U.S. Department Of Transportation PRELIMINARY ECONOMIC ASSESSMENT TIRE PRESSURE MONITORING SYSTEM FMVSS No. 138 Office of Regulatory Analysis and Evaluation Plans and Policy July 2001 Table of Contents Executive Summary....................................................................................................................i Introduction.............................................................................................................................I-1 Background and Alternatives ...............................................................................................II-1 Tire Pressure Survey and Test Results ................................................................................III-1 Target Population................................................................................................................. IV-1 Benefits ..................................................................................................................................V-1 Human Factors Issues ........................................................................................................V-1 Stopping Distance..............................................................................................................V-3 Fuel Economy .................................................................................................................V-40 Tread Life .......................................................................................................................V-46 Unquantifiable Benefits ...................................................................................................V-53 Costs and Lead Times.......................................................................................................... VI-1 Cost Effectiveness ..............................................................................................................VII-1 Small Business Impacts ....................................................................................................VIII-1 Cumulative Impacts ............................................................................................................. IX-1 Executive Summary As required by the Transportation Recall Enhancement, Accountability, and Documentation (TREAD) Act, the agency is proposing to require a Tire Pressure Monitoring System (TPMS) be installed in all passenger cars, multipurpose passenger vehicles, trucks and buses that have a Gross Vehicle Weight Rating of 10,000 pounds or less, effective in November 2003. Two alternatives are examined in this assessment: Alternative 1 would require that the driver be given a warning when tire pressure is 20 percent or more below the placard pressure for one to four tires. Alternative 2 would require that the driver be given a warning when tire pressure is 25 percent or more below the placard pressure for one to three tires. There are two basic types of TPMS, direct measurement systems that have a tire pressure sensor for each tire, and indirect measurement systems that determine tire inflation pressure from wheel speeds. We assume that a direct measurement system would be required to meet Alternative 1. The indirect measurement systems are designed for use with the anti-lock brake system (ABS) and compare the relative wheel speed of one wheel to another. Wheel speed correlates to tire pressure since the diameter of a tire goes down slightly with low tire pressure. Since the indirect measurement system compares relative wheel speed, it cannot determine when all four tires lose air at about the same rate, thus Alternative 2 would require a warning when one to three tires lose pressure. We assume that vehicles which currently have an ABS system would use an indirect measurement system and vehicles without ABS would use a direct measurement system to meet Alternative 2. The agency conducted a large study of tire pressure at 336 gasoline stations around the country and estimates that Alternative 1 would result in 38 percent of light vehicle operators being warned of low tire pressure, while Alternative 2 would result in 24 percent of light vehicle operators being warned. Low tire pressure may have an influence on any crash that involves braking, since low tire pressure can result in reduced stopping distance. The quantified benefits, based on reduced stopping distance, have been estimated using two sets of data. One set of data indicates that benefits would be zero or insignificant. The second set of data indicates that there would be significant benefits from reduced stopping distance. Mid-point estimates from these two sets of data are: Annual Full Fleet Benefits of TPMS Injuries Reduced Fatalities Reduced (All AIS levels) Alternative 1 10,635 79 Alternative 2 6,585 49 DRAFT – DELIBERATIVE DOCUMENT – DO NOT RELEASE i There are unquantified benefits related to crashes caused by blowouts, stopped vehicles with flat tires, handling characteristics, and hydroplaning. An estimated 23,000 crashes and 535 fatal crashes annually involve blowouts or flat tires. Since the agency does not collect tire pressure during its crash investigations, the agency cannot estimate how many crashes are caused by the influence that low tire inflation has on blowouts, vehicle handling, and hydroplaning. Theory and limited testing show that low tire pressure has a significant impact on all of these. There are non-quantified costs and benefits that include the extra time it takes to inflate tires more frequently, the cost to replace batteries in some direct measurement systems, potential maintenance costs of TPMS, the property damage savings from avoiding crashes or reducing delta V in non-preventable crashes, and the savings in time and congestion from avoiding crashes. The estimated consumer cost increase for an average new vehicle would be $66.33 for Alternative 1 and $30.54 for Alternative 2. The net costs are estimated to be: Net Costs per Vehicle (2001 Dollars) Present Value Present Value of Tread Wear Net Costs Vehicle Costs of Fuel Savings Savings Alternative 1 $66.33 $32.22 $11.03 $23.08 Alternative 2 $30.54 $16.40 $5.51 $8.63 The net costs per equivalent life saved are estimated at the 7 percent discount rate to be: Net Cost per Equivalent Life Saved Alternative 1 $1.9 million Alternative 2 $1.1 million DRAFT – DELIBERATIVE DOCUMENT – DO NOT RELEASE ii These estimates are derived from the following: Total Annual Costs for 16 Million Vehicles (Millions of 2001 Dollars) Present Value Present Value of Tread Wear Net Costs Vehicle Costs of Fuel Savings Savings Alternative 1 $1,061 $516 $176 $369 Alternative 2 $489 $263 $88 $138 Present Discounted Value of Benefits Injuries Reduced Fatalities Reduced (All AIS levels) Alternative 1 7,038 52 Alternative 2 4,358 32 DRAFT – DELIBERATIVE DOCUMENT – DO NOT RELEASE iii I-1 I. INTRODUCTION The National Highway Traffic Safety Administration is evaluating a proposed new regulation that would require a tire pressure monitoring system (TPMS) on all passenger cars, light trucks (pickups, vans, and sport utility vehicles), and buses with a gross vehicle weight rating (GVWR) of 10,000 pounds or less (collectively this group is called “passenger vehicles” throughout this assessment). This is in accordance with the TREAD Act (H.R. 5164), Sec. 13. Tire Pressure Warning: “Not later than 1 year after the date of the enactment of this Act, the Secretary of Transportation shall complete a rulemaking for a regulation to require a warning system in new motor vehicles to indicate to the operator when a tire is significantly under-inflated. Such requirement shall become effective not later than 2 years after the date of the completion of such rulemaking.” This means that the agency must issue a final rule by November 1, 2001 and the effective date would be before November 1, 2003. II-1 II. BACKGROUND and ALTERNATIVES There are two types of Tire Pressure Monitoring Systems (TPMS) currently available that can alert the driver while driving that the tire pressure is low: direct measurement systems and indirect measurement systems. A direct measurement system measures tire pressure directly. A variation of the direct measurement system (a direct measurement system with a pump) will soon be available that can inflate the tire when it gets low, relieving the driver of that responsibility. An indirect measurement system measures wheel speed or something other than tire pressure. The current ABS-based systems are an indirect measurements system. They measure wheel speed and then compare the variance in wheel speed from one wheel to another. Direct measurement systems Most direct measurement systems have pressure and temperature sensors in each tire, usually attached to the inflation valve. They broadcast their data to a central receiver, or in some cases to individual antennae that transmit the data to the control module, which analyzes them and sends appropriate signals to a display). This display can be as simple as a single telltale, or as complex as pressure and temperature displays for all four tires (or five including the spare). Direct measurement systems advantages include: (1) much more sensitivity to small pressure losses, with claims ranging from +/- 0.1 psi to 1 psi; (2) the ability to directly measure pressure in any tire at any time, including before starting the vehicle, and including the spare tire. The disadvantages include: (1) the higher cost; (2) possible maintenance problems when tires are taken on and off the rim (sensors have been broken off). These systems