A Forward Collision Warning (Fcw) Performance Evaluation
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A FORWARD COLLISION WARNING (FCW) PERFORMANCE EVALUATION Garrick J. Forkenbrock National Highway Traffic Safety Administration United States of America Bryan C. O’Harra Transportation Research Center, Inc. United States of America Paper No. 09-0561 ABSTRACT At the time the work discussed in this paper was performed, the number of US-production light This paper describes tests performed by the National vehicles available with FCW was very low, with only Highway Traffic Safety Administration (NHTSA) to three vehicle manufacturers offering such systems on evaluate the forward collision warning (FCW) limited variants of certain vehicle makes and models. systems installed on three late model passenger cars. So as to best evaluate the current state of FCW NHTSA defines an FCW system as one intended to technology implementation, sample offerings from passively assist the driver in avoiding or mitigating a each of these vehicle manufacturers were procured: a rear-end collision via presentation of audible, visual, 2009 Acura RL, 2009 Mercedes S600, and a 2008 and/or haptic alerts, or any combination thereof. The Volvo S80. Although each of these vehicles present test maneuvers described were designed to emulate the driver with auditory and visual alerts, the manner the top three most common rear-end pre-crash in which these cues were presented differed, as scenarios reported in the 2004 GES database. shown in Table 1. FCW system performance was quantified by Table 1. specifying the average time-to-collision (TTC) FCW Alert Modality between the subject vehicle (SV) and principle other FCW Alert vehicle (POV) at the time of the SV’s FCW alert. Vehicle Visual Auditory BACKGROUND Message on instrument Acura RL Repeated beeps panel During the summer of 2008, the National Highway Traffic Safety Administration (NHTSA) performed Mercedes S600 Icon on instrument panel Repeated beeps an evaluation of the forward collision warning HUD using up to two Volvo S80 Repeated tones (FCW) systems installed on three late model sequences of red LEDs passenger cars. All tests were performed by researchers at the agency’s Vehicle Research and Test Center (VRTC), located on the Transportation THE REAR-END COLLISION CRASH Research Center, Inc. (TRC) proving grounds in East PROBLEM Liberty, OH. When determining what kinds of tests would be NHTSA defines an FCW system as one intended to appropriate for use in FCW evaluation, work passively assist the driver in avoiding or mitigating a performed by the agency’s Automotive Rear-End rear-end collision. FCW systems have forward- Collision Avoidance System (ACAS) project [1], the looking vehicle detection capability, provided by Integrated Vehicle-Based Safety Systems (IVBSS) technologies such as RADAR, LIDAR (laser), and Crash Avoidance Metrics Partnership (CAMP) cameras, etc. Using the information provided by programs [2,3], and research by the Volpe Center these sensors, an FCW system alerts the driver that a (part of DOT's Research and Innovative Technology collision with another vehicle in the anticipated Administration) [4] was reviewed. Based on 2004 forward pathway of their vehicle may be imminent General Estimates System (GES) statistics, a unless corrective action is taken. FCW system alerts summary performed by Volpe shows that overall, consist of audible, visual, and/or haptic warnings, or approximately 6,170,000 police-reported crashes of any combination thereof. all vehicle types, involving 10,945,000 vehicles, Forkenbrock 1 occurred in the United States. These statistics also Table 3. indicate that overall, all police-reported light-vehicle Crash Rankings By Cost (2004 GES data) crashes resulted in an estimated cost of $120 billion, Scenario Cost ($) Percent and functional years lost (a measure of harm) totaled approximately 2,767,000 [5]. These societal harm Lead Vehicle Stopped 15,388,000,000 12.8 measures were based on the GES crash sample and did not incorporate data from non-police-reported crashes. Lead Vehicle Decelerating 6,390,000,000 5.3 Lead Vehicle Moving at 3,910,000,000 3.3 Using the 37 crash typology described in [5], Volpe Lower Constant Speed identified that many of these crashes involved rear- end collision scenarios. Of the 37 groupings used to Table 4. describe the overall distribution of pre-crash scenario Crash Rankings By Functional Years Lost types, the Lead Vehicle Stopped, Lead Vehicle (2004 GES data) Decelerating, and Lead Vehicle Moving at Lower Constant Speed crashes represented in the 2004 GES Scenario Years Lost Percent database were found to be the 2nd, 4th, and 12th most common crash scenarios overall, respectively, Lead Vehicle Stopped 240,000 8.7 and were the top three rear-end pre-crash scenarios. Note that in 50% of Lead Vehicle Stopped crashes, Lead Vehicle Decelerating 100,000 3.6 the lead vehicle first decelerates to a stop and is then Lead Vehicle Moving at struck by the following vehicle, which typically 78000 2.8 happens in the presence of a traffic control device or Lower Constant Speed the lead vehicle is slowing down to make a turn. Tables 2 through 4 presents summaries of these rear- TEST METHODOLOGY end pre-crash scenarios, ranked by frequency, cost, and harm (expressed as functional years lost), Overview respectively. The tests described in this paper were designed to Based on the crash frequency, cost, and harm data evaluate the ability of an FCW system to detect and presented in Tables 2 through 4, NHTSA decided use alert drivers of potential hazards in the path of their of test maneuvers designed to emulate these real- vehicles. Three driving scenarios were used to world crash scenarios would provide an appropriate assess this technology. In the first test, a subject way to evaluate FCW performance. Building on the vehicle (SV) approached a stopped principle other efforts put forth by the ACAS and IVBSS programs, vehicle (POV) in the same lane of travel. The second NHTSA researchers subsequently developed three test began with the SV initially following the POV at objective test procedures to perform the work the same constant speed. After a short while, the described in this paper. The objectives of this work POV stopped suddenly. The third test consisted of were twofold: (1) identify the time-to-collision the SV, traveling at a constant speed, approaching a (TTC) values from the time an FCW alert was first slower moving POV, which was also being driven at presented to the driver, and (2) refine the test a constant speed. For the sake of brevity, these three procedures, as necessary, to enhance the accuracy, tests will be referred to as the “Lead Vehicle repeatability, and/or reproducibility by which the Stopped,” “Decelerating Lead Vehicle,” and “Slower FCW system evaluations could be performed. Moving Lead Vehicle” tests, respectively, for the remainder of this paper. Table 2. Crash Rankings By Frequency (2004 GES data) The tests were each performed on the TRC skid pad, a 3600 ft (1097 m) long flat (0.5 percent upwards Scenario Frequency Percent longitudinal slope, with a negligible cross slope) concrete roadway comprised of seven paved lanes. Lead Vehicle Stopped 975,000 16.4 The pavement of the skid pad lanes used for the FCW evaluations was in good condition, free from Lead Vehicle Decelerating 428,000 7.2 potholes, bumps, and cracks that could cause the subject vehicle to pitch excessively. Each lane was Lead Vehicle Moving at 210,000 3.5 Lower Constant Speed approximately 12 ft (3.7 m) wide, and was delineated with solid white pavement lines. All tests were Forkenbrock 2 performed during daylight hours with good visibility Use of an artificial POV would have introduced (no fog, rain, or snow) and very windy conditions significant test complexity for some tests. Although were avoided (wind speeds ranged from 0 to 17 mph NHTSA presently owns a full-size inflatable balloon during the testing timeline). The ambient car intended for used in collision avoidance/ temperatures present during test conduct ranged from mitigation testing, two of the three test scenarios 63 to 83 ºF (17 to 28 ºC). described in this paper required the POV accurately and consistently travel in a straight line at speeds up A 2008 Buick Lucerne was used as the POV for all to 45 mph. Additionally, the “SV approaches a FCW tests discussed in this paper. The vehicle, as decelerating POV” tests required the POV achieve shown in Figure 1, was selected to represent a and maintain a set deceleration magnitude. “typical” mid-sized passenger car. Use of an Development of a new artificial test apparatus able to artificial representation was considered (e.g., an accommodate these demands was outside of the inflatable or foam car), but ultimately not deemed scope of the project. necessary for three reasons: safety considerations, test consistency, and test complexity. Instrumentation Table 5 provides a summary of the instrumentation used during NHTSA’s FCW evaluations. The POV and each SV and were equipped with instrumentation and data acquisition systems. All analog data was sampled at 200 Hz. For the SV, vehicle speed, lateral and longitudinal position (via GPS), range to POV (via radar), yaw rate, and FCW alert status data were recorded. In the case of the Mercedes S600, FCW alert output from the high speed controller area Figure 1. Buick Lucerne (POV) and Mercedes network (CAN) also was collected using equipment S600 (SV) during an FCW test performed on discussed in the next section. For the POV, vehicle the TRC skidpad. speed, position, brake pedal travel, and longitudinal acceleration data were collected. Signal The evaluations discussed in this paper were intended conditioning of these data consisted of amplification, to evaluate when FCW alerts occurred. As such, SV- anti-alias filtering, and digitizing. Amplifier gains to-POV collisions were not expected.