger would dig into SIS tests were conducted at GPOW to investigated for lateral stability and the test surface and influence the evaluate the ability of the ESC system to responsiveness: the lateral acceleration dynamics of the vehicle. Therefore, tests reduce speed by limiting engine torque. ratio, which is directly correlated to roll of the MCI #1 at higher speeds had no For the three buses tested the average stability and the yaw rate ratio, which baseline performance to compare to. speed at activation for each SIS the performance metric used in FMVSS The Prevost and MCI #2 buses were maneuver ranged between 29.8 and 30.6 No. 126 for light vehicle ESC systems tested using NHTSA-designed mph. At four seconds following SC and was found to be a direct outriggers. The outriggers designed for activation the average speed for each performance measure of yaw stability. A combination vehicles were adapted for SIS had been reduced to 27.9 mph for responsiveness measure was also installation on the mid-section of each the MCI #1, 26.5 mph for the Prevost, studied to evaluate the lateral bus, just in front of its drive axle and and 26.6 mph for the MCI #2. Without displacement of a vehicle during SWD slightly behind its longitudinal center of stability control enabled, speeds did not maneuvers. gravity. Using these outriggers, the decrease. The average lateral vehicles were able to complete testing acceleration for a test series observed at (b) Performance Measure Development for all speeds, with or without ESC activation was 0.32g for MCI #1, 0.27g Phase III of NHTSA’s research also enabled. for the Prevost, 0.31g for MCI #2. examined potential measures of yaw Each bus was tested using two RSM testing was completed for each instability prevention performance. In primary simulated load conditions. The bus to evaluate their roll propensity light of the conclusion in Phase II that first condition was a lightly loaded while loaded in the LLVW and GPOW lateral acceleration ratio was a suitable vehicle weight (LLVW) that included conditions. Tests were conducted using metric to measure a stability control the weight of the test instrumentation, the same RSM protocol as the one system’s ability to prevent lateral outriggers, and driver. The second load developed for tractors. Using an

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automated steering machine scalar from 30 to 130 percent in 10 test results for the HSWD indicated that programmed with the steering wheel percent increments. A test series was the longer dwell time was more angle calculated from the SIS maneuver, terminated if the vehicle experienced challenging to stability. Unlike the tests were conducted with ESC systems wheel lift greater than 2 inches, the SWD, the lower frequencies were enabled and disabled. The initial vehicle spun out, or the steering input observed to produce wheel lift at lower maneuver entry speed was 20 mph and reached a terminating scalar of 130 steering wheel angle scalars. Tests was incrementally increased in percent. results from both the SWD and HSWD subsequent runs until two inches of No instances of spinout were maneuvers indicated that both wheel lift occurred at any of the wheels, observed during this testing, but tests at maneuvers generated dynamic the vehicle went into a severe oversteer higher steering wheel angles produced responses from the vehicles. There were condition, or the entry speed reached 50 drift. Although the buses were yaw clear differences in lateral acceleration mph without a roll or yaw instability stable in the maneuvers, the test results and yaw rate between test series condition. demonstrated that the SWD maneuver conducted with ESC systems enabled For RSM tests with ESC systems was challenging the buses’ roll compared to test series with ESC disabled and the buses loaded in the propensity. Several SWD test series with systems disabled. The data showed that LLVW condition, wheel lift was the GPOW condition produced wheel ESC systems were reducing both observed in both MCI test vehicles at lift when the ESC system was disabled. rollover and spinout propensities. speeds of 41 to 45 mph, and no wheel When the ESC systems were enabled, all However, the SWD maneuver was lift was observed for tests with the vehicles were able to complete their favored over the HSWD maneuver Prevost for the speeds tested. When series without exceeding either roll or because the SWD maneuver could be tested in the GPOW condition, wheel yaw stability thresholds. conducted in a smaller area, would be lift was observed at 35 to 39 mph for all The SWD test data from the GPOW representative of a crash avoidance or vehicles tested. load condition were analyzed to lane change maneuver, and its use in For RSM tests with ESC systems determine a frequency and dwell time FMVSS No. 126 accelerated enabled and the buses loaded in the for a candidate performance maneuver. performance measure research. LLVW condition, no instances of wheel For all tests with ESC disabled, lift were observed over the range of maneuvers with a 1.0-second dwell time This research indicates that large speeds tested. During tests in the GPOW required an equal or lower steering buses equipped with ESC systems can condition wheel lift was not observed in scalar (0 to 50 percent lower) to exceed use the same objective performance either MCI over the range of speeds a threshold of 6 degrees of yaw angle. maneuver as was developed for tractors. tested, but was observed in some of the As with the tractor testing, this Testing also indicates that the same Prevost tests at speeds between 42 and suggested that the 1.0-second dwell time performance measures can be used to 48 mph.26 was more challenging to large buses assess lateral stability and SWD testing was completed for each because it required less steering to responsiveness, but the performance bus to evaluate its yaw propensity while exceed the threshold. measures must be tailored for the loaded in the LLVW and GPOW Using only the 1.0-second dwell time vehicle differences. conditions. All tests were conducted tests, analysis to determine the optimum D. Truck & Engine Manufacturers with the ESC systems enabled and frequency for the SWD test was Association Testing disabled. Using an automated steering completed by evaluating the roll and machine, the SWD tests were run using yaw angles. Review of the test data The Truck & Engine Manufacturers steering frequencies of 0.3, 0.4, 0.5, and indicated that the largest roll and yaw Association (EMA) performed tests on 0.6 Hz, dwell times of 0.5 and 1.0 angles were produced in the maneuvers ten tractors listed in the following table seconds, and a maneuver entry speed of using 0.4 and 0.5 Hz frequencies. equipped with stability control systems 45 mph. Test severity was increased by The large buses were also tested using using the three test maneuvers increasing the steering wheel angle by a the HSWD maneuver. Like the SWD, the developed at VRTC.

TABLE 2—EMA TEST TRACTORS INCLUDING TYPE, GVWR, AND WHEELBASE

Tractor configuration GVWR Wheelbase (EMA Vehicle I.D.) Stability control type (lb) (inches)

6x4 Typical Tractor (Vehicle A) ...... ESC ...... 52,000 228 4x2 (Vehicle B) ...... ESC ...... 32,000 140 4x2 (Vehicle C) ...... RSC with steering wheel angle sensor ...... 34,700 152 6x4 Severe Service (Vehicle D) ...... ESC ...... 66,000 220 6x4 w/Pusher Axle (Vehicle E) ...... ESC ...... 86,000 270 8x6 Tridem Drive Axle (Vehicle F) ...... ESC ...... 89,000 263 6x4 w/Pusher Axle (Vehicle G) ...... ESC ...... 92,000 243 6x4 Severe Service (Vehicle H) ...... RSC ...... 60,600 246 6x4 (Vehicle I) ...... ESC ...... 52,000 232 6x4 (Vehicle J) ...... ESC ...... 52,350 245

26 Initial tests conducted with the Prevost the vehicle up to this speed and allow the driver to 44 mph with ESC enabled. Upon further demonstrated that the vehicle was able to complete to recover safely if the test needed to be aborted. investigation when preparing to de-instrument the the RSM at up to 48 mph without wheel lift for the RSM tests under the same conditions were repeated vehicle, a broken roll stabilizer bar was discovered. GPOW condition. The Prevost was not tested to 50 less than a week later. During these tests, wheel lift Researchers attributed the change in performance mph because there was not enough test area to bring greater than 2 inches was observed at speeds of 42 observed to the broken stabilizer bar.

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EMA provided its test data to the steering wheel angle for a lateral subsequent test runs was increased by agency.27 Although the tractors were not acceleration of 0.5g, and the average of 10 percent increments up to 130 percent identified by make or model, EMA the absolute value of each of the six of the steering angle. The SWD tests provided the configuration and weight runs was calculated for the final angle were conducted with two tractor ratings for each tractor. Eight tractors as in the prior SIS tests. Comparing loading conditions: Loaded to 60 were subjected to the SIS and RSM to these data to the prior SIS test results, percent of the drive axle(s) GAWR with evaluate rollover prevention, and three Vehicle B, which had the smallest angle the FMVSS No. 121 unbraked control tractors were subjected to the SWD of 126 degrees in the prior SIS tests, trailer attached (loaded tests), and in the maneuver, and the ramp with dwell showed a ten degree reduction of its unloaded condition with no trailer (RWD) maneuver on a low-friction angle in this test series. Vehicle G’s attached (bobtail tests). The maneuver surface to evaluate yaw stability. Two of angle was nearly identical (203 degrees entrance speed was 45 mph and the test the tractors were equipped with RSC in the first series vs. 205 degrees in the was conducted on dry pavement. systems and seven tractors were second series). The results of the loaded tests for equipped with ESC systems. EMA also Vehicles G and I indicated that both 2. Ramp Steer Maneuver submitted test data for several tractors remained roll and yaw stable maneuvers in which the test parameters For the RSM tests on eight tractors, through the full range of testing, and were varied. With the exception of the tractors were attached to a FMVSS there were no indications of tractor Vehicle J, EMA did not submit baseline No. 121 control trailer and were loaded wheel lift in the test comments or the test data—that is, EMA submitted data to their GVWR by placing the ballast unprocessed data. The largest steering only for maneuvers with ESC or RSC over the fifth wheel, with the ballast wheel angle produced the highest peak systems enabled. placed directly on the trailer deck lateral acceleration, which occurred resulting in a low center of gravity during the dwell portion of the 1. Slowly Increasing Steer Maneuver height. The weight on the FMVSS No. maneuver for both tractors. Vehicle I For all tractors, test data were 121 control trailer’s single axle ranged reached approximately 0.75g and provided for the SIS tests used to derive between 5,720 and 5,930 lb for all eight Vehicle G reached just under 0.6g. the steering wheel angle with each tractor tests, and the trailer brakes were Although both tractors were close in tractor in the bobtail condition. In the not enabled. While the weight on the wheelbase and tested with similar first SIS series conducted on eight of the trailer axle is nominally 4,500 lb when steering wheel angles, Vehicle G, tested tractors, three SIS tests were conducted the trailer is used for FMVSS No. 121 with its liftable axle in the lowered in each direction on a dry road surface, stopping distance tests, the increased position, was either less responsive in and a best fit linear regression was used weight in these RSM tests reflects the the SWD maneuver or its ESC to project the steering wheel angle for a added weight of the outriggers installed performed slightly better than the ESC lateral acceleration of 0.5g. The average on the trailer. In general, each of the on Vehicle I. Both tractors had similar of the absolute value of each of the six tractors was loaded to its GVWR with overall vehicle decelerations; however, runs was calculated for the final angle. the steer, drive, and auxiliary axles the ESC on Vehicle G commanded Compared to the steering wheel loaded to, or very close to, their higher steer axle braking pressures than angles that were derived for the three respective GAWRs. The only exception the ESC on Vehicle I. Vehicle I appeared VRTC tractors, a much wider range in was the 140-inch wheelbase 4x2 which to have more lateral sliding in the SWA was seen among EMA’s results. only had 9,950 lb on the steer axle, maneuver, as its yaw rate decay was The steering wheel angles generally although it was rated for 12,000 lb. slower at the end of steering input. increased with the tractor’s wheelbase In the tests, the stability control Vehicle B (140-inch wheelbase 4x2) from an angle of 126 degrees for the 140- systems automatically applied the exhibited yaw instability in the SWD inch wheelbase 4x2 to an angle of 291 tractor’s foundation brakes to reduce maneuver. This tractor had high lateral degrees for the 270-inch wheelbase 6x4 speed and lateral acceleration. The acceleration that was attained at lower with a pusher axle. For Vehicle H, EMA initial vehicle deceleration generally steering wheel angles than for the 6x4 also provided data from direct coincided with the end of ramp steer tractors. For example, the peak tractor measurement of the steering wheel input, indicating that the stability lateral acceleration was already reaching angle from driving the tractor at 0.5g of control systems were effective at 0.70g at 80 percent of the SIS-derived lateral acceleration. This angle was 290 reducing the lateral acceleration. The steering wheel angle, compared to degrees, which is slightly larger than the speed at wheel lift for EMA’s tests Vehicle I which reached 0.60g and calculated value of 281 degrees ranged from 33 to 38 mph, as compared Vehicle G which reached 0.45g at this extrapolated from the SIS test data in to 31 to 39 mph for the VRTC tests that steering wheel angle scalar. The yaw the 0.05 to 0.30g operating region. The used a similar unbraked trailer, but with rate decay after completion of steer was EMA data provided for these SIS tests a higher center of gravity loading also much slower than for the 6x4 did not include information on stability condition and a higher overall vehicle tractors, which appears to indicate that control engine torque reduction. test weight. Both 4x2 tractors tested by the vehicle was sliding much more and Additional SIS tests were conducted EMA experienced oversteer in addition taking longer to return to the straight- on three tractors that were to be to the wheel lift. ahead position. This is most evident in subsequently tested using the SWD the testing at 130 percent of the SIS- maneuver to evaluate tractor yaw 3. Sine With Dwell Maneuver derived steering wheel angle, in which stability. The SIS test conditions were EMA provided test results for the the decay yaw rate decay was about 3.5 identical to the prior SIS tests. A best fit SWD maneuver for four tractors seconds. linear regression was used to project the equipped with ESC systems. The The maneuver entrance speed was sinusoidal steering frequency used for reduced to 30 mph in the bobtail SWD 27 Data from Vehicles A through I are included testing was 0.5 Hz and the dwell time tests, which were conducted on a low- have been placed in the docket. Docket Nos. was one second. The amplitude of the friction wet Jennite surface. The short NHTSA–2010–0034–0011 through NHTSA–2010– 0034–0021 and Docket No. NHTSA–2010–0034– steering wheel inputs started at 30 wheelbase 4x2 tractor, Vehicle B, 0024. Vehicle J testing is discussed in detail in a percent of the steering wheel angle appeared to complete all of the test later section. derived from SIS testing, and in series without any observed instability

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or control issues, and the peak tractor data show that this was always slightly different. The two 4x2 tractors lateral acceleration was limited to accompanied by braking on the steer (one with RSC, and one with ESC) approximately 0.3g in all tests. axle, which is indicative of oversteer tested by EMA experienced oversteer However, both 6x4 tractors (Vehicles G corrections being commanded by the and wheel lift, while the other tractors and I) appeared to have steering ESC. Vehicle B had much less increase all experienced wheel lift. responsiveness issues that were in lateral acceleration at the end of the SWD test results were provided for particularly noticeable at higher steering maneuver and appeared to be under three tractors, each equipped with ESC, wheel angles. At the reversal in steering control. Late in the maneuver the using a 0.5 Hz sinusoidal steering input wheel angle direction, the yaw rate and commanded brake pressures for Vehicle frequency and a 1.0 second dwell time, lateral acceleration response was B showed that both front and rear brake and the tractors were tested in the delayed, indicating severe understeer. applications were made on the right bobtail condition and loaded to 60 During the dwell portion of the side of the tractor, and the application percent of drive axle(s) GAWR. In the maneuver at higher steering wheel pressures were nearly identical. tests on dry pavement at a maneuver angles, Vehicle I slowly built lateral Whether this is a data collection entrance speed of 45 mph, the typical acceleration up to 0.3g, while Vehicle G anomaly or stability control braking 6x4 completed all tests, while the 6x4 achieved similar but slightly lower strategy is not certain, but Vehicle B was equipped with a lift axle (tested in the acceleration levels. Vehicle G’s yaw rate the vehicle that exhibited the least lowered position) also completed all also was slower to respond at the amount of oversteer. tests but appeared to be slower to completion of steer, taking as long as 2.5 The RWD test results demonstrated respond to the steering inputs. The short seconds to decay to zero for the test that the stability control systems on wheelbase 4x2 tractor appeared to conducted at the highest steering wheel these tractors correctly identified the exhibit control problems and at the angle tested. vehicle loss of control problems (severe highest steering wheel angle tested. The oversteer and understeer) and took sine with dwell tests on the three 4. Ramp With Dwell Maneuver corrective action, including engine tractors in the bobtail condition were The three tractors equipped with ESC output torque intervention and conducted on a low-friction wet Jennite systems tested in the SWD maneuvers commanding individual applications of test surface with a lower maneuver were also tested to the RWD maneuver. the tractor’s foundation brakes. entrance speed of 30 mph. In these tests, Once the initial steering wheel angle However, the severity of the RWD test the short wheelbase 4x2 tractor and test speed were attained, the maneuver was sufficiently high to completed all tests, while the two 6x4 steering machine increased the steering overdrive the capability of the stability tractors appeared to experience severe wheel angle to 180 degrees in one control systems to mitigate severe understeer at the higher steering wheel second, held that steering wheel angle understeer. angles tested. constant for three seconds (the dwell In summary, EMA provided test data portion of the maneuver), and then for nine tractors each tested for the three 5. Vehicle J Testing reduced the steering wheel angle to zero maneuvers developed by NHTSA (a) EMA Testing of Vehicle J in one second. In subsequent RWD test researchers. The nine tractors included In December 2010, EMA provided runs, the steering wheel angle was a wider variety of tractor configurations testing data on a tenth vehicle they increased in 90 degree increments up to than those tested by the agency, and tested.28 Vehicle J was intended to be 540 degrees. included severe service tractors, tractors representative of a typical 6x4 tractor, The test results show that for Vehicles with auxiliary lift axles, a tridem drive with a 245 inch wheelbase and a GVWR B and I, the steady-state lateral axle tractor, and a very short wheelbase of 52,350 pounds. EMA subjected acceleration (prior to the ramp steer) two-axle tractor. Slowly increasing steer Vehicle J to four different test was approximately 0.2g, and for Vehicle vehicle characterization tests were maneuvers: The slowly increasing steer G the steady-state tractor lateral conducted on all nine tractors (two with test; the sine with dwell test; a J-turn acceleration was approximately 0.1g. RSC and seven with ESC) in the bobtail maneuver, and a wet Jennite drive When the steering wheel angle was condition and the test data were used to through test. increased during the initial steering extrapolate the steering wheel angle that EMA first conducted the slowly ramp input, the lateral acceleration and would provide 0.5g of lateral increasing steer test maneuver with a yaw rate increased slightly and in many acceleration at 30 mph. These data steering controller on Vehicle J to of the test runs was then observed to produced a wider range of steering determine the steering wheel angle that drop off, indicating that the tractor was wheel angles than had been seen from would produce a lateral acceleration of not responsive to the steering input. the agency’s tests on its three tractors, 0.5g. EMA conducted two series of test During the first two seconds of the with the short wheelbase 4x2 having an runs, one in each direction. A best fit steering dwell portion of the maneuver, angle of only 116 degrees, and a 6x4 linear regression was used to determine the tractor lateral acceleration typically tractor with a liftable pusher axle having that the average steering angle on the six remained at 0.25g or less for all tests. the highest angle at 291 degrees. runs that would produce a lateral During the last one second of the EMA provided ramp steer maneuver acceleration of 0.5g was 197 degrees. steering dwell, all of the test runs for test results for eight tractors that were This value was used for subsequent Vehicles G and I showed steadily loaded to their GVWRs using an testing. increasing lateral acceleration, as high unbraked 28-foot control trailer. Data EMA next conducted sine with dwell as 0.5g, even as the steering wheel angle were only provided for tests with the testing. EMA conducted two series of was reduced to zero. This indicates that stability control system enabled, and the SWD tests—one with the ESC system on the tractors were in a severe oversteer RSM was conducted up to speeds at and one with the ESC system off. EMA condition, and the agency speculates which the system could successfully equipped the vehicle with an FMVSS that the relatively high lateral intervene. The range of speeds achieved No. 121 control trailer and loaded the acceleration may have been a result of at the point of overdriving the stability the tractor running off of the low control systems was similar to the range 28 Vehicle J data provided to the agency has been friction wet Jennite surface and onto a of speeds from the VRTC RSM tests, placed in Docket No. NHTSA–2010–0034–0022 and higher friction road surface. The test although the loading conditions were Docket No. NHTSA–2010–0034–0023.

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vehicle so that the drive axles were comparison to the test run with the speeds of 30 to 36 mph, in increments loaded to 60 percent of the GAWR, system off (over 0.8g). Momentary of two mph. which resulted in the vehicle being variability in lateral acceleration was In tests conducted with the ESC loaded to approximately 78.6 percent of observed in both tests, indicating system enabled, system activation its GVWR. possible tractor instability. Again, with occurred at each test speed. The system EMA provided data on six runs of the the system on, the lateral acceleration commanded brake activations to reduce SWD maneuver. EMA conducted the decayed faster at the completion of steer vehicle speed to 18 mph from initial test at scalars from 0.8 to 1.3 of the SIS- (approximately 0.4 seconds) than it did speeds of 30 mph and 32 mph, down to derived steering wheel angle. EMA also with the system off (over 0.6 seconds). 10 mph from an initial speed of 34 mph, provided data on three runs of the SWD This was largely due to the reduction in and down to 6 mph at an initial speed maneuver with the system deactivated. lateral acceleration starting later with of 36 mph. The vehicle was able to Those tests were conducted at scalars of the system off than with the system on. maintain the lane at all speeds tested. 1.0 and 1.3, and 1.5. The yaw rate peaked for both tests at Lateral acceleration peaked at 0.4 to 0.5g Each test run with the system enabled approximately 25 degrees per second. at 30 and 32 mph and peaked at 0.6g at showed a 20- to 25-mph reduction of Again, however, the yaw rate decreased 34 mph and 36 mph. Yaw rate peaked speed during the test maneuver. In by approximately five degrees during at approximately 15 degrees per second contrast, tests conducted with the the dwell portion of the maneuver with at 30 and 32 mph and peaked at system off indicated only limited speed the system on while no clear decay was approximately 20 degrees per second at reduction of less than five mph. This observed with the system off. Also, the 34 mph and 36 mph. At the higher indicated that the ESC system acted to yaw rate decreased to zero slower after speeds tested, lateral acceleration and reduce vehicle speed. completion of steer with the system off yaw rate were observed to drop Each test run with the system enabled (0.25 seconds) than it did with the coincident with speed. conducted at scalars between 0.8 and system on (less than 0.2 seconds). With the system disabled, no 1.2 resulted in a peak lateral EMA also submitted data on one SWD reduction in speed during the maneuver acceleration between 0.6g and 0.7g. The test run with the system off at a steering was observed. Thus, lateral acceleration lateral acceleration then quickly wheel angle scalar of 1.5. Peak lateral and yaw rates remained relatively dropped to zero within 0.3 to 0.4 acceleration observed during this test constant throughout the maneuver. At seconds after the completion of the run was nearly 0.9g. The lateral test speeds of 30 and 32 mph, lateral steer. Yaw rate during the dwell portion acceleration rate dropped to zero in acceleration peaked at approximately of the maneuver peaked at slightly over 0.5 seconds after approximately 18 to 22 degrees per 0.55 to 0.65g and yaw rate peaked at completion of steer. The yaw rate approximately 20 degrees per second. second, except at a scalar of 1.2 where peaked at approximately 24 degrees per yaw rate peaked at approximately 24 At 34 mph, the lateral acceleration second. Unlike in runs with lower peaked at approximately 0.9g and the degrees per second) and showed a steering wheel angles, a reduction in steering wheel angle necessary to downward trend during the dwell, yaw rate was observable during the maintain the lane decreased dropping by approximately five degrees dwell portion. However, that reduction substantially. Yaw rate peaked at per second. The yaw rate dropped to was much sharper, occurring entirely approximately 22 degrees per second zero within 0.2 seconds after within a 0.5 second period rather than and dropped to approximately 15 completion of steer. The vehicle’s ESC throughout the entire 1.0 second dwell degrees per second, indicating the system used selective braking to reduce period. Like in prior tests, the yaw rate vehicle was starting to plow out. At 36 the speed, lateral acceleration, and yaw dropped to zero within approximately mph, the vehicle plowed out of the lane. rate responses. 0.25 seconds. With the system disabled, the test run EMA’s SWD maneuver test data from The fourth maneuver EMA performed at a scalar of 1.0 resulted in a peak Vehicle J demonstrated that the ESC on Vehicle J was a wet Jennite drive- lateral acceleration of approximately system activated to lower lateral through (WJDT) maneuver. This 0.8g. A 0.2g drop in lateral acceleration acceleration and yaw rate during the maneuver was intended to test yaw was observed at the beginning of the SWD maneuver. However, even with the stability. The WJDT maneuver is dwell portion of the maneuver followed ESC system turned off, the lateral identical to method for determining the by a sudden rise of the same amount, acceleration and yaw rates dropped maximum drive-through speed when indicating possible oversteer. The lateral relatively quickly at the end of the test testing vehicles for compliance with acceleration dropped to zero less maneuver, indicating that the vehicle S5.3.6.1 of FMVSS No. 121. The vehicle quickly than in tests with the system on did not become unstable during testing. is driven through a 500-foot radius (approximately 0.5 seconds) after Although EMA only provided test data curve with a wet surface having a peak completion of steer. This was largely from three runs with the system off coefficient of friction of approximately due to the drop in lateral acceleration compared to six runs with the system 0.5 at successively increasing speeds starting later with the system off than enabled, the runs with the system off (up to 40 mph) to determine the with the system on. The yaw rate did include a run with a steering wheel maximum speed at which the vehicle peaked at approximately 21 degrees per angle scalar of 1.5, which was higher can maintain the curve.29 second. Unlike with the system on, than any run in NHTSA’s testing, and EMA performed this test with both there was not a clear drop in yaw rate no severe incidents of instability were the stability control system enabled and during the dwell portion of the observed. disabled in two load configurations. maneuver. The yaw rate also dropped to EMA next conducted J-turn testing First, the vehicle was tested in the zero slower than in tests with the both with the system enabled and bobtail (unloaded) configuration. system off (approximately 0.25 seconds disabled. The test was conducted on a after completion of steer). 150-foot fixed radius curve. The vehicle 29 To conduct the FMVSS No. 121 stability and For test runs at steering wheel angle was tested with an FMVSS No. 121 control during braking compliance test, the vehicle is driven at the lesser of 30 mph or 75 percent of scalars of 1.3, the peak lateral control trailer and was loaded to the the maximum drive-through speed. A full brake acceleration was slightly lower with the FMVSS No. 121 loading conditions. The application is made and a vehicle must stop at least system on (approximately 0.75g) in tests were conducted at initial entry three times out of four within the 12-foot lane.

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Second, the vehicle was loaded to the 34 mph with the system on. This First, EMA’s control trailer had a wider FMVSS No. 121 test loading condition. demonstrates that an ESC system has track width 33 than NHTSA’s trailer, In the bobtail configuration with the some ability to mitigate understeer which made EMA’s trailer, and thereby ESC system enabled, test runs at 30 and when navigating a curve on a low- the combination vehicle, more stable 32 mph yielded no system activation. At friction surface, and allow the driver to during SWD testing. Second, EMA’s 33 mph, system activation occurred as maintain control at higher curve control trailer had a lower deck height both engine torque reduction and entrance speeds. than NHTSA’s trailer, which selective braking to improve yaw contributed to a lower center of gravity stability occurred. As a result, the (b) NHTSA Testing of EMA’s Vehicle J on EMA’s trailer. Third, EMA loaded its vehicle speed decreased to At NHTSA’s request, EMA provided trailer with steel for ballast, whereas approximately 29 mph during the Vehicle J to NHTSA for NHTSA to NHTSA loaded its trailer with concrete maneuver and the driver responded by duplicate EMA’s testing.30 In particular, for ballast, which also contributed to the rapidly straightening the steering wheel. the agency was interested in the lower center of gravity on EMA’s trailer Vehicle yaw rate peaked at performance of Vehicle J during the sine because steel would not have to be approximately 10 degrees per second. A with dwell maneuver. NHTSA’s two 6x4 stacked as high to achieve a full load. second run at 33 mph showed only brief tractors that were tested in with the E. Other Industry Research system activation and a minimal SWD represented the upper and lower reduction in speed. During two runs at size bounds of what would be The SAE Truck and Bus Control 34 mph, ESC system intervention was considered a typical 6x4 tractor and Systems Task Force (renamed as the again observed as torque reduction and both tractors could not maintain Truck and Bus Stability Control selective braking reduced vehicle speed stability during a SWD maneuver with Committee) was formed in 2007 to to 28 to 29 mph and the driver again the ESC system disabled. Vehicle J’s size facilitate information sharing among the responded by rapidly straightening the is within the bounds of the two typical industry and government regarding steering wheel. Yaw rate peaked at near 6x4 tractors tested by NHTSA. heavy vehicle stability control 34 10 degrees per second and again, as the NHTSA conducted 20 test runs of systems. The information shared driver responded, decreased. During Vehicle J in the SWD maneuver at included proposed test maneuvers that two runs at 35 mph, the vehicle was steering wheel angle scalars of 0.4 to 1.3 could potentially be used to evaluate the unable to maintain the lane due to of the SIS-derived steering wheel angle performance of stability control systems. understeer, despite system intervention. attached to VRTC’s FMVSS No. 121- Although the Task Force has not In the bobtail configuration with the style control trailer. When tested with published any formal documents system disabled, at 32 mph, the driver the ESC system disabled at a steering describing these test maneuvers, the had to adjust steering by adding steering wheel angle scalar of 1.2, NHTSA was following provides an overview of the input during both runs attempted at this able to detect lateral instability that maneuvers that have been discussed. speed, indicating substantial understeer. continued for almost two seconds after 1. Decreasing Radius Test During two runs at 33 mph, the vehicle completion of the SWD maneuver.31 was unable to maintain the lane, despite A decreasing radius test (DRT) was It was discovered that EMA developed to evaluate the roll stability large steering inputs from the driver. conducted its testing of Vehicle J with In the loaded configuration with the performance of a heavy vehicle stability a control trailer with different ESC system enabled, system activation control system.35 With the DRT, the test specifications than NHTSA used. occurred at a speed of 30 mph, though conditions could also be adjusted to NHTSA then attempted to duplicate only slight (1 to 2 mph) reduction in evaluate yaw stability as well. In the EMA’s Vehicle J’s testing using the speed was observed. The driver had to DRT, the vehicle is accelerated to a control trailer used by EMA.32 The increase his steering input, but there constant speed of 29 mph on a dry road results of NHTSA’s tests with EMA’s was no corresponding increase in yaw surface, and an initial steering input is control trailer were not meaningfully rate, indicating understeer. At 32 mph, made to follow a curve with a 150-foot different than the results of EMA’s both engine torque reduction and radius. Once the initial curve radius is testing. That is, there were no instances selective braking occurred to improve achieved, the radius is linearly reduced of substantial roll or yaw instability in yaw stability occurred. As a result, the to a radius of 90 feet as the vehicle 20 test runs conducted by NHTSA. vehicle speed decreased to negotiates 120 degrees of arc. Thus, it is As a result of NHTSA’s testing of approximately 27 to 28 mph during the similar to the J-turn maneuver. The Vehicle J, the agency discovered that maneuver. At 34 mph, the ESC system speed of 29 mph was derived based on there exist three areas of variability in intervened more substantially, resulting a vehicle dynamics simulation, which FMVSS No. 121-style control trailers in a reduction of speed to approximately estimated that the maneuver would and loading which, while not 26 mph. Nevertheless, the vehicle was produce 0.3g of lateral acceleration necessarily relevant to FMVSS No. 121 able to maintain the lane. At 35 mph, during the initial steering input and this testing, could affect the results of the vehicle was unable to maintain the would steadily increase to 0.6g at the stability control system testing if the lane due to understeer, despite system 90-foot radius curve. specifications for an FMVSS No. 121- intervention. Tests would be conducted in a loaded In the loaded configuration with the style control trailer were simply carried condition with the tractor coupled to a system disabled, understeer was over to a stability control standard. trailer and an unloaded condition in a

observed at 32 mph, as evident by 30 substantial increase in steering input by A copy of NHTSA’s Vehicle J test data has been 33 The track width is the distance between the placed in the docket. Docket No. NHTSA–2010– centerlines of a vehicle’s left and right tires. In the driver; however, the vehicle was 0034–0044. vehicles with dual tires, the track width would be able to maintain the lane. At 33 mph, 31 NHTSA was able to conduct 19 test maneuvers measured from between the dual tires on each side the vehicle was unable to maintain the with Vehicle J that did not result in substantial roll of the vehicle. lane. instability. NHTSA did not find any yaw instability 34 See http://www.sae.org/events/cve/ in any of the 20 test maneuvers. presentations/2007truckbus.pdf for an overview of The maximum drive through speed in 32 NHTSA’s test data identifies the trailer used by the SAE Truck and Bus Council organizational both vehicle configurations was only 32 EMA as a ‘‘Link’’ trailer and the trailer used by chart. mph with the system off, compared to NHTSA as the ‘‘NHTSA’’ or ‘‘VRTC’’ trailer. 35 See Docket No. NHTSA–2010–0034–0036.

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bobtail configuration. Because actual in the bobtail condition using a low- on a large diameter circle and sinusoidal vehicle testing had not been conducted friction wet Jennite road surface steering, can be used to demonstrate using this maneuver, pass/fail criteria (nominal peak friction coefficient of that a stability control system is capable have not yet been developed. 0.5). The vehicle is driven at a constant of preventing a rollover or a yaw Simulations of this test have been run speed of approximately 30 mph and, as instability condition. The RWD using driver-controlled steering inputs; a sinusoidal steering input is initiated maneuver may exceed the capabilities of however, parameters could also be (continuous left and right steering stability control systems but provides developed to conduct this maneuver inputs using the steering wheel angle brake application data that can be using an automated steering controller. determined above), the driver increases reviewed to determine if a stability the throttle position to request 100 control system provides the correct 2. Lane Change on a Large Diameter percent of engine torque. control responses to address a severe Circle The second test maneuver developed oversteer or understeer condition. Volvo provided information on the by Bendix was the ramp with a dwell Lane Change on a Large Diameter Circle maneuver discussed in section IV.D.4 V. Agency Proposal (LC–LDC) maneuver that they have used above.38 The RWD maneuver is Based upon the foregoing research, to evaluate stability control system intended to evaluate understeer the agency is proposing a new FMVSS performance.36 In this maneuver the prevention, though oversteer can also to require ESC systems be installed on vehicle is driven at a constant speed, occur during the maneuver. The RWD truck tractors and buses with a GVWR just below the threshold speed for test is conducted with the tractor in the of greater than 11,793 kilograms (26,000 rollover or loss of control, around the bobtail condition and using a wet pounds).39 There are several issues inside lane of an 800-foot radius curve Jennite road surface. The first step in raised by this proposed rule on which that has two lanes. The driver then this test is to characterize the vehicle’s the agency seeks public comment, each drifts to the outside lane, and steers steering by conducting a series of drive- of which is discussed in detail in the back into the inside lane. For rollover through speed evaluations at a constant following sections. testing the asphalt road surface is dry speed on a 500-foot radius curve. Once A. NHTSA’s Statutory Authority and for yaw testing the surface is wet. the maximum constant travel speed is The test can be conducted using a determined (typically between 28 and NHTSA is proposing today’s NPRM bobtail tractor, a tractor towing an 32 mph, but not to exceed 35 mph), the under the National Traffic and Motor FMVSS No. 121 control trailer, or a steering wheel angle is measured for Vehicle Safety Act (‘‘Motor Vehicle tractor towing any other type of trailer negotiating the curve at that speed. The Safety Act’’). Under 49 U.S.C. Chapter in a fully loaded condition. Volvo RWD test maneuver speed is then 301, Motor Vehicle Safety (49 U.S.C. evaluated the roll stability performance conducted at the maximum drive- 30101 et seq.), the Secretary of during this maneuver based on whether through speed. Bendix suggested that Transportation is responsible for the trailer outrigger made contact with manual steering by a test driver or an prescribing motor vehicle safety the ground. Volvo considers this automated steering machine could be standards that are practicable, meet the maneuver to be representative of certain used. Once the vehicle has been need for motor vehicle safety, and are highway segments that are encountered, accelerated to the test maneuver speed, stated in objective terms. ‘‘Motor vehicle and that the maneuver is severe enough the speed is held constant by the driver safety’’ is defined in the Motor Vehicle to fully challenge a stability control and he inputs the drive-through steering Safety Act as ‘‘the performance of a system. wheel angle. After the vehicle reaches a motor vehicle or motor vehicle constant lateral acceleration condition, equipment in a way that protects the 3. Yaw Control Tests the steering wheel angle is increased to public against unreasonable risk of Bendix developed two yaw stability 180 degrees in a period of one second. accidents occurring because of the test maneuvers to evaluate the ability of That increased angle is held constant for design, construction, or performance of stability control systems to prevent three seconds, and then the angle is a motor vehicle, and against severe oversteer and understeer reduced to zero in a period of one unreasonable risk of death or injury in conditions. The first test maneuver is a second. Subsequent test runs are an accident, and includes Sinusoidal Steering Maneuver (SSM) to conducted by increasing the steering nonoperational safety of a motor evaluate oversteer prevention.37 The wheel angle in increments of 90 degrees vehicle.’’ ‘‘Motor vehicle safety first step in this test is to identify the up to 540 degrees. standard’’ means a minimum steering wheel angle that produces a The RWD test performance measures performance standard for motor vehicles tractor lateral acceleration of 0.5g at 30 would be based upon test data showing or motor vehicle equipment. When that the vehicle’s stability control mph on dry pavement with the tractor prescribing such standards, the system successfully identified a vehicle in the bobtail condition. Bendix Secretary must consider all relevant, control problem (understeer or recommended that this angle be derived available motor vehicle safety oversteer) and intervened by reducing by either a slowly increasing steer test information. The Secretary must also the engine torque output and (SIS test described in section IV.D.2 consider whether a proposed standard is commanding the application of above) or an equation developed by reasonable, practicable, and appropriate individual foundation brakes in a Bendix for estimating the angle based on for the types of motor vehicles or motor manner that is suitable to mitigate the the tractor’s wheelbase: vehicle equipment for which it is control problem. Bendix did not believe Steering Wheel Angle (d) = (35.5 × prescribed and the extent to which the that vehicle yaw or path-following pass/ (tractor wheelbase in meters)) + standard will further the statutory fail criteria would be appropriate for 30.94 purpose of reducing traffic accidents this test maneuver. and associated deaths. The The Sinusoidal Steering Maneuver Two maneuvers that the industry has test is then conducted with the tractor developed to evaluate the performance 39 To distinguish this new FMVSS from the light of stability control systems, lane change vehicle ESC requirement in FMVSS No. 126, we are 36 See Docket No. NHTSA–2010–0034–0042. proposing to revise the title FMVSS No. 126 to 37 See Docket No. NHTSA–2010–0034–0037. 38 See Docket No. NHTSA–2010–0034–0038. reflect that it is applicable only to light vehicles.

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responsibility for promulgation of of this proposed requirement to be concrete trucks, refuse trucks, and other Federal motor vehicle safety standards similar to the applicability of the air-braked trucks, and that the same is delegated to NHTSA. In making the agency’s proposal that certain buses be technology could be developed for use proposals in today’s NPRM, the agency equipped with seat belts.40 That on Class 7 buses, which we believe are carefully considered all the proposal was applicable to buses with a also air-braked vehicles. aforementioned statutory requirements. gross vehicle weight rating (GVWR) of Although this proposal would not 11,793 kilograms (26,000 pounds) or apply to all buses with a GVWR of B. Applicability greater, 16 or more designated seating greater than 11,793 kilograms (26,000 1. Vehicle types positions (including the driver), and at pounds), we seek comment on whether this proposal should be applied to the Vehicles with a GVWR greater than least 2 rows of passenger seats that are rearward of the driver’s seating position types of buses that are excluded from 10,000 pounds include a large variety of and are forward-facing or can convert to the proposed rule such as school buses vehicles ranging from medium duty forward-facing without the use of tools.’’ and transit buses. We also seek pickup trucks to different types of single That proposal excluded school buses comment on the feasibility of including unit trucks, buses, trailers and truck and urban transit buses sold for the Class 7 buses described in the prior tractors. Vehicles with a GVWR of operation in urban transportation along paragraph that are built on chassis greater than 10,000 pounds are divided a fixed route with frequent stops. The similar to those of single unit trucks into Classes 3 through 8. Class 7 agency is proposing a very similar within two years. In particular, we vehicles are those with a GVWR greater applicability in this NPRM. We have not believe that ESC systems are readily than 11,793 kilograms (26,000 pounds) made this proposal applicable to buses available for air-braked buses; however, and up to 14,969 kilograms (33,000 with a GVWR of exactly 11,793 system availability for any hydraulically pounds), and Class 8 vehicles are those kilograms (26,000 pounds) in order to braked buses that may be covered by with a GVWR greater than 14,969 exclude Class 6 vehicles from this this proposed rule may be more limited. kilograms (33,000 pounds). proposal. We believe that this proposal If hydraulically braked buses are The vast majority of vehicles with a encompasses the category of ‘‘cross- covered by this proposal, we request GVWR of greater than 4,536 kilograms country intercity buses’’ represented in comment on manners in which (10,000 pounds) for which stability the FARS and FMCSA data (identified hydraulically braked buses may be control systems are currently available in section II.A above) that had a higher differentiated for exclusion or a are truck tractors. Approximately involvement of crashes that ESC different phase-in period. 150,000 truck tractors with a GVWR of systems are capable of preventing. The agency is not proposing to greater than 11,793 kilograms (26,000 The agency tested three buses, all of include single unit trucks with a GVWR pounds) are manufactured each year. In which had a GVWR over 14,969 kg over 4,536 kg (10,000 pounds) at this 2009, about 20 percent of Class 7 and 8 (33,000 pounds). There are seven time. There are substantial differences truck tractors were equipped with a manufacturers or distributors of Class 8 in the complexity of the single unit stability control system. buses covered by this proposal for the truck population compared to the truck- About 85 percent of truck tractors U.S. market: Prevost, MCI, VanHool, tractor population. The single unit truck sold annually in the U.S. are air-braked Daimler/Setra, CAIO, BlueBird, and BCI. population has wide variations in three-axle (6x4) tractors with a front Three of them (Prevost, MCI, and vehicle weight, wheelbase, number of axle that has a GAWR of 14,600 pounds VanHool), have stated that an ESC axles, center of gravity height, and cargo or less and with two rear drive axles system is a standard feature on their type, among other things that affect the that have a combined GAWR of 45,000 buses sold in the U.S. Daimler/Setra calibration and performance of stability pounds or less, which we will refer to indicated that an ESC system will be control systems. While some variation as ‘‘typical 6x4 tractors.’’ Two-axle (4x2) available as an option on its buses exists in the truck tractor market, the tractors and severe service tractors beginning in model year 2011 and that degree of complexity and diversity is (those with three axles that are not no decision has been made to make it substantially less. ‘‘typical 6x4 tractors’’ or those with four a standard feature. No official Further, the single unit truck market or more axles) represent about 15 information is available from CAIO, is structurally different than the truck percent of the truck-tractor market in Bluebird, and BCI regarding ESC system tractor market in that the chassis the U.S. availability. supplier, who is generally responsible The majority of the research on the There are also at least nine for the brake systems and therefore effectiveness of stability control systems manufacturers of Class 7 buses covered would likely provide stability control to date has been performed on typical by this proposal for the U.S. market: systems, is often different than the final 6x4 tractors. As a result, the agency’s Champion, ElDorado National, Federal body builder. Hence, the chassis research included two typical 6x4 Coach, Glaval, IC Bus, MCI, Rexhall, supplier may not have knowledge of tractors. The agency also included one Stallion, and VanHool. Many Class 7 critical vehicle design parameters that 4x2 tractor in its testing because two- buses are built on chassis similar to would affect stability control system axle tractors represent the next largest those of single unit trucks for which calibration. In contrast, manufacturers segment of the truck-tractor market. No ESC has not been widely developed, of truck tractors have more complete severe service tractors were tested. EMA and we are not aware of any Class 7 bus control of the final, delivered vehicle. performed tests on nine tractors that is equipped or currently available The complexity of the single unit equipped with stability control systems. with ESC. Class 7 buses represent less truck population and the limited crash The tractors included two 4x2 tractors, than 20 percent of the market. Although data available present a significant two typical 6x4 tractors, two severe the agency is not aware of any Class 7 challenge to determining the service 6x4 tractors, two 6x4 tractors bus currently available with ESC, we are effectiveness of stability control on with a liftable auxiliary axle in front of aware that stability control systems are these vehicles. We believe that the drive axles, and one 8x6 tractor. available on a limited number of Class approximately 1 percent of newly This proposal would also require 8 single unit trucks, such as ready mix manufactured single-unit trucks are certain buses to be equipped with an equipped with stability control systems, ESC system. We intend the applicability 40 75 FR 50,958 (Aug. 18, 2010). and that few, if any, of those are for

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vehicles with hydraulic brakes. The Therefore, the agency proposes to tires and brake components that are development of stability control system require stability control systems on important for ESC performance. for vehicles over 10,000 pounds GVWR truck tractors and buses with a GVWR • The original manufacture date of has been focused on air-braked vehicles, of greater than 11,793 kilograms (26,000 vehicles that should be subject to any which include the truck tractors and pounds). retrofitting requirements. buses addressed in this proposal. • Whether the performance 2. Retrofitting In-Service Truck Tractors, Because we are concerned about the requirements for retrofitted vehicles Trailers, and Buses availability of production-ready systems should be less stringent or equally on these vehicles, they are not included NHTSA has considered proposing to stringent as for new vehicles, and, if less in the proposal. However, we seek require retrofitting of in-service truck stringent, the appropriate level of comment on these observations. tractors, trailers, and large buses with stringency. The agency has initiated a safety stability control systems proposed to be • The cost of retrofitting a stability benefit study to determine the safety required by this NPRM. The Secretary control system on a vehicle, which we need for stability control on single-unit has the statutory authority to believe would exceed the cost of trucks, and has also initiated vehicle promulgate safety standards for including stability control on a new research, similar to the research ‘‘commercial motor vehicles and vehicle. conducted on truck tractors and large equipment subsequent to initial In light of these questions, the agency buses described in part IV.C above, manufacture.’’ 41 The Secretary has is not proposing that in-service vehicles which is expected to be completed in delegated authority to NHTSA to be required to be retrofitted with 2012. However, the agency proposes to ‘‘promulgate safety standards for stability control systems. Instead, this require stability control systems on commercial motor vehicles and proposed requirement would be truck tractors without waiting for the equipment subsequent to initial applicable only to newly manufactured study on the effectiveness of stability manufacture when the standards are vehicles. However, the comments we control systems on single-unit trucks to based upon and similar to [an FMVSS] receive on the issue of retrofitting will be completed. Waiting for that study to promulgated, either simultaneously or help us determine whether we should be completed would unnecessarily previously, under chapter 301 of title issue a separate supplemental NPRM to delay the benefits of having stability 49, U.S.C.’’ 42 Additionally, the Federal require a retrofit. control systems on truck tractors and Motor Carrier Safety Administration 3. Exclusions From Stability Control large buses, for which testing has been (FMCSA) is authorized to promulgate Requirement completed the benefits of stability and enforce vehicle safety regulations, Our proposed rule excludes certain control systems identified. including those aimed at maintaining types of low-volume, highly specialized The agency is not proposing to commercial motor vehicles so they vehicle types. In these cases, the include a requirement for stability continue to comply with the safety vehicle’s speed capability does not control systems on trailers, primarily standards applicable to commercial allow it to operate at speeds where roll because trailer-based RSC systems were motor vehicles at the time they were or yaw instability is likely to occur. judged by the agency research to be manufactured. Although this NPRM much less effective than tractor-based Specifically, FMVSS No. 121, Air does not propose requiring truck brake systems, excludes certain heavy RSC or ESC systems in preventing tractors, trailers, or large buses to be rollover. Trailer-based RSC systems are air-braked heavy vehicles from that equipped with stability control systems standard. For truck tractors and buses, capable of applying braking only on the ‘‘subsequent to initial manufacture,’’ we trailer’s brakes. Tractor-based systems these exclusions include: are requesting public comment on • Any vehicle equipped with an axle can command more braking authority by several issues related to retrofitting in- using both the tractor and trailer brakes. that has a gross axle weight rating of service truck tractors, trailers, and 29,000 pounds or more. As a result, trailer-based RSC systems buses: • do not appear to provide additional • Any truck or bus that has a speed The extent to which a proposal to attainable in two miles of not more than safety benefits when used in retrofit in-service vehicles with stability combination with tractor-based RSC or 33 mph. control systems would be complex and • Any truck that has a speed ESC systems. The trailer-based RSC costly because of the integration systems provide some improvement in attainable in two miles of not more than between a stability control system and 45 mph, an unloaded vehicle weight roll stability compared to a base trailer the vehicle’s chassis, engine, and without an RSC system, but a vehicle that is not less than 95 percent of its braking systems. GVWR, and no capacity to carry could still be overdriven at a lower • The changes necessary to an speed with trailer-based RSC systems occupants other than the driver and originally manufactured vehicle’s operating crew. than with a tractor-based system. This systems that interface with a stability means that the maneuver entrance We believe that the vehicles that are control system, such as plumbing for excluded from the requirements of speed beyond which the stability new air brake valves and lines and a control system is unable to reduce the FMVSS No. 121 should also be new electronic control unit for a revised excluded from the proposed stability vehicle speed to prevent a rollover was antilock brake system. lower for the trailer-based system than • control requirements because the speed The additional requirements that at which these vehicles operate would for the tractor-based system. In addition, would have to be established to ensure the typical service life of a trailer is 20 make it unlikely that roll or yaw that stability control components are at instability would occur. Accordingly, to 25 years compared with about 8 to 10 an acceptable level of performance for a years for a truck tractor. Because new the proposed stability control compliance test, given the uniqueness of requirement excludes these vehicles. tractors are added to the U.S. fleet at a the maintenance condition for vehicles faster rate than new trailers, the safety in service, particularly for items such as C. ESC System Capabilities benefits from stability control systems 1. Choosing ESC vs. RSC would be achieved at a faster rate by 41 See Motor Carrier Safety Improvement Act of requiring stability control systems to be 1999, sec. 101(f), Pub. L. 106–159 (Dec. 9, 1999). We are proposing to require that truck installed on a tractor. 42 See 49 CFR 1.50(n). tractors and large buses be equipped

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with ESC systems rather than RSC configurations and operating ranges for phases of driving, including systems. An ESC system is capable of all heavy vehicles, the agency does not acceleration, coasting, deceleration, and of the functions of an RSC system. In believe it is practical to develop braking, except when the vehicle is addition, an ESC system has the performance tests that would address below a low-speed threshold where loss additional ability to detect yaw the full range of possibilities and remain of control or rollover is unlikely. instability, provide braking at front cost-effective. Accordingly, the agency According to information the agency has wheels, and detect the steering wheel is proposing to include a definitional obtained from vehicle manufacturers angle. These additions, as demonstrated requirement in this proposed rule that and ESC suppliers, this low speed by NHTSA’s testing, allow an ESC includes equipment that would be threshold for a stability control system system to have better rollover required as part of a compliant ESC is 10 km/h (6.2 mph) for yaw stability prevention performance than an RSC system. We note that, when developing control and 20 km/h (12.4 mph) for roll system in addition to the yaw instability the ESC requirement for light vehicles, stability control. For the purposes of a prevention component. This is because the agency chose to include such a proposed regulation, we believe that the steering wheel angle sensor allows requirement in FMVSS No. 126. setting a single low speed threshold the ESC system to anticipate changes in SAE International has a would be preferable since the yaw and lateral acceleration based upon driver Recommended Practice on Brake roll stability functions during a test input and to intervene with engine Systems Definitions—Truck and Bus, maneuver are closely intertwined, torque reduction or selective braking J2627 (Aug. 2009), which includes a which could make it difficult to sooner, rather than waiting for the definition of Electronic Stability Control differentiate when the roll or yaw lateral acceleration sensors to detect and Roll Stability Control. SAE function ends. Therefore, we propose a potential instability. International’s definition of an ESC single threshold of 20 km/h (12.4 mph) As discussed in greater length in system requires that a system have an as the speed below which ESC is not Section VI, mandating ESC systems electronic control unit that considers required to be operational. rather than RSC systems will prevent wheel speed, yaw rate, lateral Therefore, the agency proposes to more crashes, injuries, and fatalities. acceleration, and steering angle and that require the installation of an ESC system The additional benefits from ESC the system must intervene and control on truck tractors and large buses, which systems can be attributed to both the engine torque and auxiliary brake has all of the following attributes: ESC’s system’s ability to intervene systems to correct the vehicle’s path. 1. Augments vehicle directional sooner and its ability to prevent yaw The UN ECE Regulation 13 definition stability by applying and adjusting instability that would lead to loss-of- for the electronic stability control vehicle brake torques individually at control crashes. system, promulgated in Annex 21, each wheel position on at least one front Mandating ESC systems rather than includes the following functional and at least one rear axle of the vehicle RSC systems will result in higher costs attributes for directional control: to induce correcting yaw moment to to manufacturers. Moreover, our benefit sensing yaw rate, lateral acceleration, limit vehicle oversteer and to limit and cost estimates lead to the wheel speeds, braking input and vehicle understeer; preliminary conclusion that mandating steering input; and the ability to control 2. Enhances rollover stability by RSC systems would be more cost- engine power output. For vehicles with applying and adjusting the vehicle brake effective than mandating ESC systems. rollover control, the functions required torques individually at each wheel However, these extra costs are more by the stability control include: sensing position on at least one front and at least than offset by higher net benefits that lateral acceleration and wheel speeds; one rear axle of the vehicle to reduce would accrue by mandating ESC and the ability to control engine power lateral acceleration of a vehicle; systems rather than RSC systems. output. 3. Computer-controlled with the In developing a definition for ESC, the 2. Definition of ESC computer using a closed-loop algorithm agency has reviewed the functional to induce correcting yaw moment and Definitional requirements in an attributes contained in the SAE and the enhance rollover stability; FMVSS define and describe the type of ECE definitions, and has incorporated 4. Has a means to determine the system that can be used to meet the portions of both of these definitions in vehicle’s lateral acceleration; performance requirements of a this NPRM. We have developed a 5. Has a means to determine the particular FMVSS. However, the definition that is similar in wording to vehicle’s yaw rate and to estimate its inclusion of a definitional requirement the definition from FMVSS No. 126, side slip or side slip derivative with in an FMVSS may be design restrictive which specifies certain features that respect to time; because it would be based on currently must be present, that ESC be capable of 6. Has a means to estimate vehicle available technology. Limiting the applying all the brakes individually on mass or, if applicable, combination equipment that can be used to satisfy an the vehicle, and that it have a computer vehicle mass; FMVSS may limit future technological using a closed-loop algorithm to limit 7. Has a means to monitor driver advancements and innovation. As vehicle oversteer and understeer when steering input; stability control technologies are appropriate. Unlike the light vehicle 8. Has a means to modify engine developed even further, a definitional standard, which focuses on yaw torque, as necessary, to assist the driver requirement could be a hindrance to stability, this NRPM proposes to require in maintaining control of the vehicle; safety improvements if it limits the use a stability control system that also helps and of a newly developed equipment or to mitigate roll instability conditions. As 9. When installed on a truck tractor, technology that is not addressed by the a result, we have expanded the has the means to provide brake pressure specified definitional requirement. On definition from the one in FMVSS No. to automatically apply and modulate the the other hand, relying solely on 126 to include a requirement that the brake torques of a towed semi-trailer. performance-based tests without system be capable of sensing impending The benefit of an ESC system is that mandating any specific equipment may rollover and reducing the vehicle’s it will reduce vehicle rollovers and loss require a battery of tests to cover the lateral acceleration to prevent rollover. of control under a wide variety of complete operating range of the vehicle. Furthermore, we believe that the ESC vehicle operational and environmental Given the wide array of possible system must be operational during all conditions. However, the performance

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tests proposed in this NPRM would only controls for ESC that would allow a the earliest opportunity in order to evaluate ESC system performance under driver to deactivate or adjust the ESC continue to realize the system’s safety very specific environmental conditions. system. Given the lack of on/off benefits. To ensure that a vehicle is equipped switches on heavy vehicles equipped The ESC malfunction telltale would with an ESC system that meets the with ESC, we do not propose to allow be required to remain illuminated proposed definition, we are proposing an on/off switch for ESC systems in this continuously as long as the malfunction that vehicle manufacturers make NPRM. Nevertheless, we seek comment exists whenever the ignition locking available to the agency documentation on the need to allow an on/off switch. system is in the ‘‘On’’ (‘‘Run’’) position. that would enable us to ascertain that Such comments should address why The ESC malfunction telltale must the system includes the components manufacturers might need this extinguish after the malfunction has and performs the functions of an ESC flexibility and how manufacturers been corrected. These proposed system. would implement a switch in light of requirements are identical to the We are proposing that the vehicle the ABS requirements for truck tractors requirements established in the light manufacturer provide a system diagram and large buses. vehicle ESC standard, FMVSS No. 126, that identifies all ESC system hardware; and help to ensure that the system a written explanation, with logic E. ESC Malfunction Detection, Telltale, provides a warning indication in the diagrams included, describing the ESC and Activation Indicator event of a malfunction. system’s basic operational 1. ESC Malfunction Detection Because many malfunctions cannot be characteristics; and a discussion of the detected when the vehicle is stationary, This proposed rule would require that pertinent inputs to the computer and this NPRM includes a test that would vehicles be equipped with an indicator how its algorithm uses that information allow the engine to be running and the to prevent rollover and limit oversteer lamp, mounted in front of and in clear vehicle to be in motion as part of the and understeer. Because the proposed view of the driver, which is activated diagnostic evaluation. We are aware that definition for ESC systems on truck whenever there is a malfunction that some malfunctions are not time-based, tractors includes the capability to affects the generation or transmission of but instead require comparisons of provide brake pressure to a towed control or response signals in the sensor outputs generated when the vehicle, the agency is proposing to vehicle’s ESC system. Heavy vehicles vehicle is driven. Hence, some require that, as part of the system presently equipped with ESC generally malfunctions would require certain documentation, the manufacturer do not have a dedicated ESC driving motions to make the ESC include the information that shows how malfunction lamp. Instead, they share system’s malfunction detection possible. the tractor provides brake pressure to a that function with the mandatory ABS We believe that an ESC malfunction towed trailer under the appropriate malfunction indicator lamp or the should be detected within a reasonable conditions. traction control activation lamp. The time of starting to drive. As a result, we It is common practice for the agency proposes requiring a separate propose that the malfunction telltale NHTSA’s Office of Vehicle Safety ESC malfunction lamp because it would illuminate within two minutes after Compliance to request relevant alert the driver to the malfunction attaining a test speed of 48 km/h technical information from a condition of the ESC and would help to (30 mph) so that the parts of a system’s manufacturer prior to conducting many ensure that the malfunction is corrected malfunction detection capability that of its compliance test programs. The at the earliest opportunity. depend on vehicle motion can operate. agency included such a requirement in We believe that there are safety This two-minute period is identical to the light vehicle ESC standard. Prior to benefits associated with such a warning. the period included in the test conducting any of the FMVSS No. 126 An ESC malfunction indicator warns the procedure in FMVSS No. 126 for ESC compliance tests, NHTSA requires driver in the event of an ESC system malfunction detection. manufacturers to provide the malfunction so that the system can be We anticipate that FMCSA will issue documentation required by that repaired. ESC system activations on a a companion proposal to NHTSA’s standard, including identification of all heavy vehicle will be infrequent events proposal to require ESC on truck ESC system hardware and an in panic situations, and drivers should tractors and large buses, which would explanation of the system operational not experience the activation of a require that the ESC system on a characteristics. We also request stability control system during the commercial vehicle be maintained in a additional information about the ESC normal operation of the vehicle. fully operating condition. In addition, system including manufacturer make Because most steering maneuvers we expect that the roadside inspection and model, telltale(s), pertinent owner’s performed during the normal operation procedures developed for commercial manual excerpts and suggested of a heavy vehicle are not severe enough vehicle ESC systems would be malfunction scenarios. All of the to activate the ESC system, a vehicle facilitated by the ESC malfunction requested information allows NHTSA to may be operated for long periods telltale and the format that is required verify that the ESC system meets the without an ESC activation event. to indicate whether or not the system is definitional and operational Without such a malfunction indicator, a operational. requirements that cannot necessarily be driver might have no way of knowing 2. ESC Malfunction Telltale verified during the performance test. that an ESC system is malfunctioning Furthermore, this information aids the until a loss of control or rollover event The ESC malfunction lamp test engineers with execution and occurs. For example, the agency requirement in this NPRM states that completion of the compliance test. received a complaint recently in which each truck tractor and large bus must be a heavy truck had an inoperative ESC equipped with a telltale that provides a D. ESC Disablement system, but the driver was unaware of warning to the driver when one or more The agency has also considered the malfunction, primarily due to the malfunctions that affect the generation whether to allow a control for the ESC lack of a malfunction indicator lamp. of control or response signals in the to be disabled by the driver; however, The agency believes that such a warning vehicle’s electronic stability control heavy vehicles currently equipped with is important to ensure that the driver system is detected. Specifically, the ESC ESC systems do not include on/off could have the malfunction corrected at malfunction telltale will be required to

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be mounted in the driver’s compartment The agency believes that the symbol agency found that the ISO J.14 symbol in front of and in clear view of the used to identify ESC malfunction and close variations were the symbols driver and be identified by the symbol should be standardized with the symbol used by the greatest number of vehicle shown for ‘‘ESC Malfunction Telltale’’ used on light vehicles. The symbol manufacturers that used an ESC symbol or the specified words or abbreviations established in FMVSS No. 126 is the before the requirement was established. listed in Table 1 of FMVSS No. 101, International Organization for Furthermore, FMVSS No. 126 allows, as Controls and displays. FMVSS No. 101 Standardization (ISO) ESC symbol, an option, the use of the text ‘‘ESC’’ in includes a requirement for the telltale designated J.14 in ISO Standard 2575. place of the telltale symbol. This same symbol, or abbreviation, and the color The symbol shows the rear of a vehicle option is being proposed. required for the indicator lamp to show trailed by a pair of ‘‘S’’ shaped skid a malfunction in the ESC system. marks, shown below in Figure 5. The

The color of the ESC malfunction status of the ESC system during a which we could use to evaluate the roll telltale specified in Table 1 of FMVSS roadside safety inspection. stability performance and the yaw No. 101 for light vehicles equipped with Accordingly, this NPRM proposes that stability performance of truck tractors ESC is yellow, which is the color used the ESC malfunction telltale must be and large buses. Several of these to communicate to the driver the activated as a check of lamp function maneuvers were also tested by industry condition of a malfunctioning vehicle either when the ignition locking system and some of them are allowed for use system that does not require immediate is turned to the ‘‘On’’ (‘‘Run’’) position in testing for compliance to the UN ECE correction. The agency chose to when the engine is not running or when stability control regulation. The associate indication of an ESC system the ignition locking system is in a agency’s goal was to develop one or malfunction with a yellow telltale color position between the ‘‘On’’ (‘‘Run’’) and more maneuvers that showed the most as a warning to the driver because we ‘‘Start,’’ which is designated by the promise as repeatable and reproducible believe that it communicates the level of manufacturer as a check position. roll and yaw performance tests for which objective pass/fail criteria could urgency with which the driver must 3. ESC Activation Indicator seek to remedy the malfunction of the be developed. ESC system. The agency is requesting comment on As the research program progressed, whether there is a safety need for an the data indicated that the ramp steer For this proposed rule, we believe ESC activation indicator. In the light maneuver to evaluate roll stability that the ESC malfunction telltale and vehicle ESC rulemaking, the agency performance and the sine with dwell color designation developed for light considered the safety need for an ESC maneuver to evaluate yaw stability vehicles would be appropriate for use activation indicator to alert the driver performance were the most promising. on heavy vehicles. Accordingly, the during an emergency situation that the The slowly increasing steer maneuver agency proposes that the ESC ESC is activating. NHTSA conducted a was developed to normalize testing malfunction telltale symbol and color study using the National Advanced conditions for each vehicle so that the requirements of FMVSS No. 101 be Driving Simulator (NADS), which level of stringency for each test vehicle proposed for use on truck tractors and included experiments to gain insight would be similar. The agency also found buses, and that the abbreviation ‘‘ESC’’ into the various possibilities regarding that the SIS maneuver could also be should be allowed as an option instead ESC activation indicators. The study used to evaluate the engine torque of the symbol. compared the performance of 200 reduction capability of a vehicle’s ESC In addition to the ESC malfunction participants in driving maneuvers on a system, which is important because telltale being used to warn the driver of wet pavement, and used road departures engine torque reduction may bring a a malfunction in the ESC, the telltale is and eye glances to the instrument panel vehicle under control before brakes are also used as a check of lamp function as measures of driver performance. The applied. After further testing, the agency during vehicle start-up. We believe that significant finding was that the drivers was able to develop test parameters for the ESC malfunction telltale should be who received various ESC activation the SWD maneuver so that both roll activated as a check of lamp function indicators did not perform better than stability and the yaw stability could be either when the ignition locking system drivers who were given no indicator. evaluated using a single maneuver and is turned to the ‘‘On’’ (‘‘Run’’) position That finding formed the basis for the loading condition. This development whether or not the engine is running. agency’s decision not to require an ESC eliminated the need for the ramp steer This function provides drivers with the activation indicator for light vehicles. maneuver to evaluate roll stability information needed to ensure that the performance. ESC system is operational before the F. Performance Requirements and Therefore, based on testing at VRTC vehicle is driven. It also provides Compliance Testing and the results from industry-provided Federal and State inspectors with the The agency’s research initially test data, two stability proposed means to determine the operational focused on a variety of maneuvers performance tests have been chosen to

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evaluate ESC systems on truck tractors different suspension systems, and automatically attempts to reduce engine and large buses—the SIS test and the wheelbase and other dimensions, among torque. To confirm ESC activation, SWD test. other things. To normalize the severity engine torque output and driver The agency also considered the ECE of the SWD maneuver that follows, each requested torque data are collected from performance tests for heavy vehicle vehicle is tested based on its steering the vehicle’s J1939 communication data stability control systems, which are wheel angle determined in the SIS link and compared. During the initial included in the brake systems maneuver. The agency is proposing a stages of each maneuver, the rate of regulation, ECE Regulation 13. The 0.5g lateral acceleration target because change over time of engine torque performance test for a heavy vehicle our test results indicated that a truck output and driver requested torque will with a directional control function tractor or large bus is highly likely to be consistent. Upon ESC activation, the includes meeting the requirements in experience instability at that level of ESC system activation causes a one of eight tests allowed for lateral acceleration. Even though the commanded engine torque reduction, compliance. The eight tests are as vast majority of truck tractors are typical even though the driver requests follows: Reducing radius test (which is 6x4 tractors, there are other increased torque by attempting to identical to the decreasing radius test configurations, such as those with 2- accelerate the vehicle to maintain the discussed above), step steer input test, axle or 4-axle configurations and buses, required constant speed. Therefore, the sine with dwell, J-turn, mu-split lane which would require a different steering rate of change over time of engine change, double lane change, reversed wheel angle to normalize the test torque output and driver requested steering test or ‘‘fish hook’’ test, and conditions for each different vehicle. torque will diverge. asymmetrical one period sine steer or To perform the SIS maneuver, the For each of the six SIS test runs, the pulse steer input test. No test procedure tractor or bus is driven at a constant commanded engine torque and the or pass/fail criteria are included in ECE speed of 30 mph, and then the steering driver requested torque signals must Regulation 13, but it is left to the controller increases the steering wheel diverge at least 10 percent 1.5 seconds discretion of the Type Approval testing angle at a slow, continuous rate of 13.5 after the beginning of ESC system authority in agreement with the vehicle degrees per second. The steering wheel activation. This test demonstrates that manufacturer to show that the system is angle is increased linearly from zero to the ESC system has the capability to functional. 270 degrees and then held constant for reduce engine torque, as required in the The issue of whether the U.S. should one second, after which the maneuver functional definition. adopt the stability control requirements concludes. The vehicle is subjected to The metric used to measure the similar to those in ECE Regulation 13 is two series of runs, one using clockwise engine torque reduction performance is addressed in the context of whether a steering and the other using stated in terms of the difference in definitional requirement specifying counterclockwise steering, with three percent between the actual engine required equipment along with a tests performed for each test series. torque output and driver requested performance test that does not include During each test run, ESC system torque input just after ESC activation. a test procedure or pass/fail criteria activation must be confirmed. If ESC The pass-fail criterion that the agency would be considered sufficiently system activation does not occur during proposes for this test is that the stability objective for a safety standard. The the maneuver, then the commanded control system must be able to reduce agency considered several of the eight steering wheel angle is increased by engine torque output by a minimum of ECE tests that we believed showed the 270-degree increments up to the 10 percent from the torque output most promise for repeatability and vehicle’s maximum allowable steering requested by the driver, which will be reproducibility, and decided to focus on angle until ESC activation is confirmed. measured 1.5 seconds after the time the SWD test, which is one of the eight From the SIS tests, the value ‘‘A’’ is when the ESC activated. The vehicles tests allowed for compliance testing to determined. ‘‘A’’ is the steering wheel that the agency tested were all able to ECE Regulation 13. However, in light of angle, in degrees, that is estimated to meet this proposed performance level. the requirement in the Motor Vehicle produce a lateral acceleration of 0.5g for 2. Roll and Yaw Stability Test—SWD Safety Act that FMVSSs be stated in that vehicle. Using linear regression on objective terms, NHTSA is required to the lateral acceleration data recorded The objective of the sine with dwell develop objective performance criteria between 0.05g and 0.3g for each of the test is to subject a vehicle to a maneuver for the SWD test to be set forth in the six valid SIS tests, a linear extrapolation that will cause both roll and yaw regulatory text. is used to calculate a steering wheel instabilities and to verify that the ESC angle where the lateral acceleration system activates to mitigate those 1. Characterization Test—SIS would be 0.5g. If ESC system activation instabilities. The SWD test is based on The agency is proposing to conduct occurs prior to the vehicle experiencing a single cycle of a sinusoidal steering compliance testing characterization lateral acceleration of 0.3g, then the data input. For testing, we are proposing to using a slowly increasing steer to used during the linear regression will be use a frequency of 0.5 Hz (1⁄2 cycle per determine the steering wheel angle that data recorded between 0.05g and second or 1 cycle in 2 seconds) was needed to achieve 0.5g of lateral the lateral acceleration measured at the used with a pause or dwell of 1.0 acceleration at 30 mph and also to time of ESC system activation. The six second after completion of the third evaluate the capability of the ESC values derived from the linear quarter-cycle of the sinusoid. We chose system to reduce engine torque. The SIS regression are then averaged and a 0.5 Hz frequency because it produces maneuver has been used for many years rounded to the nearest 0.1 degree to the most consistently high severity on by the agency and the industry to produce the final quantity, ‘‘A,’’ used the majority of the vehicles tested by the determine the unique dynamic during the SWD maneuver. agency. Hence, the total time for the characteristics of a vehicle. This As part of the SIS characterization steering maneuver is three seconds. maneuver allows the agency to test, the engine torque reduction test is Conceptually, the steering profile of determine the relationship between the also conducted. As mentioned above, this maneuver is similar to that steering wheel angle and lateral during each of the six completed SIS expected to be used by real drivers acceleration for a vehicle, which varies maneuvers, ESC activation is confirmed during some crash avoidance due to different steering gear ratios, by verifying that the system maneuvers. As the agency found in the

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light vehicle ESC research program, the of test runs. One series uses vehicle speed, which results in a severity of the SWD maneuver makes it counterclockwise steering for the first reduction in the lateral acceleration, Ay, 2 a rigorous test while maintaining half-cycle, and the other series uses because Ay = V /R, where V is the steering rates within the capabilities of clockwise steering for the first half- vehicle speed, and R is the radius of human drivers. We believe that the cycle. The steering amplitude for the curvature of vehicle path. However, maneuver is severe enough to produce initial run of each series is 0.3A, where lateral acceleration was found to be less rollover or vehicle loss-of-control A is the steering wheel angle favorable than a ‘‘normalized’’ without a functioning ESC system on determined from the SIS maneuvers calculation, lateral acceleration ratio, the vehicle. discussed in section V.F.1 above. In developed from the vehicle’s lateral For a truck tractor, the SWD test each of the successive test runs, the acceleration measured during the would be conducted with the truck steering amplitude would be increased maneuver because the lateral tractor coupled to an unbraked control by increments of 0.1A until a steering acceleration alone does not account for trailer and loaded with ballast directly amplitude of 1.3A or 400 degrees, different stability thresholds among over the kingpin. The combination whichever is less, is achieved. Upon different vehicles. The agency believes vehicle would be loaded to 80 percent completion of the two series of test runs, that LAR has the most potential for an of the tractor’s GVWR. Testing indicates post-processing of the yaw rate and accurate measure of an ESC system to that this is sufficient load on the tractor lateral acceleration data to determine prevent rollovers. From the agency’s to enable the tractor’s stability control the lateral acceleration ratio, yaw rate testing, we have noted that LAR mass estimation program to provide full ratio, and lateral displacement, as differentiates vehicles equipped with tractor braking intervention during the discussed below. stability control systems as well as the SWD maneuver. The ballast is placed potential determine and quantify roll (a) Roll Stability Performance low on the trailer to minimize the instability. Lateral acceleration ratio is likelihood of actual trailer rollover, and The LAR is a performance metric calculated by dividing the vehicle’s the trailer is equipped with outriggers in developed to evaluate the ability of a lateral acceleration, corrected for roll case the ESC system does not function vehicle’s ESC system to prevent angle, at a specified time after the properly to prevent the trailer from rollovers. Lateral acceleration is completion of steer (COS) by the peak rolling over. measured on a bus or a tractor and corrected lateral acceleration For a bus, the vehicle is loaded with corrected for the vehicle’s roll angle. As experienced during the second half of a 68-kilogram (150-pound) water a performance metric, the corrected the sine maneuver (including the dwell dummy in each of the vehicle’s lateral acceleration value is normalized period). The LAR at two time intervals designated seating positions, which by dividing it by the maximum lateral after completion of steer is calculated to would bring the vehicle’s weight to less acceleration that was determined at any determine the change in lateral than its GVWR. No ballast is placed in time between 1.0 seconds after the acceleration from the peak lateral the cargo hold beneath the passenger beginning of steering and the acceleration. A reduction or decay in compartment so that the desired CG completion of steering. the lateral acceleration ratio at specified height of the test load can be attained. Conceptually, stability control system intervals after completion of steer is an The SWD test would be conducted at intervention will reduce lateral indication that the stability control a speed of 72 km/h (45 mph). An acceleration of the vehicle during a system has intervened to reduce the automated steering machine would be crash avoidance steering maneuver. likelihood of vehicle rollover. The used to initiate the steering maneuver. This intervention increases the roll lateral acceleration ratio, LAR, is Each vehicle is subjected to two series stability of the vehicle by reducing the determined as follows:

Where A_y Veh (COS + 0.75 sec, + 1.5 means the component of the vector the tractor during a test. One challenge sec,) is the corrected for roll lateral acceleration of a point in the vehicle with using wheel lift is that it does not acceleration value at the specified time perpendicular to the vehicle x axis necessarily indicate that rollover is after the completion of steer, and Max (longitudinal) and parallel to the road imminent. For example, certain vehicle Ay is the peak corrected lateral plane.’’ This definition was carried over, suspension designs are likely to cause acceleration measured during the effectively unchanged, to the more wheel lift during severe cornering second half of the sine maneuver recent revision of SAE’s Vehicle maneuvers, and also non-uniform test (including the dwell period), i.e., from Dynamics Terminology, SAE surfaces can cause brief instances of time 1.0 second after the beginning of J670_200801. The agency is proposing wheel lift. steer to the completion of steer. to use the same definition of lateral Therefore, the agency proposes In developing the performance acceleration for this standard as was evaluating vehicle roll stability requirements for light vehicle ESC used in FMVSS No. 126. performance by calculating the LAR at systems, several commenters requested The agency’s research also looked at 0.75 seconds and at 1.5 seconds after the that the agency include a definition for wheel lift measurement as a possible completion of steer. The two the term ‘‘lateral acceleration’’ and performance measure. Wheel lift is the performance criteria are described define a method for determining the most intuitive performance measure we below: lateral acceleration at the vehicle’s considered because wheel lift precedes • From data collected from each SWD center of gravity. In FMVSS No. 126, the all rollovers. Wheel lift is considered to maneuver executed, a vehicle equipped agency uses the definition from SAE be lift that is two inches or greater, with a stability control system must J670e, Vehicle Dynamics Terminology, which occurs for any wheel of the have a LAR of 30 percent or less 0.75 which states, ‘‘Lateral Acceleration vehicle, including the control trailer for seconds after completion of steer. This

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LAR will be calculated from the of the steering input, the lateral instability. The YRR expresses the vehicle’s lateral acceleration, corrected acceleration must not exceed 10 percent lateral stability criteria for the sine with for roll angle, at its center of gravity of the maximum lateral acceleration dwell test to measure how quickly the position. recorded during the steering maneuver. vehicle stops turning, or rotating about • From data collected from each SWD The agency believes that these criteria its vertical axis, after the steering wheel maneuver executed, a vehicle equipped represent an appropriate stability is returned to the straight-ahead with stability control must have a LAR threshold. NHTSA’s research indicates position. A vehicle that continues to of 10 percent or less at 1.5 seconds after that an ESC system’s ability to maintain turn or rotate about its vertical axis for completion of steer. This LAR will be an LAR above these criteria would an extended period after the steering calculated from the vehicle’s lateral provide an acceptable probability that wheel has been returned to a straight- acceleration, corrected for roll angle, at the vehicle would remain stable and ahead position is most likely its center of gravity position. that a level of LAR above these criteria experiencing oversteer, which is what The performance criteria mean that would result in a high probability of the ESC is designed to prevent. The lateral 0.75 seconds after the completion of the vehicle becoming unstable. stability criterion, expressed in terms of steering input, the corrected lateral YRR, is the percent of peak yaw rate that (b) Yaw Stability Performance acceleration must not exceed 30 percent is present at designated times after of the maximum lateral acceleration The yaw rate ratio is a performance completion of steer. recorded during the steering maneuver, metric used to evaluate the ability of a The yaw rate ratio, YRR, is and at 1.5 seconds after the completion vehicle’s ESC system to prevent yaw determined as follows:

Where YVehicle (COS + 0.75 sec, + 1.5 rate recorded. The agency believes that roll instability of the vehicle since the sec) is yaw rate value at a specified time these criteria represent an appropriate lateral acceleration would be reduced. after the completion of steer, and Max stability threshold. NHTSA’s research This is clearly, however, not a desirable YVehicle is the maximum yaw rate indicates that an ESC system’s ability to compromise. measured during the second half of the maintain an YRR above these criteria Because a vehicle that simply sine maneuver including the dwell would provide an acceptable probability responds poorly to steering commands period from time 1.0 second after the that the vehicle would remain stable may be able to meet the proposed beginning of steer until the completion and that a level of YRR above these stability criteria, a minimum of steer during each maneuver. criteria would result in a high responsiveness criterion is also This performance metric is identical probability of the vehicle becoming proposed for the SWD test. Using a to the metric used in the light vehicle unstable. lateral displacement metric to measure ESC system performance requirement in (c) Lateral Displacement responsiveness ensures that the vehicle FMVSS No. 126. We believe that this responds to an initial steering input to metric is equally applicable to truck Lateral displacement is a performance avoid an obstacle. This metric was tractors and large buses, though it is metric used to evaluate the chosen because it is objective, easy to calculated at different time intervals responsiveness of a vehicle, which measure, has good discriminatory after the completion of steer. relates to its ability to steer around capability, and has a direct relation to Therefore, the agency proposes to objects. Stability control intervention obstacle avoidance. evaluate yaw stability performance by has the potential to significantly The proposed lateral displacement calculating the YRR at 0.75 seconds and increase the stability of the vehicle in criterion is that a truck tractor equipped at 1.5 seconds after the completion of which it is installed. However, we with stability control must have a lateral steer. The two performance criteria are believe that these improvements in displacement of 7 feet or more at 1.5 described below: vehicle stability should not come at the • seconds from the beginning of steer, From data collected from each expense of poor lateral displacement in measured during the sine with dwell 45-mph SWD maneuver executed, a response to the driver’s steering input. maneuver. For a bus, the proposed vehicle equipped with a stability control A hypothetical way to pass a stability performance criterion is a lateral system must have a YRR of 40 percent control performance test would be to displacement of 5 feet or more at 1.5 or less 0.75 seconds after completion of make either the vehicle or its stability seconds after the beginning of steer. The steer. control system intervene simply by • lateral displacement criteria is less for a From data collected from each 45- making the vehicle poorly responsive to bus because a large bus has a longer mph SWD maneuver executed, a vehicle the speed and steering inputs required wheelbase than a truck tractor and equipped with stability control must by the test. An extreme example of this higher steering ratio, which makes it have a YRR of 15 percent or less at 1.5 potential lack of responsiveness would less responsive than a truck tractor. The seconds after completion of steer. occur if an ESC system locked both front value will be calculated from the double The performance criteria mean that wheels as the driver begins a severe integral with respect to time of the 0.75 seconds after the completion of the avoidance maneuver that might lead to measurement of the corrected for roll steering, the yaw rate must not exceed vehicle rollover. Front wheel lockup lateral acceleration at the vehicle center 40 percent of the peak yaw rate recorded would create an understeer condition in of gravity, as expressed by the formula: during the second half of the sine the vehicle, which would result in the Lateral Displacement = ∫∫Ay maneuver including the dwell period, vehicle plowing straight ahead and CG dt and at 1.5 seconds after the completion colliding with an object the driver was Where: AyCG is the corrected for roll of the steering input, the yaw rate must trying to avoid. It is very likely that lateral acceleration at the center of not exceed 15 percent of the peak yaw front wheel lockup would reduce the gravity height of the vehicle

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This is the same performance metric maneuver. Hence, a vehicle that avoids variations of the agency’s proposed used in FMVSS No. 126. Furthermore, loss of control according to our objective maneuver. the vehicle would be required pass this lateral acceleration and yaw rate decay We also recognize that, over time, requirement during the every execution definitions demonstrates that it has an manufacturers will be able to develop the SWD maneuver where the steering ESC system typical of today’s other methods for certifying compliance wheel angle is 0.7A or greater. technology and would have safety with the proposed standard. For benefits. example, manufacturers can develop 3. Alternative Test Maneuvers computer models or simulations to Considered In addition to our test results, the agency thoroughly evaluated the test demonstrate ESC system performance. We have considered other test vehicles and test data submitted by However, we recognize that these maneuvers besides the sine with dwell EMA and others to the agency. EMA alternative methods may not be suitable test. The SWD maneuver was tentatively provided information on one tractor that for atypical vehicles that are custom- selected over the other maneuvers appeared to satisfy the agency’s built for customers. We seek comment discussed above and below because our proposed SWD performance criteria on the issues surrounding research demonstrates that it has the without a stability control system. After manufacturers’ certification of most optimal set of characteristics, careful review of this data, we do not compliance including the assumptions including the severity of the test, believe this fact means the test has no made regarding manufacturers’ current repeatability and reproducibility of value.43 It is possible that there are and future test facilities, the methods results, and the ability to address currently truck tractors or large buses used by manufacturers to validate ESC rollover, lateral stability, and sold today that are exceptionally yaw system performance, the ability of responsiveness. stable, even in a severe maneuver such manufacturers to use other methods The agency’s research initially (such as computer modeling, focused on developing the ramp steer as a double lane change, which the SWD maneuver is designed to simulate. When simulation, or alternative test maneuver to evaluate the roll stability maneuvers) to certify compliance, the evaluating light vehicles, the agency performance and the sine with dwell cost of certification, and the issues noted that there was a very small maneuver to evaluate the yaw stability surrounding certification of atypical number of vehicles that were stable performance. However, after additional truck tractors. testing, we were able to develop test enough without a stability control Below, we discuss the alternative test parameters for the sine with dwell system to pass our performance criteria maneuvers that were considered and maneuver so that both roll stability and without an ESC system. Therefore, the what we considered to be acceptable yaw stability could be evaluated using existence of vehicles that could pass the performance criteria for each test. We a single loading condition and test proposed SWD test without a stability also discuss why we are choosing the maneuver. The sine with dwell control system simply indicates that it SWD maneuver for compliance testing maneuver has typically been used to would take many tests to cover all in lieu of each of these maneuvers. We evaluate only the yaw instability of a potential instability scenarios across invite comment on each of these test vehicle. The agency has previously used varying vehicle designs in order to maneuvers, including whether they a lightly loaded vehicle weight design a perfect test regime, as should be used instead of, or along with, condition for such evaluations where discussed earlier. Such a complex test the proposed compliance test the lightly loaded condition and the regime would require excessive costs to maneuvers. resulting lower CG height were much manufacturers to ensure compliance more likely to cause vehicle directional and excessive costs to the agency to (a) Characterization Maneuver loss-of-control as opposed to rollover. In determine and enforce compliance. While NHTSA has conducted the light vehicle ESC standard, the sine We recognize that manufacturers may extensive testing using the SIS with dwell maneuver is used to evaluate wish to base their certification of maneuver, we believe that alternative only yaw instability, not roll instability, compliance with this proposed standard methods may be used to determine the with the vehicle loaded to LLVW only on their vehicles’ performance in steering wheel angle needed to achieve but not to GVWR. Given the different NHTSA’s proposed test maneuvers. If 0.5g of lateral acceleration at 30 mph. dynamics of heavy vehicles when manufacturers intend to conduct the For example, a test based on the SAE compared to light vehicles, NHTSA maneuvers proposed by the agency, they J266 circle test may yield a similar evaluated several loading conditions may need to make additional steering wheel angle without requiring and found that a loading condition investments in their facilities or have the track space necessary to conduct the which equals 80 percent of the tractor’s their certification testing performed at a SIS maneuver. The steering wheel angle GVWR enables us to evaluate roll contractor’s facility. However, we that produces 0.5g of lateral acceleration instability as well as yaw instability. believe some manufacturers may have at 30 mph may be above the ESC The number of tests that would be already made these investments, and system’s activation threshold for some needed to cover all likely vehicle others would make similar investments vehicles, making it impractical to operational conditions for varying as they develop and validate ESC conduct a direct measurement of the vehicle designs is potentially large, and systems for their vehicles. This is based steering wheel angle. The agency seeks many tests (particularly those using low on our understanding of the maneuvers comment on the feasibility of an friction surfaces) may not be sufficiently used by the heavy-vehicle industry for alternative characterization test based repeatable for an objective performance ESC system development and upon the SAE J266 circle test. requirement. Our testing indicates that validation, some of which include the SWD maneuver is sufficiently severe (b) Roll Stability Test Maneuvers to ensure that nearly all vehicles 43 As discussed earlier, EMA’s testing of Vehicle To evaluate roll instability, we have without ESC would not be able to J used a control trailer with a wider track width and considered two alternative roll stability comply with the proposed performance a lower deck and used ballast that resulted in a test maneuvers—the J-turn and the ramp lower vehicle center of gravity than used by requirements. For example, the vehicles NHTSA’s researchers. Each of these differences steer maneuver. The two tests are we tested without ESC either had wheel caused EMA’s combination vehicle to be more similar in that both maneuvers require lift or spun out during the SWD stable than NHTSA’s during testing. the tested vehicle to be driven at a

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constant speed and then the vehicle is compliance tests in order to certify that exceptionally large steering wheel angle, turned in one direction for a certain their vehicles comply with NHTSA’s such as a bus with a long wheelbase the period of time. The test speed and the safety standards. We also recognize that, system may activate before the full severity of the turn are designed to over time, manufacturers are likely to steering wheel is input. cause a test vehicle to approach or use other methods such as simulation, Using a fixed-time steering input, we exceed its roll stability threshold such modeling, etc., to determine compliance would program the steering wheel that, without a stability control system, with Federal Motor Vehicle Safety controller to reach the desired steering the vehicle would exhibit signs of roll Standards. In this regard, we observe wheel angle in exactly 1.5 seconds using instability. Both tests would be that, because the J-turn and the ramp a constant steering rate, which was performed with the tractor loaded to its steer maneuvers are so similar, derived from the manually steered 150- GVWR. Furthermore, we would not manufacturers may be able to determine foot J-turn maneuver. Using this steering expect a vehicle that could pass one test compliance with a stability control method would prevent the RSM results to fail the other. standard by using the J-turn maneuver from varying with steering wheel angle The most notable difference between even if the agency ultimately decides to input. We are requesting comment as to the J-turn and the RSM maneuvers is use the RSM for compliance testing. whether fixed-rate steering or fixed-time that the J-turn is a path-following Thus, if a manufacturer sought to certify steering is a preferable manner for maneuver. That is, it is performed on a compliance based upon performance conducting the RSM. fixed path curve. In contrast, the RSM testing, a manufacturer would not The RSM would use a similar, but not maneuver is a non-path-following necessarily need to perform compliance identical lateral acceleration ratio maneuver that is performed with a fixed testing with an automated steering performance metric to evaluate roll steering wheel input. For example, controller. stability. As with the SWD maneuver, during the agency’s and EMA’s testing, In considering the RSM test the LAR used in the RSM would the J-turn maneuver was performed on conditions, the agency looked to its test indicate that the stability control system a 150-foot radius curve. In contrast, the data and the data submitted by EMA. is applying selective braking to lower RSM is performed based on a steering Data analysis indicated that the RSM lateral acceleration experienced during wheel angle derived from the SIS test. test performed from at an initial speed the steering maneuver. In the SWD We would expect that, with the RSM, of 30 mph is sufficient to demonstrate maneuver, the LAR is the ratio of the the radius of the curve would be close effective stability control performance lateral acceleration at a fixed point in to the fixed radius used in the J-turn for truck tractors. At GVWR, the tested time to the peak lateral acceleration maneuver. However, in the RSM, the buses were observed to have different during the period from one second after driver would not have to make speed thresholds at which wheel lift the beginning of steer to the completion adjustments and corrections to steering occurred and stability control initially of steer. In contrast, the LAR metric we to maintain the fixed path. activated. Without stability control, would use for the RSM would be the When comparing the J-turn to the buses were observed to produce wheel ratio of the lateral acceleration at a fixed RSM, the agency considers the RSM to lift between 35 and 39 mph in the RSM, point in time to the lateral acceleration be a preferable test maneuver because compared to tractors, which ranged at the end of ramp input, which is the the RSM maneuver can be performed from 28 to 30 mph. Large bus stability moment at which the steering wheel with an automated steering wheel control systems initially activated at angle reaches the target steering wheel controller. Because the J-turn is a path- speeds greater than 30 mph in the RSM, angle for the test. Also, in contrast to the following maneuver, a test driver must which was higher than the 26 mph SWD maneuver, the LAR measurements constantly make adjustments to the observed with tractors. In light of these for the RSM would be taken at a time steering input for the vehicle to remain differences, an initial speed of 36 mph when the steering wheel is still turned. in the lane throughout the test was selected for buses to ensure an This means that, although the SWD maneuver. Moreover, driver variability appropriate level of test severity and maneuver is a more dynamic steering could be introduced from test to test that stability control would intervene. maneuver, the LAR criteria for the RSM based upon minor variations in the Another issue in conducting the RSM would be greater than the LAR criteria timing of the initial steering input and is whether to use fixed rate steering or for the SWD maneuver. the position of the test vehicle in the to steer at a rate such that the full The performance criteria for the RSM lane. steering input is reached in a fixed time. would depend on whether fixed-rate In addition, the RSM appears to be Using fixed rate steering, the steering steering or fixed-time steering input is more consistent because it involves a wheel is turned a 175 degrees per used. For truck tractors and large buses fixed steering wheel angle rather than a second until the desired steering wheel using fixed-time steering input, we fixed path. There is negligible angle is reached. If a vehicle with a would expect that the LAR would be variability based on the timing of the lower steering wheel angle input, such less than 1.05 two seconds after the end initial steering input because the test is as a short wheelbase 4x2 tractor, is of ramp input and less than 0.8 three designed to begin at the initiation of tested using this steering method, the seconds after the end of ramp input. For steering input, rather than the vehicle’s desired steering wheel angle would be truck tractors tested using fixed-rate position on a track. Moreover, an reached relatively quickly after the steering inputs, we would expect that automated steering wheel controller can initial steering input. In contrast, for a the LAR would be less than 1.1 two more precisely maintain the required longer wheelbase truck or a large bus, seconds after the end of ramp input (the steering wheel input than a driver can. the desired steering wheel angle would point in time at which the target Therefore, we tentatively conclude that be reached relatively slowly after the steering wheel angle is reached) and less the RSM is more consistent and more initial steering input. This results in a than 0.9 three seconds after the end of repeatable than the J-turn, which is more severe test for vehicles with a ramp input. For buses using fixed-rate critical for agency compliance testing lower steering wheel angle because the steering, we would expect that the LAR purposes. predicted lateral acceleration of 0.5g would be less than 1.0 two seconds after Notwithstanding the above would be reached more quickly than for the end of ramp input and less than 0.7 observations, we recognize that many vehicles with a higher steering wheel three seconds after the end of ramp manufacturers perform NHTSA’s angle. In an extreme case with an input. The performance criteria for large

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buses would be lower because, as we was the SWD on dry pavement that is performance criterion, that during at stated above, when using fixed-rate similar to what is proposed in this least three of the four runs, the ESC steering input, the longer wheelbases of notice. The second maneuver was an system must provide a minimum level buses cause the maneuver to be less SWD maneuver conducted on wet (presently unspecified) of differential dynamic. Jennite. The third maneuver was a ramp braking. The agency has not had an In a March 2012 submission, which with dwell maneuver on wet Jennite.47 opportunity to conduct testing of this was revised with additional details in EMA did not provide any test data on maneuver, but we intend to do so to April 2012, EMA suggested that NHTSA the last two maneuvers. Thus, we determine whether this is a viable use different test speeds and considered them to be concepts rather alternative yaw stability test. performance criteria for the J-turn than fully developed maneuvers that we In light of the inability to develop a maneuver.44 EMA suggested that a test could consider using for yaw stability different performance-based yaw speed that is 30 percent greater than the testing. stability test, the agency is proposing to minimum speed at which the ESC We received no other alternative yaw use the SWD test maneuver to evaluate system intervenes with engine, engine performance tests from industry until yaw stability performance. Although we brake, or service brake control. Instead EMA’s submission of Vehicle J data in are proposing to use the SWD maneuver of measuring LAR, EMA suggested that, late 2010.48 EMA suggested using a wet for evaluating yaw stability, we request during three out of four runs, the Jennite drive through test maneuver comment on other yaw stability tests vehicle would be required to decelerate demonstrated yaw performance in a that could be suitable for performance at a minimum deceleration rate. NHTSA curve on a low friction surface. The testing and possible performance has conducted testing on variations of maneuver is based upon a maneuver the criteria for any such test. Furthermore, this EMA maneuver, and we plan to agency currently conducts on heavy we specifically request comment on all conduct further testing. We request vehicles to verify stability and control of aspects of EMA’s yaw stability test comments on EMA’s suggested test antilock braking systems while braking discussed in its March and April 2012 procedure and performance criteria for in a curve. As part of the test, a vehicle submissions, including the test the J-turn maneuver. is driven into a 500-foot radius curve conditions, test procedure, and possible Based on our testing to date, the with a low-friction wet Jennite surface performance criteria that would allow agency tentatively concludes that the at increasing speeds to determine the the agency to test both trucks and buses RSM is a preferable test to the J-run to maximum drive-through speed at which with this maneuver. demonstrate a stability control system’s the driver can keep the vehicle within ability to prevent roll instability. a 12-foot lane. As with the J-turn, we are (d) Lack of an Understeer Test However, as discussed in greater detail concerned about the repeatability of this The SWD maneuver is designed to below, in order to reduce the number of test maneuver because of variability in induce both roll and yaw responses compliance tests that the agency and the wet Jennite test surface and the from the vehicle being evaluated. those manufacturers who choose to driver’s difficulty in maintaining a However, the agency has no test to demonstrate compliance by conducting constant speed and steering input in the evaluate how the ESC responds when the agency’s performance tests must curve. understeer is induced. The technique perform, the agency proposes using on In a March 2012 submission, which used by a stability control system for test maneuver, the SWD, to demonstrate was revised with additional details in mitigating wheel lift, excessive oversteer both roll and yaw stability performance. April 2012, EMA provided information or understeer conditions is to apply Although we are proposing to use the about another yaw stability test along unbalanced wheel braking so as to SWD maneuver for evaluating roll with additional information on the J- generate moments (torques) to reduce stability, we request comment on issues turn maneuver.49 This maneuver would lateral acceleration and to correct related to the RSM and J-turn tests, simulate a single lane change on a wet excessive oversteer or understeer. including test conditions, steering input roadway surface. It would be conducted However, for a vehicle experiencing method, and performance criteria. within a 4 meter (12 foot) wide path. excessive understeer, if too much The roadway condition would be a wet, (c) Yaw Stability Test Maneuvers oversteering moment is generated, the low friction surface such as wet Jennite vehicle may oversteer and spin out with After evaluating several maneuvers on with a peak coefficient of friction of 0.5. obvious negative safety consequences. different surfaces, the agency was The other test conditions (i.e., road In addition, excessive understeer unable to develop any alterative conditions, burnish procedure, liftable mitigation acts like an anti-roll stability performance-based dynamic yaw test axle position, and initial brake control where it momentarily increases maneuvers that were repeatable enough temperatures) would be similar to those for compliance testing purposes. Bendix the lateral acceleration the vehicle can proposed in this NPRM. In this attain. Hence, too much understeer described two maneuvers intended to maneuver, the truck would enter the evaluate the yaw stability of tractors.45 mitigation can create safety problems in path at progressively higher speeds to the form of vehicle spin out or However, neither of these test establish the minimum speed at which 50 maneuvers was developed to a level that rollover. the ESC system intervenes and applies During the testing to develop FMVSS would make them suitable for the the tractor’s brakes. The maneuver No. 126, the agency concluded that agency to consider using as yaw would then be repeated four times at understanding both what understeer performance tests. that speed with the vehicle remaining In July 2009, EMA provided research mitigation can and cannot do is within the lane at all times during the complicated, and that there are certain information on several yaw stability test maneuver. EMA suggests, as a maneuvers.46 One of these maneuvers 50 EMA’s testing of Vehicle J on the 500-foot wet 47 This ramp with dwell maneuver is the same Jennite curve shows understeer mitigation at 44 Docket No. NHTSA–2010–0034–0032; Docket one identified by Bendix referenced in the prior maneuver entry speeds up to 34 mph, but at 35 No. NHTSA–2010–0034–0040. paragraph and in section IV.E.3. mph, the vehicle could not overcome understeer. 45 These tests are discussed in section IV.E.3. See 48 Docket No. NHTSA–2010–0034–0022; Docket See Docket No. NHTSA–2010–0034–0022; Docket Docket No. NHTSA–2010–0034–0037 and Docket No. NHTSA–2010–0034–0023. No. NHTSA–2010–0034–0023. At these low levels No. NHTSA–2010–0034–0038. 49 Docket No. NHTSA–2010–0034–0032; Docket of lateral acceleration, no adverse effects appeared 46 Docket No. NHTSA–2010–0034–0035. No. NHTSA–2010–0034–0040. to occur as a result of the understeer mitigation.

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situations where understeer mitigation vehicle operator. Malfunctions are test safely and to collect necessary could potentially produce safety generally simulated by disconnecting performance data. The compliance test disbenefits if not properly tuned. the power source to an ESC system program proposed in this NPRM would Therefore, the agency decided to enforce component or disconnecting an use essentially the same equipment and the requirements to meet the understeer electrical connection to or between ESC a subset of the instrumentation. As was criterion included in the ESC definition system components. Examples of done for FMVSS No. 126, the agency using a two-part process. First, the simulated malfunctions might include proposes including in the regulatory requirement to meet definitional criteria the electrical disconnection of the text the basic design parameters for the ensured that all had the hardware sensor measuring yaw rate, lateral automated steering machine, outriggers, needed to limit vehicle understeer. acceleration, steering wheel angle and the control trailer because this test Second, the agency required sensor, or wheel speed. When equipment and instrumentation can manufacturers to submit engineering simulating an ESC system malfunction, influence test vehicle performance. documentation at the request of the electrical connections for the telltale However, the proposed regulatory text NHTSA’s Office of Vehicle Safety lamp would not be disconnected. Also, does not include a list of the less critical Compliance to show that the system is because a vehicle may require a driving test instrumentation used during the capable of addressing vehicle phase to identify a malfunction, the compliance test. The agency’s common understeer. vehicle would be driven for at least two practice has been to provide Based on the agency’s experience minutes including at least one left and instrumentation details, test from the light vehicle ESC rulemaking one right turning maneuver. A similar instrumentation range, resolution, and and the lack of a suitable test to evaluate drive time exists in the FMVSS No. 126 accuracy for all the required understeer performance, the agency is test procedure. not proposing a test for understeer to After a malfunction has been instrumentation in the separate NHTSA evaluate ESC system performance for simulated and identified by the system, Laboratory Test Procedure. truck tractors and large buses. The the system is restored to normal Furthermore, the agency is aware that agency requests comment on this operation. The engine is started and the manufacturers and test facilities will be NPRM’s lack of a proposed understeer malfunction telltale is checked to ensure interested in knowing what instruments test. it has cleared. will be used for a compliance test program. The following table and 4. ESC Malfunction Test 5. Test Instrumentation and Equipment corresponding discussions identify the During execution of a compliance test For the truck tractor and large bus critical equipment and instrumentation the agency proposes simulating several stability control system research used by NHTSA’s researchers and for malfunctions to ensure the system and program, each test vehicle was fitted the most part, the same or similar is corresponding malfunction telltale with specific instrumentation and proposed for use by NHTSA’s Office of provides the required warning to the equipment necessary to execute each Vehicle Safety Compliance.

TABLE 3—CRITICAL TEST INSTRUMENTATION USED FOR DATA COLLECTION BY NHTSA RESEARCH

Vehicle test instrumentation Output/input Range Resolution Accuracy Make/model used

Programmable Steer- Controls Steering Max 40–60Nm (29.5– ...... Automotive Testing ing Machine with Wheel Angle Input. 44.3 lb-ft) torque at Inc. (ATI) Model: Steering Angle a hand wheel rate Spirit.3 Encoder. up to 1200 deg/sec. Handwheel Angle ...... ±800 deg ...... 0.25 deg ...... ±0.25 deg.

Multi-Axis Inertial Longitudinal, Lateral Accelerometers: ±2 g Accelerometers: ≤10 Accelerometers: Make: BEI Motion Sensing System. and Vertical Accel- ug. ≤0.05% of full Pak Model: MP–1. eration. range Roll, Yaw, and Pitch Angular rate sensors: Angular Rate Sen- Angular Rate Sen- Rate. ±100 deg/sec. sors: ≤0.004 deg/s. sors: 0.05% of full range.

Speed Sensor ...... Vehicle Speed to 0–201 km/h (0–125 .014 km/h (.009 mph) 0.1 km/h full scale ..... Make: RaceLogic DAS and Steering mph). Model: VBox. Machine.

Infrared Distance Left and Right Side 350–850 mm (14–35 0.3–8.0 mm (0.01–0.3 1% ...... Sensor Make: Measuring Sensor. Vehicle Height (For inches). inches). Wenglor. Model: calculated vehicle HT66MGV80. roll angle).

During research additional driver does not apply the brake during prevent vehicle rollover. During the instrumentation was used for collecting the maneuver, or the thermocouples program, the agency encountered many data outside the scope of the proposed used to monitor brake temperatures. instances of wheel lift and outrigger standard and that instrumentation is not (a) Outriggers contact with the ground indicating that discussed here. Furthermore, this table it was probable that rollover could occur does not include a discussion of non- Throughout the agency’s research during testing. Over many years of critical instrumentation like the brake program, truck tractors and buses were research of ESC systems, it has been pedal load cell used to ensure the test equipped with outrigger devices to proven that outriggers are essential to

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ensure driver safety and to prevent minimized. The width of the outrigger steering must follow an exact sinusoidal vehicle and property damage during assembly is 269 inches and the contact pattern over a three-second time period. NHTSA’s compliance testing. Although wheel to ground plane height is For the SWD maneuver, each test NHTSA conducted some of its testing adjustable to allow for various degrees vehicle is subjected to as many 22 with ESC systems disabled, thereby of body roll. A typical installation on a individual test runs all requiring increasing the need for outriggers, flatbed type trailer involves clamping activation at a specific vehicle speed, outriggers are still necessary as a safety and bolting the outrigger mounting each of which will require a different measure during testing of vehicles bracket to the main rails of the flatbed. peak steering wheel angle and equipped with an ESC system in case For buses, the outrigger installations corresponding steering wheel turning the system fails to activate. will not be as straightforward as the rate. To ensure the agency has an The agency proposes that outriggers outrigger installations on the control effective compliance program that will be used on all truck tractors and buses trailers, and we desire comments on bus not vary from one test laboratory to tested. Nevertheless, the agency outrigger design. This is because another, from one test driver to another, acknowledges, as it did during the outriggers cannot be mounted under the or from one test vehicle to another, each development of the light vehicle ESC flat structure, but instead must extend maneuver must be repeatable and system testing program, that outriggers through the bus. NHTSA used outriggers reproducible. The agency has extensive have the potential to influence the on the three large buses tested during its experience with execution of these and dynamics of a vehicle during research program and proposes using other steering maneuvers utilizing both performance testing. For light vehicles, outriggers for testing buses for human drivers and automated steering the agency determined that outrigger compliance with this rule. The agency controllers. Based upon this experience, influence could be noticeable. However, will use the same outrigger arms of the the agency has determined that a test we believe that outrigger influence on standard outrigger design that it plans to driver cannot consistently execute these heavy vehicles is minimal because of use for truck tractor testing. Therefore, kinds of dynamic maneuvers exactly as the higher vehicle weight and test load. the size, weight, and other design required repeatedly. We note that, for The agency has invested significant characteristics will be similar. the same reasons, the agency currently effort in outrigger designs that are both The location and manner of mounting requires that automated steering functional and minimize the impact to the outriggers on buses cannot be machines be used for execution of the the test vehicle dynamic performance. identical to truck tractors. Nonetheless, steering maneuvers performed under To reduce test variability and increase there are a limited number of large bus both the NCAP Rollover program and the repeatability of the test results, the manufacturers, which results in a the FMVSS No. 126 light vehicle ESC agency proposes to specify a standard limited number of unique chassis program. outrigger design for the outriggers that structural designs. Also, the agency will be used for compliance testing. The understands that large bus structural (c) Anti-Jackknife Cables agency used this same approach in designs do not change significantly from The agency proposes using anti- FMVSS No. 126 for compliance testing year-to-year. We believe that once jackknife cables when testing truck of light vehicle ESC systems. The outrigger mounts have been constructed tractors. Anti-jackknife cables would agency also made available the detailed for several different bus designs, those prevent the trailer from striking the design specifications by reference to a mountings can be modified and reused tractor during testing in the event that design document located in the agency during subsequent testing. The agency a jackknife event occurs during testing. public docket. has, in the document described above, This would prevent damage to the For truck tractors, the document provided additional engineering design tractor that may occur during testing. detailing the outrigger design to be used drawings and further installation We do not believe that the use of anti- in testing has been placed in a public guidelines for installing the standard jackknife cables would affect test docket.51 This document provides outrigger assemble to large buses. results, nor have we observed any detailed construction drawings, damage to test vehicles, including (b) Automated Steering Machine specifies materials to be used, and vehicle finishes, caused by anti- provides installation guidance. For As part of the heavy vehicle ESC jackknife cables. Nevertheless, we truck tractor combinations, the system research programs, the agency request comment on the necessity of the outriggers would be mounted on the performed testing that compared use of anti-jackknife cables during trailer. The outriggers are mounted mid- multiple runs with test-driver-generated agency compliance testing. way between the center of the kingpin steering inputs, and found that test and the center of the trailer axle (in the drivers cannot provide the same (d) Control Trailer fore and aft direction of travel), which repeatable results as those obtained with The agency proposes using a control is generally near the geometric center of an automated steering machine. trailer to evaluate the performance of a the trailer. They will be centered Therefore, this NPRM proposes that an tractor in its loaded condition. A control geometrically from side-to-side and automated steering machine be used for trailer would not be used when testing bolted up under the traditional flatbed the test maneuvers on the truck tractors buses. In FMVSS No. 121, the agency control trailer. Total weight of the and large buses in an effort to achieve specifies the use of an unbraked control outrigger assembly, excluding the highly repeatable and reproducible trailer for compliance testing purposes. mounting bracket and fasteners required compliance test results. An unbraked control trailer minimizes to mount the assembly to the flatbed An essential element of any the effect of the trailer’s brakes when trailer, is approximately 1,490 pounds. compliance test program is for the test testing the braking performance of a The bulk of the mass, over 800 pounds, being executed to be reproducible, a test tractor in its loaded condition. is for the mounting bracket which is that can be easily executed the same The agency has also considered using located under the trailer near the way by different testing facilities, and a braked control trailer in ESC vehicle’s lateral and longitudinal center repeatable, test results from repeated performance testing for truck tractors of gravity so that its inertial effects are tests of the same vehicle are identical. because the tractor-based stability The proposed 0.5 Hz SWD maneuver is control systems have the capability to 51 Docket No. NHTSA–2010–0034–0010. a complex test maneuver where the apply the trailer brakes during stability

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control intervention. This ability results using different control trailers. to monitor vehicle speed and data are provides a slightly greater vehicle First, the track width of the control provided as input to the automated retardation that could further help trailer is not specified. A trailer with a steering machine for maneuver prevent an impending rollover or reduce wider track width would be more stable activation. yaw instabilities. than a trailer with a narrower track Infrared height sensors would be used As described in section IV.C above, width, potentially affecting test results. to collect left and right side vertical ride the agency conducted numerous vehicle Second, the center of gravity of the height or displacement data for research test maneuvers using six control trailer is not specified in FMVSS calculating vehicle roll angle. One different trailers. For each trailer, a test No. 121. The center of gravity of the sensor would be mounted on each side series was conducted collecting data for trailer may be affected by the height of of the vehicle. With these data, roll each trailer in a braked and unbraked the load deck. A trailer with a higher angle is calculated during post- condition. The effects of stability load deck height would be less stable processing using trigonometry and control, trailer brakes, and trailer type than a trailer with a lower load deck would be used for correcting the were analyzed using a logistical height. Third, the center of gravity of the measured lateral acceleration data due regression model to predict if wheel lift load in FMVSS No. 121 testing is only to the effects caused by body roll. occurred during the test. A test was specified to be less than 24 inches above 6. Test Conditions conducted to determine the effects of the top of the tractor’s fifth wheel. trailer brakes when stability control However, a load with a lower center of (a) Ambient Conditions gravity (for example 12 inches) would systems were enabled. With stability The ambient temperature range be more stable than a load with a higher control systems enabled and trailer specified in other FMVSSs for outdoor center of gravity (for example 24 braking in the ‘‘off’’ position, the trailer brake performance testing is 0 °C to 38 was found not to be a significant factor inches). ° ° ° The performance measures specified C (32 F to 100 F). However, when the in predicting wheel lift. Hence, the agency proposed a range of 0 °C to 40 °C results indicate that the current FMVSS in this proposal were based upon ° ° NHTSA’s testing using the control (32 F to 104 F) for FMVSS No. 126, the No. 121 unbraked control trailer can be issue of tire performance at near used effectively in the stability control trailer used by VRTC researchers. Although the track width and center of freezing temperatures was raised. The system testing to determine the agency understood that near freezing capability of the tractor-based stability gravity of the trailer are not specified in the proposed regulatory text and the temperatures could impact the control system. variability of compliance test results. As NHTSA’s compliance tests must be center of gravity of the load is specified only by an upper bound, we request a result, the agency increased the lower objective, repeatable and reproducible. bound of the temperature range to 7 °C The goal of the testing program is to comment on possible specifications and ° appropriate levels of variability in (45 F) to minimize test variability at ensure that the ESC system takes the lower ambient temperatures. For the necessary actions of reducing engine trailer track width, trailer CG height, and load CG height for a control trailer same reasons, this NPRM proposes an torque and applying brakes to prevent ° to be used during ESC system testing. ambient temperature range of 7 C to yaw and roll instability. To achieve this 40 °C (45 °F to 104 °F) for testing. goal any trailer type could be used as (e) Sensors The agency proposes that the long as that trailer type becomes the A multi-axis inertial sensing system maximum wind speed for conducting ‘‘standard’’ trailer or ‘‘control trailer’’ would be used to measure longitudinal, the compliance testing for be no greater used for all tractor trailer testing. lateral, and vertical linear accelerations than 5 m/s (11 mph). This is the same Because it is the tractor performance and roll, pitch, and yaw angular rates. value specified for testing multi-purpose that is being evaluated, the use of a The position of the multi-axis inertial passenger vehicles (MPVs), buses, and standardized trailer will allow the test sensing system must be measured trucks under FMVSS No. 126. This is to distinguish the performance relative to the center of gravity of the also the same value used for compliance differences between different ESC tractor when loaded. To simplify testing for FMVSS No. 135, Light systems and tractor types. testing, the vertical center of gravity Vehicle Brake Systems. For FMVSS No. We believe that the current FMVSS location is assumed to be at the top of 126, the agency initially proposed a No. 121 unbraked control trailer can be the frame rails for tractors. For buses, maximum wind speed of 10 m/s (22 used effectively in the stability control the center of gravity height is assumed mph) for all vehicles. However, the testing to determine the capability of an to be at the height of the main interior agency decided to reduce the speed for ESC system. However, as discussed in floor of the bus. The measured lateral MPVs, buses, and trucks because of a section IV.D.5.(b) earlier, NHTSA’s acceleration and yaw rate data are concern that the higher wind speeds testing of EMA’s Vehicle J revealed that required for determining the lateral could impact the performance of certain the specifications for the control trailer displacement, LAR and YRR vehicle configurations (e.g., cube vans, in FMVSS No. 121 were not sufficient 52 performance criteria. All six of the 15 passenger vans, vehicles built in two to ensure test repeatability. sensing system signals are utilized in or more stages).53 Commenters to the There were three specifications, not the equations required to translate the proposed rule had estimated that a cross set forth in FMVSS No. 121, which motion of the vehicle at the measured wind of 22 mph could reduce lateral could affect test performance and location to that which occurred at the displacement by 0.5 feet, compared to prevent repeatable, consistent test actual center of gravity to remove roll, the same test conducted under calm pitch, and yaw effects. conditions. The agency agreed that wind 52 The FMVSS No. 121 control trailer specifications, set forth in S6.1.10.2 and S6.1.10.3 The vehicle speed would be measured speed could have some impact on the of FMVSS No. 121 provide that the center of gravity with a non-contact GPS-based speed lateral displacement for certain vehicle of the ballast on the loaded control trailer be less sensor. Accurate speed data is required configurations and believes that the than 24 inches above the top of the tractor’s fifth to ensure that the SWD maneuver is same argument is applicable testing wheel and that the trailer have a single axle with executed at the required 72.4 ± 1.6 km/ truck tractors and large buses. a GAWR of 18,000 pounds and a length, measured ± from the transverse centerline of the axle to the h (45.0 1.0 mph) test speed. Sensor centerline of the kingpin, of 258 ± 6 inches. outputs are available to allow the driver 53 See 72 FR 17286 (Apr. 6, 2007).

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Nevertheless, the agency notes that For testing large buses, the agency these systems require a period of initial specifying such a low maximum wind proposes loading the vehicle to a driving. speed can impose additional burdens on simulated multi-passenger The agency proposes to include a testing by restricting the environmental configuration. For this configuration the mass estimation drive cycle as a part of conditions under which testing can be bus is loaded with the fuel tanks filled pre-test conditioning. To complete this conducted. to at least 75 percent capacity, test drive cycle the test vehicle is driver, test instrumentation, outriggers accelerated to a speed of 64 km/h (40 (b) Road Test Surface and simulated occupants in each of the mph), and then, by applying the vehicle The SWD maneuver executed on a vehicle’s designated seating positions. brakes, decelerated at 0.3g to 0.4g to a high friction surface is a dynamically The simulated occupant loads are stop. challenging maneuver that evaluates the obtained by securing a 68 kilogram (150 (f) Brake Conditioning effectiveness of an ESC system. Low pound) water dummy in each of the test friction surfaces, such as wet Jennite, vehicle’s designated seating positions Heavy vehicle brake performance is are well known for producing a high without exceeding the vehicle’s GVWR affected by the original conditioning degree of braking and handling tests and GAWR. The 68 kilogram (150 and temperatures of the brakes. We variability compared to similar tests on pound) occupant load was chosen believe that incompletely burnished high friction surfaces. The variability is because that is the occupant weight brakes and excessive brake temperatures exacerbated by the difficulty in ensuring specified for use by the agency for can have an effect on ESC system test a consistent water depth across the test evaluating a vehicle’s load carrying results, particularly in the rollover surface. Therefore, this NPRM proposes capability under FMVSS Nos. 110 and performance testing, because a hard conducting the SWD test on a dry test 120. During loading, if any rating is brake application may be needed for the surface with a PFC of 0.9, which is exceeded the ballast load would be foundation brakes to reduce speed to typical of a dry asphalt surface or a dry reduced until the respective rating or prevent rollover. FMVSS No. 126 uses a simple concrete surface. As in other standards ratings are no longer exceeded. conditioning procedure by executing ten where the PFC is specified, we propose (d) Tires stops from 35 mph followed by three that the PFC be measured using an We propose testing the vehicles with stops at 45 mph. Subsequently, a cool ASTM E1136 standard reference test tire the tires installed on the vehicle at time down period of between 90 seconds and in accordance with ASTM Method of initial vehicle sale. The agency’s 5 minutes is required between each E1337–90, at a speed of 64.4 km/h (40 compliance test programs generally SWD maneuver allowing sufficient time mph), without water delivery. We are evaluate new vehicles with new tires. for the brakes to cool down but not so proposing incorporating these ASTM Therefore, we are proposing as a general long that the brakes lose all their provisions into the Standard. rule that a new test vehicle have less retained heat. However, for heavy (c) Vehicle Test Weight than 500 miles on the odometer when vehicles, brake conditioning and received for testing. operating temperatures are more critical The agency proposes that the For testing, the agency proposes that to brake performance than for light combined weight of the truck tractor tires be inflated to the vehicle vehicles primarily because the vast and control trailer be equal to 80 manufacturer’s recommended cold tire majority of heavy vehicles use drum percent of the tractor’s GVWR. To inflation pressure(s) specified on the brakes, which require more achieve this load condition the tractor is vehicle’s certification label or the tire conditioning than disc brakes. We loaded with the fuel tanks filled to at inflation pressure label. No tire changes believe that conditioning needs to be least 75 percent capacity, test driver, would occur during testing unless test more extensive and a brake temperature test instrumentation and ballasted vehicle tires are damaged before or range is preferable to a specified cool- control trailer with outriggers. Center of during testing. We are not proposing down period because each vehicle may gravity of all ballast on the control using inner tubes for testing because we have different cooling rates based on its trailer is proposed to be located directly have not seen any tire debeading in any configuration. above the kingpin. When possible, load test. The agency is proposing that the distribution on non-steer axles is in Before executing any SIS and SWD brakes be burnished before any testing proportion to the tractor’s respective maneuvers, the agency is proposing to is executed. We believe that the burnish axle GAWRs. Load distribution may be condition tires to wear away mold sheen procedure specified in S6.1.8 of FMVSS adjusted by altering fifth wheel position, and achieve operating temperatures. To No. 121, Air Brake Systems, provides if adjustable. In the case where the begin the conditioning the test vehicle the brake conditioning needed for the tractor fifth wheel cannot be adjusted so would be driven around a circle 46 stability control system testing. The as to avoid exceeding a GAWR, ballast meters (150 feet) in radius at a speed burnish procedure is performed by is reduced so that axle load equals that produces a lateral acceleration of conducting 500 brake snubs 54 between specified GAWR, maintaining load approximately 0.1g for two clockwise 40 mph and 20 mph at a deceleration of proportioning as close as possible to laps followed by two counterclockwise 10 fp 2. If the vehicle has already specified proportioning. laps. completed testing to FMVSS No. 121, The agency is proposing that liftable (e) Mass Estimation Drive Cycle we are not proposing to require the axles be in the down position for procedure be repeated. Instead, the testing. This is because we are Both truck tractors and large buses brakes would be conditioned for the conducting our proposed performance experience large changes in payload ESC with 40 snubs. The agency test in a loaded condition. Typically, in mass, which affects a vehicle’s roll and proposes that the brake temperatures be real world use, we believe that a truck yaw stability thresholds. To adjust the in the range of 65 °C to 204 °C (150 °F tractor loaded to 80% of its GVWR activation thresholds for these changes, to 400 °F) at the beginning of each test would operate with the liftable axle in stability control systems estimate the maneuver. We also propose that the the down position. Consequently, we mass of the vehicle after ignition cycles, propose to conduct compliance testing periods of static idling, and other 54 A snub is a brake application where the vehicle in that configuration. driving scenarios. To estimate the mass, is not braked to a stop but to a lower speed.

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brake temperature be measured by plug- of 3 Hz. Zero the filtered data to remove 5 degrees (when the initial steering type thermocouples installed on all sensor offset utilizing static pretest data. input is counterclockwise) or plus 5 brakes and that the hottest brake be used 3. Filter raw lateral, longitudinal and degrees (when the initial steering input for determining whether cool-down vertical acceleration data with a 12-pole is clockwise) after the end of the zeroing periods are required. phaseless Butterworth filter and a cutoff range is identified. The time identified After the brakes are burnished, frequency of 3 Hz. Zero the filtered data is taken to be the beginning of steer. immediately prior to executing any SIS to remove sensor offset utilizing static The agency understands that an or SWD maneuvers, the agency would pretest data. unambiguous reference point to define perform 40 brake application snubs 4. Filter raw speed data with a 12-pole the start of steering is necessary in order from a speed of 64 km/h (40 mph), with phaseless Butterworth filter and a cutoff to ensure consistency when computing a target deceleration of approximately frequency of 2 Hz. the performance metrics measured 0.3g. At end of the 40 snubs, the hottest 5. Filter left side and right side ride during compliance testing. The practical brake temperature would be confirmed height data with a 0.1-second running problem is that typical ‘‘noise’’ in the within the temperature range of 65 °C to average filter. Zero the filtered data to steering measurement channel causes 204 °C (150 °F to 400 °F). If the hottest remove sensor offset utilizing static continual small fluctuations of the brake temperature is above 204 °C (400 pretest data. signal about the zero point, so departure 6. The J1939 torque data collected as °F) a cool-down period would be from zero with very small steering a digital signal does not get filtered. provided until the hottest brake angles does not reliably indicate that the J1939 torque data collected as an analog temperature is measured within that steering machine has started the test signal is to be filtered with a 0.1-second range. If the hottest brake temperature is maneuver. NHTSA’s extensive running average filter. below 65 °C (150 °F) individual brake evaluation of zeroing range criteria has There are several events in the confirmed that the method successfully stops would be repeated to increase any calculation of performance metrics that one brake temperature to within the and robustly distinguishes the initiation require determining the time and/or of the SWD steering inputs from the target temperature range before the level of an event, including: Beginning compliance testing can be continued. inherent noise present in the steering of steer, 1.5 seconds after beginning of wheel angle data channel. The value for 7. Data Filtering and Post Processing steer, completion of steer, 0.75 second time at the beginning of steer used for after completion of steer, and 1.50 calculating the lateral displacement To determine if a test vehicle meets seconds after completion of steer. The the performance requirements of the metric is interpolated. agency proposes using interpolation 55 The completion of steer is a critical proposed standard, data needs to be for all of these circumstances because moment during the maneuver because measured and processed and ultimately interpolation provides more consistent the LAR and YRR metrics are used to calculate the lateral results than other approaches, such as determined at specific time intervals displacement, lateral acceleration ratio choosing the sample that is closest in after the completion of steer. The agency and yaw rate ratio performance time to the desired event. believes that an unambiguous point to measures. The agency understands that The beginning of steer is a critical define the completion of steer is also filtering and post processing methods, if moment during the maneuver because necessary for consistency in computing not defined, can have a significant the lateral displacement performance the required performance metrics during impact on the final test results used for measure is determined at exactly 1.5 compliance testing. The agency determining vehicle compliance. When seconds after the beginning of steer. For proposes considering the first developing FMVSS No. 126 the agency compliance purposes it is essential that occurrence of the ‘‘zeroed’’ steering received several comments the beginning of steer be determined wheel angle crossing zero degrees after recommending that filtering and accurately and consistently during each the second peak of steering wheel angle processing methods be defined and maneuver and each test. The process during the sine maneuver to be the included in the regulatory text. The proposed in this NPRM to identify the completion of steer. Although signal agency decided to add to the test beginning of steer uses three steps. The noise results in continual zero crossings procedures section of the final rule’s first step identifies when the steering as long the data is being sampled, the regulatory text a section that specified wheel velocity exceeds 40 degrees per first zero crossing after the steering the critical test filtering protocols and second. From this point, steering wheel wheel has begun to return to the zero techniques to be used for test data velocity must remain greater than 40 position is a logical end to the steering processing. We propose to include the degrees per second for at least 200 ms. maneuver. same information in this standard. In If the condition is not met, the next time Given the potential for the addition, the agency proposes to make steering wheel velocity exceeds 40 accelerometers used in the measurement available on NHTSA’s Web site the degrees per second is identified and the and determination of lateral acceleration actual MATLAB code used for post- 200 ms validity check is applied. This and lateral displacement to drift over processing the critical lateral iterative process continues until the time, the agency uses the data one acceleration, yaw rate and lateral conditions are satisfied. In the second second before the start of steering to displacement performance data. step, a zeroing range defined as the 1.0 ‘‘zero’’ the accelerometers and roll During post-processing the following second time period prior to the instant signal. Prior to the test maneuver, the data signals will be filtered and the steering wheel velocity exceeds 40 driver must orient the vehicle to the conditioned as follows: degrees per second. In the third step, the desired heading, position the steering 1. Filter raw steering wheel angle data first instance the filtered and zeroed wheel angle to zero, and be coasting with a 12-pole phaseless Butterworth steering wheel angle data reaches minus down (i.e., not using throttle inputs) to filter and a cutoff frequency of 10 Hz. the target test speed of 45 mph. This Zero the filtered data to remove sensor 55 Interpolation is a way of computing data values process, known as achieving a ‘‘quasi offset utilizing static pretest data. at the exact time that any of these events occur, steady-state,’’ typically occurs a few even though the digital samples did not coincide 2. Filter raw yaw, pitch and roll rate with the exact event point. Rather, one sample is seconds prior to initiation of the data with a 12-pole phaseless collected slightly before the time of the event and maneuver, but can be influenced by Butterworth filter and a cutoff frequency a second sample slightly after the time of the event. external factors such as test track traffic,

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differences in vehicle deceleration rates, If the sensors used to measure the about 5 percent of annual truck tractor etc. Any zeroing performed on test data vehicle responses are of sufficient sales, may need additional lead time to must be performed after a quasi-steady- accuracy, and have been installed and develop, test and equip these vehicles state condition has been satisfied, but configured correctly, use of the analysis with a stability control system. before the maneuver is initiated. The routines provided by NHTSA are Therefore, we are proposing to require proposed zeroing duration of one expected to minimize the potential for that severe service tractors and other second provides an adequate performance discrepancies among atypical tractors be equipped with ESC combination of sufficient time (i.e., NHTSA and industry test efforts. The systems beginning four years after the enough data is present so as to facilitate equations utilized are the same final rule is published. We note that we accurate zeroing of the test data) and equations used by the agency for its made a similar distinction between performability (i.e., the duration is not NCAP rollover program and the FMVSS typical 6x4 tractors and other tractors in so long that it imposes an unreasonable No. 126 light vehicle ESC program, and specifying the lead time for burden on the driver). were derived from equations of general amendments to FMVSS No. 121 The lateral acceleration data are relative acceleration for a translating mandating improved stopping distance collected from an accelerometer, reference frame utilizing the SAE performance.56 corrected for roll angle effects, and convention for Vehicle Dynamics However, in our stopping distance resolved to the vehicle’s CG using Coordinate Systems. rulemaking, we allowed extra time for coordinate transformation equations. Furthermore, NHTSA does not two-axle tractors to comply because The use of accelerometers is propose using inertially stabilized shorter wheelbase tractors (i.e., two-axle commonplace in the vehicle testing accelerometers for this test procedure. tractors) showed a risk of instability community, and installation is simple Therefore, lateral acceleration must be resulting from the improved stopping and well understood. However, in most corrected for vehicle roll angle during distance requirements. However, the cases, it is not possible to install a data post processing. Non-contact increased risk of instability in shorter lateral acceleration sensor at the displacement sensors are used to collect wheelbase vehicles led us to the location of the vehicle’s exact center of left and right side vertical opposite tentative conclusion in this gravity. For this reason, it is important displacements for the purpose of rulemaking. Because two-axle tractors to provide a coordinate transformation calculating vehicle roll angle. One have a particular risk of instability, we to resolve the measured lateral sensor is mounted on each side of the do not believe extending lead time for acceleration values to the vehicle’s vehicle, and is positioned at the two-axle tractors is warranted. center of gravity location. The specific longitudinal CG. With these data, roll The vast majority of new truck equations proposed to perform this angle is calculated during post- tractors are three-axle (6x4) vehicles, operation, as well as those used to processing using trigonometry as which facilitates standardization of ESC follows: for these vehicles. The available test correct lateral acceleration data for the ¥ effect of chassis roll angle, will be Equation 4: ayc = aymcos F azmsin F data for typical three-axle (6x4) tractors incorporated into the laboratory test Where: with stability control systems show that procedure and are included in the ayc is the corrected lateral acceleration (i.e., the existing ESC technology should MATLAB post processing routines used the vehicle’s lateral acceleration in a enable these vehicles to readily comply by the agency. plane horizontal to the test surface) with stability control requirements aym is the measured lateral acceleration in the proposed by the agency. In addition, the The equations used for coordinate vehicle reference frame agency’s benefit analysis indicates that transformation and vehicle body roll are azm is the measured vertical acceleration in as follows: the vehicle reference frame ESC provides substantial safety benefits to truck tractors. Hence, we believe that Equation 1: x″ = x″ ¥(Q′ 2 + Y′ F is the vehicle’s roll angle corrected accel it is important that the implementation 2)x + (Q′F′¥Y″)y + (Y ′F′ + Note: The z-axis sign convention is disp disp date for ESC on these vehicles be as Q″)z positive in the downward direction for both disp early as practicable so that these safety Equation 2: y″ = y″ + (Q′F′ + the vehicle and test surface reference frames. corrected accel benefits could be achieved. Y ″)x ¥(F′ 2 + Y ′ 2)y + (Y disp disp G. Compliance Dates and Several manufacturers of Class 8 ′Q′¥F″)z disp Implementation Schedule buses are already offering ESC as Equation 3: z″corrected = z″accel + (Y ′ ′¥ ″ ′ ′ ″ ¥ ′ The agency proposes that all new standard equipment on their vehicles F Q )xdisp + (Y Q + F )ydisp (F but we are not aware of any Class 7 bus 2 2 + Q′ )zdisp typical 6x4 truck tractors and all buses covered by this proposal would be that is available with ESC. We believe Where: that the manufacturers of Class 7 buses ″ ″ ″ required to meet this proposed standard x corrected, y corrected, and z corrected = effective two years after the final rule is would need some lead time to have the longitudinal, lateral, and vertical published. The current annual ESC systems developed, tested and accelerations, respectively, at the installed on their vehicles. Hence, for vehicle’s center of gravity installation rate for stability control ″ ″ ″ systems on new truck tractors is large buses, the agency proposes an x accel, y accel, and z accel = longitudinal, effective date of two years after the final lateral, and vertical accelerations, approximately 18 percent. Because there rule is published, primarily to respectively, at the accelerometer are currently only two suppliers of truck location tractor and large bus stability control accommodate manufacturers of Class 7 buses. xdisp, ydisp, and zdisp = longitudinal, lateral, systems, Bendix and Meritor WABCO, and vertical displacements, respectively, we believe that the industry will need VI. Benefits and Costs of the center of gravity with respect to lead time to ensure that the necessary the accelerometer location A. System Effectiveness F′ and F″ = roll rate and roll acceleration, production stability control systems are respectively available to manufacturers. As discussed above, direct data that Q′ and Q″ = pitch rate and pitch acceleration, For severe service tractors and tractors would show the effectiveness of respectively with four axles or more, the agency stability control systems is not available Y ′ and Y ″ = yaw rate and yaw acceleration, believes that manufacturers of these respectively atypical truck tractors, which represent 56 See 49 CFR 571.121, Table IIA.

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because stability control system for truck tractors, two modifications The results of UMTRI’s study and the technology on heavy vehicles is so new. were necessary. First, the UMTRI study agency’s revised effectiveness estimates Accordingly, NHTSA sponsored a based its effectiveness estimates on a were published in a January 2011 research program with Meritor WABCO simple aggregation of cases rather than research note entitled ‘‘Effectiveness of and UMTRI to examine the potential weighting the likelihood of occurrence Stability Control Systems For Truck effectiveness of stability control systems of each case. Second, based on NHTSA’s Tractors’’ (DOT HS 811 437).57 The on the fleet of truck tractors. A copy of independent review of the 159 cases, effectiveness estimates from that UMTRI’s report has been placed in the two cases were incorrectly categorized research note are summarized in the docket. as loss of control rather than untripped following table. However, for NHTSA to calculate the rollover and the effectiveness rating of effectiveness of stability control systems six cases were revised downward.

TABLE 4—EFFECTIVENESS RATES FOR ESC AND RSC BY TARGET CRASHES [Current NHTSA estimates]

Overall Untripped rollover Loss of control Technology effectiveness effectiveness effectiveness (%) (%) (%)

ESC ...... 28–36 40–56 14 RSC ...... 21–30 37–53 3

For large buses, it was not feasible to B. Target Crash Population system. For this analysis, particularly in conduct a similar statistical analysis multi-vehicle crashes, the subject because of limited crash data. However, The initial target crash population for vehicle is the at-fault or striking vehicle. NHTSA’s testing revealed that an estimating benefits includes all crashes The initial target crash populations were identical set of test maneuvers could be resulting in occupant fatalities, MAIS 1 retrieved from the 2006–2008 Fatality used to evaluate truck tractor and large and above nonfatal injuries, and Analysis Reporting System (FARS) and bus systems’ ability to prevent rollover property damage only crashes that were General Estimate System (GES). The and loss-of-control crashes. Therefore, the result of either (a) first-event FARS data were used for evaluating for the purpose of this proposal, the untripped rollover crashes and (b) loss- fatal crashes and the GES data were effectiveness of ESC and RSC systems of-control crashes (e.g., jackknife, cargo used for evaluating nonfatal crashes. shift, avoiding, swerving) that involved on large buses was assumed to be The injury data were converted to MAIS truck tractors or large buses and might identical to the performance of systems format and the following number of be prevented if the subject vehicle were crashes, fatalities, injuries, and deaths on truck tractors. equipped with a stability control were estimated.

TABLE 5—INITIAL TARGET CRASHES, MAIS INJURIES, AND PROPERTY DAMAGE ONLY VEHICLE CRASHES BY CRASH TYPE

MAIS 1–5 Crash type Crashes Fatalities Injuries PDOVs

Rollover ...... 5,510 111 2,217 3,297 Loss of control ...... 4,803 216 1,141 3,935

Total ...... 10,313 327 3,358 7,332 Source: 2006–2008 FARS, 2006–2008 GES. PDOVs: property damage only vehicles.

The 2006–2008 crash data were then would be equipped with RSC systems upon manufacturer production adjusted to take account of ESC and RSC (Base 2 population). The Base 1 estimates, about 26.2 percent of truck system installation rates in 2006–2008 population would benefit fully from this tractors manufactured in model year and in model year 2012. To determine proposal. However, the Base 2 2012 would be equipped with ESC the number of crashes that could be population would benefit only from the systems and 16.0 percent would be prevented by requiring that ESC systems incremental increased effectiveness of equipped with RSC systems. Adjusting be installed on new truck tractors, the ESC systems over RSC systems. the initial target crash populations using agency had to consider two subsets of Based upon data obtained from these estimates, the agency was able to industry, the agency estimates that the total crash population—those estimate the Base 1 and Base 2 about 1.9 percent of truck tractors in the vehicles that would not be equipped populations and the projected target on-road fleet in 2008 were equipped with stability control systems (Base 1 with ESC systems and 3.3 percent were crash population (Base 1 + Base 2) population) and those vehicles that equipped with RSC systems. Based expressed in the following table.

57 Docket No. NHTSA–2010–0034–0043.

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TABLE 6—PROJECTED CRASHES, MAIS INJURIES, AND PROPERTY DAMAGE ONLY VEHICLE CRASHES BY CRASH TYPE, CRASH SEVERITY, INJURY SEVERITY, AND VEHICLE TYPE FOR 2012 LEVEL

MAIS 1–5 Crash type Crashes Fatalities Injuries PDOVs

Base 1

Rollover ...... 3,263 66 1,313 1,952 Loss of Control ...... 2,786 125 662 2,283

Total ...... 6,049 191 1,975 4,235

Base 2

Rollover ...... 903 18 364 540 Loss of Control ...... 771 35 183 632

Total ...... 1,674 53 547 1,172

Base 1 + Base 2 (Projected Target Population)

Rollover ...... 4,166 84 1,677 2,492 Loss of Control ...... 3,557 160 845 2,915

Total ...... 7,723 244 2,522 5,407 Source: 2006–2008 FARS, 2006–2008 GES. PDOVs: property damage only vehicles.

The agency has also examined the benefits include both injury and non- rollover crashes that were used for the same crash data sources for large buses. injury components. The injury benefits analysis. In contrast, at the publication, Based upon this examination, the are the estimated fatalities and injuries there is only one effectiveness estimate agency estimates that an average of one that would be mitigated or eliminated for addressing loss-of-control crashes. target bus rollover and one target bus by ESC. The non-injury benefits include The benefits of this proposal were loss-of-control crash occurs per year that the travel delay and property damage derived by multiplying the projected would be affected by this proposal. savings from crashes that were avoided target population by the corresponding C. Benefits Estimate by ESC. Savings from reducing effectiveness rates. As shown in Table 7, property-damage-only vehicle crashes ESC systems are crash avoidance this proposal would prevent 1,807 to countermeasures that would mitigate also were included in the non-injury 2,329 target crashes, 49 to 60 fatalities, and even prevent crashes. Preventing a benefits. and 649 to 858 MAIS 1–5 injuries. crash not only would save lives and The benefits estimates for rollover Furthermore, the proposal would reduce injuries, it also would alleviate crashes are presented in a range in this eliminate 1,187 to 1,499 property- crash-related travel delays and property analysis. This is the result of a range of damage-only crashes. Table 7 presents damage. Therefore, the estimated ESC effectiveness figures in addressing the benefits by target crash type.

TABLE 7—ESTIMATED BENEFITS OF THE PROPOSAL

MAIS 1–5 Crash type Crashes Fatalities Injuries PDOVs

Base 1 Benefits

Rollover ...... 1,305–1,827 26–37 526–735 781–1,093 Loss of Control ...... 390 18 93 320

Total ...... 1,695–2,217 44–55 619–828 1,101–1,413

Base 2 Benefits

Rollover ...... 27 1 11 16 Loss of Control ...... 85 4 19 70

Total ...... 112 5 30 86

Benefits of the Proposal (Base 1 + Base 2)

Rollover ...... 1,332–1,854 27–38 537–746 797–1,109 Loss of Control ...... 475 22 112 390

Total ...... 1,807–2,329 49–60 649–858 1,187–1,499 Source: 2006–2008 FARS, 2006–2008 GES. PDOVs: property damage only vehicles.

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The non-injury benefits also include by determining the unit cost of property proposal would save (undiscounted) savings from the elimination of crash- damage and travel delay for each level $17.1 to $22.0 million from travel delays related travel delay and vehicle property of crash severity (e.g., fatal, MAIS 1–5, and property damage as a result of damage. Table 8 shows the total travel or property damage only) and crashes that would be prevented by this delay and property damage savings from multiplying that cost by the number of proposal. this proposal, broken down by target incidents of each type of crash crash type. These benefits were derived prevented. As shown in Table 8, this

TABLE 8—TOTAL TRAVEL DELAY AND PROPERTY DAMAGE SAVINGS [Undiscounted 2010 $]

Property damage + Property damage Travel delay travel delay

Rollover—Lower Bound ...... $7,713,841 $4,655,187 $12,369,028 Rollover—Upper Bound ...... 10,735,872 6,475,446 17,211,318 Loss of Control ...... 3,006,977 1,765,804 4,772,781

Total—Lower Bound ...... 10,720,818 6,420,991 17,141,809

Total–Upper Bound ...... 13,742,849 8,241,250 21,984,099

D. Cost Estimate incremental cost of installing an ESC systems. Accordingly, 57.8 percent of system instead of an RSC system is $520 truck tractors and 20 percent of buses The cost of this proposal is derived per vehicle. The agency did not receive would be required to be equipped with from the product of the average unit cost cost information from large bus an ESC system and 16.5 percent of truck of an ESC system and the number of manufacturers. However, because the tractors would be required to upgrade vehicles affected by this proposal. The components used on truck tractors and from an RSC system to an ESC system. number of vehicles affected by this buses are nearly identical, the unit cost Table 9 summarizes the costs of this proposal would include vehicles that estimates for truck tractors are used for would have no stability control systems buses. proposal based on the estimated unit and vehicles that would be equipped The agency has estimated that cost of an ESC system and the number with RSC systems. Therefore, when 150,000 truck tractors and 2,200 buses of vehicles that would need to be considering vehicles equipped with RSC covered by this proposal would be equipped with ESC systems. As shown systems, the average cost would be the produced in model year 2012. As stated in Table 10, the incremental cost of difference between the cost of an ESC earlier, the agency estimates that 26.2 providing ESC systems compared to system and the cost of an RSC system. percent of truck tractors and 80 percent manufacturers’ planned production in Based upon data received from of buses covered by this proposal model year 2012 would cost $113.1 manufacturers, the agency estimates that manufactured in model year 2012 million for truck tractors and $0.5 the average unit cost for an ESC system would be equipped with ESC systems. million for large buses. Therefore, the is $1,160 and the average unit cost for In addition, 16.5 percent of truck total cost of this proposal is estimated an RSC system is $640; therefore, the tractors would be equipped with RSC to be $113.6 million.

TABLE 9—ANNUAL TOTAL COSTS FOR THE PROPOSAL [2010 $]

Technology upgrade needed None Incremental ESC ESC

Truck Tractors: % Needing Upgrade ...... 26.2% 16.0% 57.8% 150,000 Sales Estimated ...... 39,300 24,000 86,700 Costs per Affected Vehicle ...... 0 $520 $1,160

Total Costs ...... 0 $12.5 M $100.6 M Large Buses: % Needing Upgrade ...... 80% 0% 20% 2,200 Sales Estimated ...... 1,760 0 440 Costs per Affected Vehicle ...... 0 $520 $1,160

Total Costs ...... 0 0 $0.5 M M: million.

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TABLE 10—SUMMARY OF VEHICLE We have estimated the cost to conduct E. Cost Effectiveness COSTS the proposed test maneuvers. We Safety benefits can occur at any time [2010 $] believe that the execution of the proposed SIS and SWD maneuvers during the vehicle’s lifetime. Therefore, the benefits are discounted at both 3 and Average would cost approximately $15,000 per vehicle Total test, assuming access to test facilities, 7 percent to reflect their values in 2010 costs costs tracks, and vehicles. Because it is not dollars, as reflected in Table 11. Table possible to anticipate how many tests 11 also shows that the net cost per Truck Tractors ...... $753.7 $113.1 M manufacturers might choose to run to equivalent life saved from this proposal Large Buses ...... 232.0 0.5 M certify a specific make, model, and ranged from $1.5 to $2.0 million at a 3 configuration, the agency cannot percent discount rate and from $2.0 to Total ...... 746.1 113.6 M estimate the total compliance costs for $2.6 million at a 7 percent discount rate. M: million. manufacturers. However, compliance The net benefits of this proposal are costs are implicitly included in the estimated to range from $228 to $310 We also note that manufacturers may estimated consumer cost, which million at a 3 percent discount rate and incur costs to certify their vehicles as includes a 150% markup to account for from $155 to $222 million at a 7 percent compliant with the proposed standard. fixed and overhead costs. discount rate.

TABLE 11—SUMMARY OF COST-EFFECTIVENESS AND NET BENEFITS BY DISCOUNT RATE [2010 $]

3% Discount 7% Discount

Low High Low High

Fatal Equivalents ...... 51 63 40 50 Injury Benefits ...... $328,197,087 $405,419,931 $257,409,480 $321,761,850 Property Damage and Travel Delay Savings ...... $13,862,581 $17,778,541 $11,006,756 $14,115,990 Vehicle Costs * ...... $113,562,400 $113,562,400 $113,562,400 $113,562,400 Net Costs ...... $99,699,819 $95,783,859 $102,555,644 $99,446,410 Net Cost Per Fatal Equivalent ...... $1,954,898 $1,520,379 $2,563,891 $1,988,928 Net Benefits ...... $228,497,268 $309,636,072 $154,853,836 $222,315,440 * Vehicle costs are not discounted, since they occur when the vehicle is purchased, whereas benefits occur over the vehicle’s lifetime and are discounted back to the time of purchase.

F. Comparison of Regulatory systems are less effective than ESC whereas ESC systems are estimated to Alternatives systems. Overall for the target crash cost $1,160 per unit. Furthermore, only population, our research has indicated approximately 57.8% of truck tractors The agency considered two that RSC systems have a 21 to 30 would be required to install RSC alternatives to the proposal. The first percent effectiveness rate, whereas ESC systems based on the data discussed alternative was requiring RSC systems systems have a 28 to 36 percent earlier regarding manufacturers’ plans. be installed on all newly manufactured effectiveness rate. An RSC system is A summary of the cost effectiveness of truck tractors and buses covered by this only slightly less effective at preventing RSC systems is set forth in Table 12. proposal. The second alternative was rollover crashes than an ESC system (37 When comparing this alternative to the requiring RSC systems be installed on to 53 percent versus 40 to 56 percent regulatory proposal, requiring RSC all newly manufactured trailers. effective, respectively), but it is much systems rather than ESC systems would Regarding the first alternative, less effective at preventing loss of be slightly more cost effective. However, requiring RSC systems be installed on control crashes (3 percent versus 14 this alternative would save fewer lives truck tractors and large buses, our percent). However, RSC systems are and have lower net benefits than this research has concluded that RSC only estimated to cost $640 per unit, proposal.

TABLE 12—SUMMARY OF COST-EFFECTIVENESS AND NET BENEFITS BY DISCOUNT RATE ALTERNATIVE 1—REQUIRING TRACTOR-BASED RSC SYSTEMS [2010 $]

3% Discount 7% Discount Low High Low High

Fatal Equivalents ...... 31 43 24 34 Injury Benefits ...... $199,492,347 $276,715,191 $154,445,688 $218,798,058 Property Damage and Travel Delay Savings ...... $9,714,383 $13,649,563 $7,713,126 $10,837,621 Vehicle Costs* ...... $55,769,600 $55,769,600 $55,769,600 $55,769,600 Net Costs...... $46,055,217 $42,120,037 $48,056,474 $44,931,979 Net Cost Per Fatal Equivalent ...... $1,485,652 $979,536 $2,002,353 $1,321,529 Net Benefits ...... $153,437,130 $234,595,154 $106,389,214 $173,866,079 * Vehicle costs are not discounted, since they occur when the vehicle is purchased, whereas benefits occur over the vehicle’s lifetime and are discounted back to the time of purchase.

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The second alternative considered trailer-based RSC systems in preventing Table 13 sets forth a summary of the was requiring trailer-based RSC systems rollover crashes is 7 to 10 percent. cost effectiveness of trailer-based RSC to be installed on all newly Therefore, the benefits of trailer-based systems. Because the operational life of manufactured trailers. Trailer-based RSC systems in preventing rollover are a trailer (approximately 45 years) is RSC systems would only be expected to about 17.2 percent of tractor-based ESC much longer than that of a truck tractor, prevent rollover crashes. Based on systems. it would take longer for trailer-based 2006–2008 GES data, 98 percent of the The agency estimates that about RSC systems to fully penetrate the fleet target truck-tractor crashes involve truck than it would for any tractor-based tractors with trailers attached. 203,000 new trailers are manufactured each year. Further, based on information system. Therefore, when the benefits of Therefore, the base crash population trailer-based RSC systems are would be 98 percent of Base 1 discussed from manufacturers, the agency discounted at a 3 and 7 percent rate, above. estimates that a trailer-based RSC As discussed in the proposal, it system would cost $400 per trailer. there is a much higher discount factor. became apparent during testing that Available data indicates that less than As can be seen in Table 13, this results trailer-based stability control systems 0.2 percent of the current annual in this alternative having negative net were less effective than tractor-based production of trailers comes with RSC benefits and a high cost per life saved. systems because trailer-based systems systems installed. Assuming all new Also, this alternative would have no could only control the trailer’s brakes. trailers would be required to install effect on buses. Accordingly, the agency Based upon the agency’s test data, it is RSC, the cost of this alternative is does not favor this alternative. estimated that the effectiveness of estimated to be $81.2 million.

TABLE 13—SUMMARY OF COST-EFFECTIVENESS AND NET BENEFITS BY DISCOUNT RATE ALTERNATIVE 2—REQUIRING TRAILER-BASED RSC SYSTEMS [2010 $]

At 3% Discount At 7% Discount Low High Low High

Fatal Equivalents ...... 5 7 3 5 Injury Benefits...... $30,754,672 $43,935,246 $20,700,937 $29,572,767 Property Damage and Travel Delay Savings ...... $1,459,169 $2,038,560 $982,165 $1,372,153 Vehicle Costs* ...... $81,200,000 $81,200,000 $81,200,000 $81,200,000 Net Costs...... $79,740,831 $79,161,440 $80,217,835 $79,827,847 Net Cost Per Fatal Equivalent ...... $15,948,166 $11,308,777 $26,739,278 $15,965,569 Net Benefits ...... ¥$48,986,159 ¥$35,226,194 ¥$59,516,898 ¥$50,255,080 * Vehicle costs are not discounted, since they occur when the vehicle is purchased, whereas benefits occur over the vehicle’s lifetime and are discounted back to the time of purchase.

The information in Tables 12 and 13 and annualized costs and benefits of can be contrasted with this proposal. A this proposal appears in Table 14. summary of the total costs and benefits

TABLE 14—ESTIMATED TOTAL COSTS AND BENEFITS OF THE PROPOSAL [In millions of 2010 dollars]

Property damage Cost per Total costs Injury benefits and travel delay equivalent live Net benefits savings saved

At 3% Discount ...... $113.6 $328–$405 $13.9–$17.8 $1.5–$2.0 $228–$310 At 7% Discount ...... 113.6 257–322 11.0–14.1 2.0–2.6 155–222

VII. Public Participation attach necessary additional documents comments, enclose a self-addressed, to your comments. There is no limit on stamped postcard in the envelope How do I prepare and submit the length of the attachments. containing your comments. Upon comments? Please submit two copies of your receiving your comments, Docket Your comments must be written and comments, including the attachments, Management will return the postcard by in English. To ensure that your to Docket Management at the beginning mail. comments are correctly filed in the of this document, under ADDRESSES. How do I submit confidential business Docket, please include the docket You may also submit your comments information? number of this document in your electronically to the docket following comments. the steps outlined under ADDRESSES. If you wish to submit any information Your comments must not be more How can I be sure that my comments under a claim of confidentiality, you than 15 pages long (49 CFR 553.21). We were received? should submit the following to the established this limit to encourage you NHTSA Office of Chief Counsel (NCC– to write your primary comments in a If you wish Docket Management to 110), 1200 New Jersey Avenue SE., concise fashion. However, you may notify you upon its receipt of your Washington, DC 20590: (1) A complete

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copy of the submission; (2) a redacted recommend that you periodically search of the rulemakings could be coordinated copy of the submission with the the Docket for new material. to lessen the need for multiple redesign confidential information removed; and and to lower overall costs. After this VIII. Regulatory Analyses and Notices (3) either a second complete copy or examination, we decided on a course of those portions of the submission A. Executive Order 12866, Executive action that prioritized the goal of containing the material for which Order 13563, and DOT Regulatory reducing passenger ejection and confidential treatment is claimed and Policies and Procedures increasing frontal impact protection any additional information that you NHTSA has considered the impact of because many benefits could be deem important to the Chief Counsel’s this rulemaking action under Executive achieved expeditiously with consideration of your confidentiality Order 12866, Executive Order 13563, countermeasures that were readily claim. A request for confidential and the Department of Transportation’s available (using bus seats with integral seat belts, which are already available treatment that complies with 49 CFR regulatory policies and procedures. This from seat suppliers) and whose Part 512 must accompany the complete rulemaking is considered economically installation would not significantly submission provided to the Chief significant and was reviewed by the impact other vehicle designs. Similarly, Counsel. For further information, Office of Management and Budget under we have also determined that an ESC submitters who plan to request E.O. 12866, ‘‘Regulatory Planning and rulemaking would present relatively few confidential treatment for any portion of Review.’’ The rulemaking action has synchronization issues with other rules, their submissions are advised to review also been determined to be significant because the vehicles at issue already 49 CFR part 512, particularly those under the Department’s regulatory have the foundation braking systems sections relating to document policies and procedures. NHTSA has needed for the stability control submission requirements. Failure to placed in the docket a Preliminary technology and the additional adhere to the requirements of Part 512 Regulatory Impact Analysis (PRIA) equipment necessary for an ESC system may result in the release of confidential describing the benefits and costs of this are sensors that are already available information to the public docket. In rulemaking action. The benefits and and that can be installed without addition, you should submit two copies costs are summarized in section VI of significant impact on other vehicle from which you have deleted the this preamble. claimed confidential business Consistent with Executive Order systems. Further, we estimate that 80 information, to Docket Management at 13563 and to the extent permitted under percent of the affected buses already the address given at the beginning of the Vehicle Safety Act, we have have ESC systems. We realize that a this document under ADDRESSES. considered the cumulative effects of the rollover structural integrity rulemaking, or an emergency egress rulemaking, Will the Agency consider late new regulations stemming from NHTSA’s 2007 ‘‘NHTSA’s Approach to could involve more redesign of vehicle comments? structure than rules involving systems Motorcoach Safety’’ plan and DOT’s 59 We will consider all comments that 2009 Motorcoach Safety Action Plan, such as seat belts, ESC, or tires. Our Docket Management receives before the and have taken steps to identify decision-making in these and all the close of business on the comment opportunities to harmonize and rulemakings outlined in the ‘‘NHTSA’s closing date indicated at the beginning streamline those regulations. By Approach to Motorcoach Safety’’ plan of this notice under DATES. In coordinating the timing and content of and DOT’s Motorcoach Safety Action accordance with our policies, to the the rulemakings, our goal is to Plan will be cognizant of the timing and extent possible, we will also consider expeditiously maximize the net benefits content of the actions so as to simplify comments that Docket Management of the regulations (by either increasing requirements applicable to the public receives after the specified comment benefits or reducing costs or a and private sectors, ensure that closing date. If Docket Management combination of the two) while requirements are justified, and increase receives a comment too late for us to simplifying requirements on the public the net benefits of the resulting safety consider in developing the proposed and ensuring that the requirements are standards. rule, we will consider that comment as justified. We seek to ensure that this B. Regulatory Flexibility Act an informal suggestion for future coordination will also simplify the rulemaking action. Pursuant to the Regulatory Flexibility implementation of multiple Act (5 U.S.C. 601 et seq., as amended by How can I read the comments submitted requirements on a single industry. the Small Business Regulatory by other people? NHTSA’s Motorcoach Safety Action Enforcement Fairness Act (SBREFA) of Plan identified four priority areas— 1996), whenever an agency is required You may read the comments received passenger ejection, rollover structural by Docket Management at the address to publish a notice of rulemaking for integrity, emergency egress, and fire any proposed or final rule, it must and times given near the beginning of safety. There have been other initiatives this document under ADDRESSES. prepare and make available for public on large bus performance, such as ESC comment a regulatory flexibility You may also see the comments on systems—an action included in the DOT analysis that describes the effect of the the Internet. To read the comments on plan—and an initiative to update the rule on small entities (i.e., small the Internet, go to http:// 58 large bus tire standard. In deciding businesses, small organizations, and www.regulations.gov and follow the on- how best to initiate and coordinate small governmental jurisdictions). The line instructions provided. rulemaking in these areas, NHTSA Small Business Administration’s You may download the comments. examined various factors including the regulations at 13 CFR Part 121 define a The comments are imaged documents, benefits that would be achieved by the small business, in part, as a business in either TIFF or PDF format. Please rulemakings, the anticipated vehicle entity ‘‘which operates primarily within note that even after the comment closing designs and countermeasures needed to the United States.’’ (13 CFR 121.105(a)). date, we will continue to file relevant comply with the regulations, and the information in the Docket as it becomes extent to which the timing and content 59 The initiative on fire safety is in a research available. Further, some people may phase. Rulemaking resulting from the research will submit late comments. Accordingly, we 58 75 FR 60037 (Sept. 29, 2010). not occur in the near term.

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No regulatory flexibility analysis is common law.’’ 49 U.S.C. 30103(e). ‘‘Civil Justice Reform’’ (61 FR 4729; Feb. required if the head of an agency Pursuant to this provision, State 7, 1996), requires that Executive certifies the rule will not have a common law tort causes of action agencies make every reasonable effort to significant economic impact on a against motor vehicle manufacturers ensure that the regulation: (1) Clearly substantial number of small entities. that might otherwise be preempted by specifies the preemptive effect; (2) SBREFA amended the Regulatory the express preemption provision are clearly specifies the effect on existing Flexibility Act to require Federal generally preserved. However, the Federal law or regulation; (3) provides agencies to provide a statement of the Supreme Court has recognized the a clear legal standard for affected factual basis for certifying that a rule possibility, in some instances, of conduct, while promoting simplification implied preemption of such State will not have a significant economic and burden reduction; (4) clearly impact on a substantial number of small common law tort causes of action by specifies the retroactive effect, if any; (5) entities. virtue of NHTSA’s rules, even if not NHTSA has considered the effects of expressly preempted. This second way specifies whether administrative this NPRM under the Regulatory that NHTSA rules can preempt is proceedings are to be required before Flexibility Act. I certify that this NPRM dependent upon there being an actual parties file suit in court; (6) adequately will not have a significant economic conflict between an FMVSS and the defines key terms; and (7) addresses impact on a substantial number of small higher standard that would effectively other important issues affecting clarity entities. This proposed rule would be imposed on motor vehicle and general draftsmanship under any directly impact manufacturers of truck- manufacturers if someone obtained a guidelines issued by the Attorney tractors, large buses, and stability State common law tort judgment against General. This document is consistent control systems for those vehicles. the manufacturer, notwithstanding the with that requirement. NHTSA believes these entities do not manufacturer’s compliance with the Pursuant to this Order, NHTSA notes qualify as small entities. NHTSA standard. Because most NHTSA as follows. The issue of preemption is C. Executive Order 13132 (Federalism) standards established by an FMVSS are discussed above. NHTSA notes further minimum standards, a State common that there is no requirement that NHTSA has examined today’s final law tort cause of action that seeks to individuals submit a petition for rule pursuant to Executive Order 13132 impose a higher standard on motor (64 FR 43255, August 10, 1999) and vehicle manufacturers will generally not reconsideration or pursue other concluded that no additional be preempted. However, if and when administrative proceedings before they consultation with States, local such a conflict does exist—for example, may file suit in court. governments or their representatives is when the standard at issue is both a E. Protection of Children From mandated beyond the rulemaking minimum and a maximum standard— Environmental Health and Safety Risks process. The agency has concluded that the State common law tort cause of the rulemaking would not have action is impliedly preempted. See Executive Order 13045, ‘‘Protection of sufficient federalism implications to Geier v. American Honda Motor Co., Children from Environmental Health warrant consultation with State and 529 U.S. 861 (2000). and Safety Risks’’ (62 FR 19855, April local officials or the preparation of a Pursuant to Executive Order 13132 23, 1997), applies to any rule that: (1) federalism summary impact statement. and 12988, NHTSA has considered Is determined to be ‘‘economically The final rule would not have whether this rule could or should significant’’ as defined under Executive ‘‘substantial direct effects on the States, preempt State common law causes of Order 12866, and (2) concerns an on the relationship between the national action. The agency’s ability to announce government and the States, or on the environmental, health, or safety risk that its conclusion regarding the preemptive the agency has reason to believe may distribution of power and effect of one of its rules reduces the have a disproportionate effect on responsibilities among the various likelihood that preemption will be an children. If the regulatory action meets levels of government.’’ issue in any subsequent tort litigation. NHTSA rules can preempt in two To this end, the agency has examined both criteria, the agency must evaluate ways. First, the National Traffic and the nature (e.g., the language and the environmental health or safety Motor Vehicle Safety Act contains an structure of the regulatory text) and effects of the planned rule on children, express preemption provision: When a objectives of today’s rule and finds that and explain why the planned regulation motor vehicle safety standard is in effect this rule, like many NHTSA rules, is preferable to other potentially under this chapter, a State or a political prescribes only a minimum safety effective and reasonably feasible subdivision of a State may prescribe or standard. As such, NHTSA does not alternatives considered by the agency. continue in effect a standard applicable intend that this rule preempt state tort This notice is part of a rulemaking to the same aspect of performance of a law that would effectively impose a that is not expected to have a motor vehicle or motor vehicle higher standard on motor vehicle disproportionate health or safety impact equipment only if the standard is manufacturers than that established by on children. Consequently, no further identical to the standard prescribed today’s rule. Establishment of a higher analysis is required under Executive under this chapter. 49 U.S.C. standard by means of State tort law Order 13045. 30103(b)(1). It is this statutory command would not conflict with the minimum by Congress that preempts any non- standard announced here. Without any F. Paperwork Reduction Act identical State legislative and conflict, there could not be any implied administrative law addressing the same preemption of a State common law tort Under the Paperwork Reduction Act aspect of performance. cause of action. of 1995 (PRA), a person is not required The express preemption provision to respond to a collection of information described above is subject to a savings D. Executive Order 12988 (Civil Justice by a Federal agency unless the clause under which ‘‘[c]ompliance with Reform) collection displays a valid OMB control a motor vehicle safety standard With respect to the review of the number. There is not any information prescribed under this chapter does not promulgation of a new regulation, collection requirement associated with exempt a person from liability at section 3(b) of Executive Order 12988, this NPRM.

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G. National Technology Transfer and H. Unfunded Mandates Reform Act paragraphing) make the rule easier to Advancement Act Section 202 of the Unfunded understand? • Would more (but shorter) sections Mandates Reform Act of 1995 (UMRA) Section 12(d) of the National be better? Technology Transfer and Advancement requires federal agencies to prepare a • Could we improve clarity by Act (NTTAA) requires NHTSA to written assessment of the costs, benefits, addling tables, lists, or diagrams? and other effects of proposed or final evaluate and use existing voluntary • What else could we do to make the rules that include a Federal mandate consensus standards in its regulatory rule easier to understand? likely to result in the expenditure by activities unless doing so would be If you have any responses to these State, local, or tribal governments, in the inconsistent with applicable law (e.g., questions, please include them in your aggregate, or by the private sector, of comments on this proposal. the statutory provisions regarding more than $100 million annually NHTSA’s vehicle safety authority) or (adjusted for inflation with base year of K. Regulatory Identifier Number (RIN) otherwise impractical. Voluntary 1995). Before promulgating a NHTSA The Department of Transportation consensus standards are technical rule for which a written statement is assigns a regulation identifier number standards developed or adopted by needed, section 205 of the UMRA (RIN) to each regulatory action listed in voluntary consensus standards bodies. generally requires the agency to identify the Unified Agenda of Federal Technical standards are defined by the and consider a reasonable number of Regulations. The Regulatory Information NTTAA as ‘‘performance-based or regulatory alternatives and adopt the Service Center publishes the Unified design-specific technical specification least costly, most cost-effective, or least Agenda in April and October of each and related management systems burdensome alternative that achieves year. You may use the RIN contained in practices.’’ They pertain to ‘‘products the objectives of the rule. The the heading at the beginning of this and processes, such as size, strength, or provisions of section 205 do not apply document to find this action in the technical performance of a product, when they are inconsistent with Unified Agenda. process or material.’’ applicable law. Moreover, section 205 L. Privacy Act Examples of organizations generally allows the agency to adopt an regarded as voluntary consensus alternative other than the least costly, Anyone is able to search the electronic form of all comments standards bodies include ASTM most cost-effective, or least burdensome received into any of our dockets by the International, the Society of Automotive alternative if the agency publishes with name of the individual submitting the Engineers (SAE), and the American the final rule an explanation of why that comment (or signing the comment, if National Standards Institute (ANSI). If alternative was not adopted. This NPRM will not result in any submitted on behalf of an association, NHTSA does not use available and expenditure by State, local, or tribal business, labor union, etc.). You may potentially applicable voluntary governments or the private sector of review DOT’s complete Privacy Act consensus standards, we are required by more than $100 million, adjusted for Statement in the Federal Register the Act to provide Congress, through inflation. When $100 million is adjusted published on April 11, 2000 (65 FR OMB, an explanation of the reasons for by the implicit gross domestic product 19477–78). not using such standards. price deflator for the year 2010, the List of Subjects in 49 CFR Part 571 This NPRM proposes to require truck result is $136 million. This NPRM is not tractors and large buses to have subject to the requirements of sections Imports, Incorporation by reference, electronic stability control systems. In 202 and 205 of the UMRA because it is Motor vehicle safety, Motor vehicles, the proposed definitional requirement, not estimated to result in an Rubber and rubber products, and Tires. the agency adapted the criteria from the expenditure of more than $136 million Proposed Regulatory Text annually by State, local, or tribal light vehicle ESC rulemaking, which In consideration of the foregoing, we governments or the private sector. was based on (with minor propose to amend 49 CFR part 571 to modifications) SAE Surface Vehicle I. National Environmental Policy Act read as follows: Information Report on Automotive Stability Enhancement Systems J2564 NHTSA has analyzed this rulemaking PART 571—FEDERAL MOTOR Rev JUN2004 that provides an industry action for the purposes of the National VEHICLE SAFETY STANDARDS consensus definition of an ESC system. Environmental Policy Act. The agency 1. The authority citation for part 571 In addition, SAE International has a has determined that implementation of continues to read as follows: Recommended Practice on Brake this action will not have any significant impact on the quality of the human Systems Definitions—Truck and Bus, Authority: 49 U.S.C. 322, 30111, 30115, environment. J2627 AUG2009 that has been 30166 and 30177; delegation of authority at 49 CFR 1.50. incorporated into the agency’s J. Plain Language 2. Revise paragraphs (d)(32) and definition. The agency has also Executive Order 12866 requires each (d)(33) of § 571.5 to read as follows: incorporated by reference two ASTM agency to write all rules in plain standards in order to provide language. Application of the principles § 571.5 Matter incorporated by reference. specifications for the road test surface. of plain language includes consideration * * * * * These are: (1) ASTM E1136–93 of the following questions: (d) * * * (Reapproved 2003), ‘‘Standard • Have we organized the material to (32) ASTM E1136–93 (Reapproved Specification for a Radial Standard suit the public’s needs? 2003), ‘‘Standard Specification for a Reference Test Tire,’’ and (2) ASTM • Are the requirements in the rule Radial Standard Reference Test Tire,’’ E1337–90 (Reapproved 2008), clearly stated? approved March 15, 1993, into ‘‘Standard Test Method for Determining • Does the rule contain technical §§ 571.105; 571.121; 571.126; 571.135; Longitudinal Peak Braking Coefficient of language or jargon that isn’t clear? 571.136; 571.139; 571.500. Paved Surfaces Using a Standard • Would a different format (grouping (33) ASTM E1337–90 (Reapproved Reference Test Tire.’’ and order of sections, use of headings, 2008), ‘‘Standard Test Method for

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Determining Longitudinal Peak Braking and at least one rear axle of the vehicle vertical axis through the vehicle’s center Coefficient of Paved Surfaces Using a to induce correcting yaw moment to of gravity. Standard Reference Test Tire,’’ limit vehicle oversteer and to limit S5. Requirements. Each vehicle must approved June 1, 2008, into §§ 571.105; vehicle understeer; be equipped with an ESC system that 571.121; 571.126; 571.135; 571.136; (2) That enhances rollover stability by meets the requirements specified in S5 571.500. applying and adjusting the vehicle brake under the test conditions specified in S6 * * * * * torques individually at each wheel and the test procedures specified in S7 3. Revise the heading of § 571.126 to position on at least one front and at least of this standard. read as follows: one rear axle of the vehicle to reduce S5.1 Required Equipment. Each lateral acceleration of a vehicle; vehicle to which this standard applies § 571.126 Standard No. 126; Electronic (3) That is computer-controlled with must be equipped with an electronic stability control systems for light vehicles. the computer using a closed-loop stability control system, as defined in * * * * * algorithm to induce correcting yaw S4. 4. Add § 571.136 to read as follows: moment and enhance rollover stability; S5.2 System Operational (4) That has a means to determine the Capabilities. § 571.136 Standard No. 136; Electronic vehicle’s lateral acceleration; S5.2.1 An electronic stability control stability control systems for heavy vehicles. (5) That has a means to determine the system must be operational over the full S1. Scope. This standard establishes vehicle’s yaw rate and to estimate its speed range of the vehicle except at performance and equipment side slip or side slip derivative with vehicle speeds less than 20 km/h (12.4 requirements for electronic stability respect to time; mph), when being driven in reverse, or control (ESC) systems on heavy (6) That has a means to estimate during system initialization. vehicles. vehicle mass or, if applicable, S5.2.2 An electronic stability control S2. Purpose. The purpose of this combination vehicle mass; system must remain capable of standard is to reduce crashes caused by (7) That has a means to monitor driver activation even if the antilock brake rollover or by directional loss-of-control. steering inputs; system or traction control is also S3. Application. This standard (8) That has a means to modify engine activated. applies to truck tractors and buses with torque, as necessary, to assist the driver S5.3 Performance Requirements. a gross vehicle weight rating of greater in maintaining control of the vehicle S5.3.1 Slowly Increasing Steer than 11,793 kilograms (26,000 pounds). and/or combination vehicle; and Maneuver. During the slowly increasing However, it does not apply to: (9) That, when installed on a truck steer test maneuver performed under the (a) Any truck tractor or bus equipped tractor, has the means to provide brake test conditions of S6 and the test with an axle that has a gross axle weight pressure to automatically apply and procedure of S7.6, the vehicle with the rating (GAWR) of 29,000 pounds or modulate the brake torques of a towed ESC system enabled must satisfy the more; semi-trailer. engine torque reduction criteria of (b) Any truck tractor or bus that has Initial brake temperature means the S5.3.1.1. a speed attainable in 2 miles of not more average temperature of the service S5.3.1.1 The engine torque than 33 mph; brakes on the hottest axle of the vehicle reduction when measured 1.5 seconds (c) Any truck tractor that has a speed immediately before any stability control after the activation of the electronic attainable in 2 miles of not more than system test maneuver is executed. stability control system must be at least 45 mph, an unloaded vehicle weight Lateral acceleration means the 10 percent less than the engine torque that is not less than 95 percent of its component of the vector acceleration of requested by the driver. gross vehicle weight rating (GVWR), and a point in the vehicle perpendicular to S5.3.2 Sine With Dwell Maneuver. no capacity to carry occupants other the vehicle x axis (longitudinal) and During each sine with dwell maneuver than the driver and operating crew; parallel to the road plane. performed under the test conditions of (d) Any bus with fewer than 16 Oversteer means a condition in which S6 and the test procedure of S7.10, the designated seating positions (including the vehicle’s yaw rate is greater than the vehicle with the ESC system enabled the driver); yaw rate that would occur at the must satisfy the roll stability criteria of (e) Any bus with fewer than 2 rows of vehicle’s speed as result of the S5.3.2.1 and S5.3.2.2, the yaw stability passenger seats that are rearward of the Ackerman Steer Angle. criteria of S5.3.2.3 and S5.3.2.4, and the driver’s seating position and are Peak friction coefficient or PFC means responsiveness criterion of S5.3.2.5 forward-facing or can convert to the ratio of the maximum value of during each of those tests conducted forward-facing without the use of tools; braking test wheel longitudinal force to with a commanded steering wheel angle (f) School buses; and the simultaneous vertical force of 0.7A or greater, where A is the (g) Any urban transit buses sold for occurring prior to wheel lockup, as the steering wheel angle computed in operation as a common carrier in urban braking torque is progressively S7.6.2. transportation along a fixed route with increased. S5.3.2.1 The lateral acceleration frequent stops. Sideslip or side slip angle means the measured at 0.75 seconds after S4. Definitions. arctangent of the lateral velocity of the completion of steer of the sine with Ackerman Steer Angle means the center of gravity of the vehicle divided dwell steering input must not exceed 30 angle whose tangent is the wheelbase by the longitudinal velocity of the percent of the peak value of the lateral divided by the radius of the turn at a center of gravity. acceleration recorded during the 2nd very low speed. Understeer means a condition in half of the sine maneuver (including the Electronic stability control system or which the vehicle’s yaw rate is less than dwell period), i.e., from time 1 second ESC system means a system that has all the yaw rate that would occur at the after the beginning of steer to the of the following attributes: vehicle’s speed as result of the completion of steer during the same test (1) That augments vehicle directional Ackerman Steer Angle. run. stability by applying and adjusting the Yaw Rate means the rate of change of S5.3.2.2 The lateral acceleration vehicle brake torques individually at the vehicle’s heading angle measure in measured at 1.5 seconds after each wheel position on at least one front degrees per second of rotation about a completion of steer of the Sine With

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Dwell steering input must not exceed 10 locking system is turned to the ‘‘On’’ S6.1.2 The maximum wind speed is percent of the peak value of the lateral (‘‘Run’’) position when the engine is not no greater than 5 m/s (11mph). acceleration recorded during the 2nd running, or when the ignition locking S6.2 Road test surface. half of the sine maneuver (including the system is in a position between the S6.2.1 The tests are conducted on a dwell period), i.e., from time 1 second ‘‘On’’ (‘‘Run’’) and ‘‘Start’’ that is dry, uniform, solid-paved surface. after the BOS to the COS during the designated by the manufacturer as a Surfaces with irregularities and same test run. check position. undulations, such as dips and large S5.3.2.3 The yaw rate measured at S5.4.4 The ESC malfunction telltale cracks, are unsuitable. 0.75 seconds after completion of steer of need not be activated when a starter S6.2.2 The road test surface the Sine With Dwell steering input must interlock is in operation. produces a peak friction coefficient not exceed 40 percent of the peak value S5.4.5 The ESC malfunction telltale (PFC) of 0.9 when measured using an of the yaw rate recorded during the 2nd lamp must extinguish at the next American Society for Testing and half of the sine maneuver (including the ignition cycle after the malfunction has Materials (ASTM) E1136–93 dwell period), i.e., from time 1 second been corrected. (Reapproved 2003) standard reference after the BOS to the COS during the S5.5 ESC System Technical test tire (incorporated by reference,, in same test run. Documentation. To ensure that a vehicle accordance with ASTM Method E 1337– S5.3.2.4 The yaw rate measured at is equipped with an ESC system that 90 (Reapproved 2002), at a speed of 64.4 1.5 seconds after completion of steer of meets the definition of ‘‘ESC System’’ in km/h (40 mph), without water delivery the Sine With Dwell steering input must S4, the vehicle manufacturer must make (both documents incorporated by not exceed 15 percent of the peak value available to the agency, upon request, reference, see § 571.5). of the yaw rate recorded during the 2nd the following documentation: S6.2.3 The test surface has a half of the sine maneuver (including the S5.5.1 A system diagram that consistent slope between 0% and 1%. dwell period), i.e., from time 1 second identifies all ESC system hardware. The S6.3 Vehicle conditions. after the BOS to the COS during the diagram must identify what components S6.3.1 The ESC system is enabled same test run. are used to generate brake torques at for all testing, except for the ESC S5.3.2.5 The lateral displacement of each controlled wheel, determine Malfunction test in S7.11. the vehicle center of gravity with vehicle lateral acceleration and yaw S6.3.2 Test Weight. respect to its initial straight path must rate, estimate side slip or the side slip S6.3.2.1 Truck tractors. The be at least 2.13 meters (7 feet) for each derivative, monitor driver steering combined total weight of the truck truck tractor and at least 1.52 meters (5 inputs, and for a tractor, generate the tractor and control trailer (specified in feet) for each bus when computed 1.5 towed vehicle brake torques. S6.3.4) is 80 percent of the tractor seconds after the BOS. S5.5.2 A written explanation GVWR. The tractor is loaded with the S5.3.2.5.1 The computation of describing the ESC system basic fuel tanks filled to at least 75 percent lateral displacement is performed using operational characteristics. This capacity, test driver, test double integration with respect to time explanation must include a discussion instrumentation, and a ballasted control of the measurement of lateral of the system’s capability to apply brake trailer with outriggers. Center of gravity acceleration at the vehicle center of torques at each wheel, how the system of all ballast on the control trailer is gravity, as expressed by the formula: estimates vehicle mass, and how the located directly above the kingpin. The Lateral Displacement = ∫∫ AyCG dt system modifies engine torque during load distribution on non-steer axles is S5.3.2.5.2 Time t = 0 for the ESC system activation. The explanation adjusted so that it is proportional to the integration operation is the instant of must also identify the vehicle speed tractor’s respective rear axles GAWRs by steering initiation, known as the BOS. range and the driving phases adjusting the fifth wheel position, if S5.4 ESC System Malfunction (acceleration, deceleration, coasting, adjustable. If the fifth wheel of the truck Detection. Each vehicle shall be during activation of ABS or traction tractor cannot be adjusted without equipped with an indicator lamp, control) under which the ESC system exceeding a GAWR, ballast is reduced mounted in front of and in clear view can activate. so that axle load is equal to or less than of the driver, which is activated S5.5.3 A logic diagram that supports the GAWR, maintaining load whenever there is a malfunction that the explanation provided in S5.5.2. proportioning as close as possible to affects the generation or transmission of S5.5.4 Specifically for mitigating, specified proportioning. control or response signals in the avoiding, and preventing vehicle S6.3.2.2 Buses. A bus is loaded to a vehicle’s electronic stability control rollover, oversteer, and understeer simulated multi-passenger system. conditions, a discussion of the pertinent configuration. For this configuration the S5.4.1 The ESC malfunction telltale inputs to the computer or calculations bus is loaded with the fuel tanks filled must illuminate only when a within the computer and how its to at least 75 percent capacity, test malfunction exists and must remain algorithm uses that information and driver, test instrumentation and continuously illuminated for as long as controls ESC system hardware to limit simulated occupants in each of the the malfunction exists, whenever the these loss of control conditions. vehicle’s designated seating positions. ignition locking system is in the ‘‘On’’ S6. Test Conditions. The requirements The simulated occupant loads are (‘‘Run’’) position. of S5 shall be met by a vehicle when it attained by securing a 68-kg (150-lb) S5.4.2 The ESC Malfunction telltale is tested according to the conditions set water dummy in each of the test must be identified by the symbol shown forth in the S6. On vehicles equipped vehicle’s designated seating positions for ‘‘Electronic Stability Control System with automatic brake adjusters, the without exceeding the vehicle’s GVWR Malfunction’’ or the specified words or automatic brake adjusters must remain and each axle’s GAWR. If any rating is abbreviations listed in Table 1 of activated at all times. exceeded the ballast load is reduced Standard No. 101 (49 CFR 571.101). S6.1 Ambient conditions. until the respective rating or ratings are S5.4.3 The ESC malfunction telltale S6.1.1 The ambient temperature is no longer exceeded. must be activated as a check of lamp between 7 °C (45 °F) and 40 °C (104 S6.3.3 Transmission selector function either when the ignition °F). position. The transmission selector

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control is in a forward gear during all contact the rubbing surface of a drum or according to S7.6. For a vehicle on maneuvers. rotor. The second thermocouple is which a full FMVSS No. 121 S6.3.4 Control Trailer. installed at a depth of 0.080 inch and compliance test was performed, S6.3.4.1 The control trailer is an located within 1.0 inch immediately prior to executing any unbraked flatbed semi-trailer that has a circumferentially of the thermocouple slowly increasing steer or sine with single axle with a GAWR of 8,165 installed at 0.040 inch depth. For dwell maneuvers, the brakes are kilograms (18,000 pounds) and a length center-grooved shoes or pads, burnished using 40 brake application of 655 + 15 cm (258 + 6 inches) when thermocouples are installed within snubs from a speed of 64 km/h (40 mph) measured from the transverse centerline 0.125 inch to 0.250 inch of the groove to a speed of 32 km/h (20 mph), with of the axle to the centerline of the and as close to the center as possible. a target deceleration of approximately kingpin. S6.4 Selection of compliance 0.3g. After each brake application, S6.3.4.2 The center of gravity height options. Where manufacturer options accelerate to 64 km/h (40 mph) and of the ballast on the loaded control are specified, the manufacturer shall maintain that speed until making the trailer is less than 61 cm (24 inches) select the option by the time it certifies next brake application at a point 1 mile above the top of the tractor’s fifth wheel. the vehicle and may not thereafter select from the initial point of the previous S6.3.5 Tires. The vehicle is tested a different option for the vehicle. Each brake application. At end of the 40 with the tires installed on the vehicle at manufacturer shall, upon request from snubs, the hottest brake temperature is time of initial vehicle sale. The tires are the National Highway Traffic Safety confirmed to be within the temperature inflated to the vehicle manufacturer’s Administration, provide information range of 65 °C–204 °C (150 °F–400 °F). recommended cold tire inflation regarding which of the compliance If the hottest brake temperature is above pressure(s) specified on the vehicle’s options it has selected for a particular 204 °C (400 °F) a cool down period is certification label or the tire inflation vehicle or make/model. performed until the hottest brake pressure label. S7. Test Procedure. temperature is measured within that S6.3.6 Outrigger. An outrigger is S7.1 Tire inflation. Inflate the range. If the hottest brake temperature is used for testing each vehicle. The vehicle’s tires to the cold tire inflation below 65 °C (150 °F) individual brake outrigger is designed with a maximum pressure(s) provided on the vehicle’s stops shall be repeated to increase any weight of 726 kg (1,600 lb), excluding certification label or tire information one brake temperature to within the mounting fixtures. label. target temperature range of 65 °C–204°C S6.3.7 Automated steering machine. S7.2 Telltale lamp check. With the (150 °F–400 °F) before the subject A steering machine programmed to vehicle stationary and the ignition maneuver can be performed. execute the required steering pattern is locking system in the ‘‘Lock’’ or ‘‘Off’’ S7.6 Slowly Increasing Steer Test. used during the slowly increasing steer position, activate the ignition locking The vehicle is subjected to two series of and sine with dwell maneuvers. The system to the ‘‘On’’ (‘‘Run’’) position or, runs of the slowly increasing steer test steering machine is capable of where applicable, the appropriate using a constant vehicle speed of 48.3 supplying steering torques between 40 position for the lamp check. The ESC ± 1.6 km/h (30.0 ± 1.0 mph) and a to 60 Nm (29.5 to 44.3 lb-ft). The system must perform a check of lamp steering pattern that increases by 13.5 steering machine is able to apply these function for the ESC malfunction degrees per second until ESC system torques when operating with steering telltale, as specified in S5.3.3. activation is confirmed. Three wheel velocities up to 1200 degrees per S7.3 Mass Estimation Cycle. While repetitions are performed for each test second. driving in a straight line, one stop is series. One series uses counterclockwise S6.3.8 Truck Tractor Anti-jackknife performed from a speed of 65 km/h (40 steering, and the other series uses System. The truck tractor is equipped mph), with a target longitudinal clockwise steering. During each run ESC with anti-jackknife cables that allow a deceleration between 0.3–0.4g. activation is required for the Engine minimum articulation angle of 45 S7.4 Tire Conditioning. Condition Torque Reduction test and is confirmed degrees between the tractor and the the tires using the following procedure as specified in S7.7. control trailer. to wear away mold sheen and achieve S7.6.1 The slowly increasing steer S6.3.9 Special drive conditions. A operating temperature immediately maneuver sequence is started using a vehicle equipped with an interlocking before beginning the Brake commanded steering wheel angle of 270 axle system or a front wheel drive Conditioning, SIS and SWD maneuver degrees. If ESC activation did not occur system that is engaged and disengaged test runs. during the maneuver then the by the driver is tested with the system S7.4.1 The test vehicle is driven commanded steering wheel angle is disengaged. around a circle 46 meters (150 feet) in increased by 270 degree increments up S6.3.10 Liftable axles. A vehicle radius at a speed that produces a lateral to the vehicle’s maximum allowable with a liftable axle is tested with the acceleration of approximately 0.1g for steering angle or until ESC activation is liftable axle down. two clockwise laps followed by two confirmed. S6.3.11 Initial brake temperature. counterclockwise laps. S7.6.2 From the slowly increasing The initial brake temperature is not less S7.5 Brake Conditioning. steer tests, the quantity ‘‘A’’ is than 65 °C (150 °F) and not more than Conditioning and warm-up the vehicle determined. ‘‘A’’ is the steering wheel 204 °C (400 °F). brakes must be completed before and angle in degrees that is estimated to S6.3.12 Thermocouples. The brake during execution of the SIS and SWD produce a lateral acceleration of 0.5g for temperature is measured by plug-type maneuver test runs. the test vehicle. Utilizing linear thermocouples installed in the S7.5.1 Prior to executing the first regression on the lateral acceleration approximate center of the facing length series of SIS maneuvers for a test data recorded between 0.05g and 0.3g, and width of the most heavily loaded vehicle, the brakes are burnished and then linear extrapolation out to a shoe or disc pad, one per brake. A according to the procedure in S6.1.8 of lateral acceleration value of 0.5g, A is second thermocouple may be installed Standard No. 121, Air brake systems. calculated, to the nearest 0.1 degrees, at the beginning of the test sequence if S7.5.2 After the brakes are from each of the six satisfactory slowly the lining wear is expected to reach a burnished in accordance with S7.5.1, increasing steer tests. If ESC activation point causing the first thermocouple to initiate the vehicle compliance test occurs prior to the vehicle experiencing

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a lateral acceleration of 0.3g then the will diverge when ESC system are performed immediately prior to data used during the linear regression activation causes a commanded engine conducting the sine with dwell test. will be that data recorded between 0.05g torque reduction and the driver attempts S7.9 Check that the ESC system is and the lateral acceleration measured at to accelerate the vehicle maintaining the enabled by ensuring that the ESC the time of ESC activation. The absolute required constant test speed causing an malfunction telltale is not illuminated. value of the six A’s calculated is increased driver requested torque. averaged and rounded to the nearest 0.1 S7.7.1 During each of the six slowly S7.10 Sine With Dwell Test. The degrees to produce the final quantity, A, increasing steer test runs, verify the vehicle is subjected to two series of test used during the sine with dwell commanded engine torque and the runs using a steering pattern of a sine maneuvers below. driver requested torque signals diverge wave at 0.5 Hz frequency with a 1.0 sec S7.7 Engine Torque Reduction Test. at least 10 percent 1.5 seconds after the delay beginning at the second peak During each of the six completed slowly beginning of ESC activation occurs as amplitude as shown in Figure 1 (sine increasing steer test maneuvers, ESC defined in S7.12.15. with dwell maneuver). One series uses activation is confirmed by comparing S7.7.2 If ESC activation does not counterclockwise steering for the first the engine torque output and driver occur in all of the six slowly increasing half cycle, and the other series uses requested torque data collected from the steer test maneuvers the test is clockwise steering for the first half vehicle J1939 communication data link. terminated. cycle. Before each test run brake During the initial stages of each S7.8 After the quantity A has been temperatures are monitored and the maneuver the two torque signals with determined in S7.6, without replacing hottest brake is confirmed to be within respect to time will parallel each other. the tires, the tire and brake conditioning the temperature range of 65 °C–204 °C Upon ESC activation, the two signals procedures described in S7.4 and S7.5 (150 °F–400 °F).

S7.10.1 For manual transmissions, the final run shall be the 0.1A the ‘‘Start’’ position and start the engine. the steering motion is initiated with the amplitude that is closest or equal to, but Place the vehicle in a forward gear and vehicle coasting (dropped throttle) with not exceeding, 400 degrees. obtain a vehicle speed of 48.3 ± 8.0 km/ the clutch disengaged at 72.4 ± 1.6 km/ S7.10.5 Upon completion of the two h (30.0 ± 5.0 mph). Drive the vehicle for h (45.0 ± 1.0 mph). For automatic series of test runs, post processing of the at least two minutes including at least transmissions, the steering motion is yaw rate and lateral acceleration data to one left and one right turning maneuver initiated with the vehicle coasting and determine Lateral Acceleration Ratio and at least one service brake the transmission in the ‘‘drive’’ (LAR), Yaw Rate Ratio (YRR) and lateral application. Verify that within two selection position. displacement, is done as specified in minutes of obtaining this vehicle speed S7.10.2 In each series of test runs, S7.12. the ESC malfunction indicator the steering amplitude is increased from S7.11 ESC Malfunction Detection. illuminates in accordance with S5.3. run to run, by 0.1A, provided that no S7.11.1 Simulate one or more ESC S7.11.3 Stop the vehicle, deactivate such run will result in steering malfunction(s) by disconnecting the the ignition locking system to the ‘‘Off’’ amplitude greater than that of the final power source to any ESC component, or or ‘‘Lock’’ position. After a five-minute run specified in S7.10.4. disconnecting any electrical connection period, activate the vehicle’s ignition S7.10.3 The steering amplitude for between ESC components (with the locking system to the ‘‘Start’’ position the initial run of each series is 0.3A vehicle power off). When simulating an and start the engine. Verify that the ESC where A is the steering wheel angle ESC malfunction, the electrical malfunction indicator again illuminates determined in S7.6. connections for the telltale lamp(s) are to signal a malfunction and remains S7.10.4 The steering amplitude of not to be disconnected. illuminated as long as the engine is the final run in each series is the lesser S7.11.2 With the vehicle initially running or until the fault is corrected. of 1.3A or 400 degrees. If any 0.1A stationary and the ignition locking S7.11.4 Deactivate the ignition increment, up to 1.3A, is greater than system in the ‘‘Lock’’ or ‘‘Off’’ position, locking system to the ‘‘Off’’ or ‘‘Lock’’ 400 degrees, the steering amplitude of activate the ignition locking system to position. Restore the ESC system to

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normal operation, activate the ignition analog signal is filtered with a 0.1- S7.12.13 Determine lateral velocity system to the ‘‘Start’’ position and start second running average filter. by integrating corrected, filtered and the engine. Verify that the telltale has S7.12.7 Steering wheel velocity is zeroed lateral acceleration data. Zero extinguished. determined by differentiating the lateral velocity at BOS event. Determine S7.12 Post Data Processing— filtered steering wheel angle data. The lateral displacement by integrating Calculations for Performance Metrics. steering wheel velocity data is then zeroed later velocity. Zero lateral Engine torque reduction, lateral filtered with a moving 0.1-second displacement at BOS event. Lateral acceleration and yaw rate decay running average filter. displacement at 1.50 seconds from BOS calculations, and lateral responsiveness S7.12.8 Lateral acceleration, yaw event is determined by interpolation. checks must be processed utilizing the rate and steering wheel angle data S7.12.14 The ESC activation point is following techniques: channels are zeroed utilizing a defined the point where the measured driver S7.12.1 Raw steering wheel angle ‘‘zeroing range.’’ The ‘‘zeroing range’’ is demanded torque and the engine torque data is filtered with a 12-pole phaseless the 1.0-second time period prior to the first begin to deviate from one another Butterworth filter and a cutoff frequency instant the steering wheel velocity (engine torque decreases while driver of 10Hz. The filtered data is then zeroed exceeds 40 deg/sec. The instant the requested torque increases) during the to remove sensor offset utilizing static steering wheel velocity exceeds 40 deg/ slowly increasing steer maneuver. The pretest data. sec is the instant defining the end of the torque values are obtained directly from S7.12.2 Raw yaw, pitch and roll rate ‘‘zeroing range.’’ each vehicle’s SAE J1939 data is filtered with a 12-pole phaseless S7.12.9 The beginning of steer (BOS) communication data bus. Torque values Butterworth filter and a cutoff frequency is the first instance filtered and zeroed used to determine the ESC activation of 3 Hz. The filtered data is then zeroed steering wheel angle data reaches -5 point are interpolated. to remove sensor offset utilizing static degrees (when the initial steering input S8. Compliance Date. pretest data. is counterclockwise) or +5 degrees S8.1 Buses. All buses manufactured S7.12.3 Raw lateral acceleration data (when the initial steering input is on or after [date that is two years after is filtered with a 12-pole phaseless clockwise). The value for time at the publication of a final rule implementing Butterworth filter and a cutoff frequency BOS is interpolated. this proposal] must comply with this of 6Hz. The filtered data is then zeroed standard S7.12.10 The Completion of Steer to remove sensor offset utilizing static S8.2 Truck tractors. for the sine with dwell maneuver (COS) pretest data. The lateral acceleration S8.2.1 All two-axle and three-axle is the time the steering wheel angle data at the vehicle center of gravity is truck tractors with a front axle that has returns to zero. The value for time at the determined by removing the effects a GAWR of (14,600 pounds) or less and COS is interpolated. caused by vehicle body roll and by with two rear drive axles that have a correcting for sensor placement via use S7.12.11 The peak lateral combined GAWR of (45,000 pounds) or of coordinate transformation. For data acceleration is the maximum lateral less manufactured on or after [date that collection, the lateral accelerometer acceleration measured during the is two years after publication of a final shall be located as close as possible to second half of the sine maneuver, rule implementing this proposal] must the position of the vehicle’s longitudinal including the dwell period from 1.0 comply with this standard. and lateral centers of gravity. second after the BOS to the COS. The S8.2.2 All truck tractors S7.12.4 Raw vehicle speed data is lateral accelerations at 0.75 and 1.0 manufactured on or after [date that is filtered with a 12-pole phaseless seconds after COS are determined by four years after publication of a final Butterworth filter and a cutoff frequency interpolation. rule implementing this proposal] must of 2 Hz. S7.12.12 The peak yaw rate is the comply with this standard. S7.12.5 Left and right side ride maximum yaw rate measured during the height data is filtered with a 0.1-second second half of the sine maneuver, Issued: May 15, 2012. running average filter. including the dwell period from 1.0 Christopher J. Bonanti, S7.12.6 The J1939 torque data second after the BOS to the COS. The Associate Administrator for Rulemaking. collected as a digital signal does not get yaw rates at 0.75 and 1.0 seconds after [FR Doc. 2012–12212 Filed 5–16–12; 4:15 pm] filtered. J1939 torque collected as an COS are determined by interpolation. BILLING CODE 4910–59–P

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