The Crash Avoidance group at NHTSA VRTC is currently conducting research and vehicle testing to examine issues relating to passenger vehicle brake systems. Research focuses on the areas listed below.

Light Vehicle Antilock Brake Systems (ABS) Research Program

Light Vehicle Antilock Brake Systems (ABS) Performance Test Development
  • NHTSA's most recent notice on ABS, ANPRM; Deferral of Rulemaking (61 FR page 36698), announced that the Agency was deferring a decision to mandate antilock brake systems (ABS) for vehicles with a gross vehicle weight rating (GVWR) of 10,000 pounds or less. This was done because the real world crash avoidance performance of these systems appears to be below expectations. However, even though the Agency does not require ABS on light vehicles, light vehicle manufacturers are currently voluntarily equipping a large percentage (approximately 55 percent) of new light vehicles with ABS.

    Currently, the Agency’s harmonized light duty brake system standard, FMVSS 135, does not contain either test procedures or performance requirements for ABS. Although the Agency is not considering mandating ABS at this time, the Office of Crash Avoidance Standards (OCAS) believes the Agency should develop test procedures and performance requirements for ABS equipped light vehicles.

    The Agency evaluated the ECE Regulation 13-Harmonized ABS test procedures and requirements by conducting vehicle tests using the R 13-H ABS procedures. NHTSA feels that the coefficient of friction and adhesion utilization procedures need to be improved. Also, there are several portions of the ECE R 13-H ABS procedures that need to be more objectively defined.

    Research was performed to develop a test procedure to measure the braking efficiency of a vehicle with the ABS cycling. Many possible means of measuring braking efficiency were explored.

  • NHTSA Final Report:  "NHTSA Light Vehicle ABS Performance Test Development" DOT 809 747 [PDF 2.5MB]
 Consumer Brake Information Initiative
NHTSA explored the feasibility of developing tests to measure the brake system performance of light vehicles. If viable test protocols could be developed, it would enable NHTSA to provide consumers with valuable crash avoidance safety information, and help drive the market towards improving braking performance. Concerns with developing a brake system performance test focus primarily on questions of variability. The sources of variability include vehicle-to-vehicle differences that exist for a given make/model due to (possibly) different standard tires or vehicle options, lining-to-lining differences in the performance of brake linings, tire-to-tire differences in the frictional performance of tires, differences in test conditions (temperature, humidity, etc.), changes in the frictional characteristics of test surfaces due either to differences in test conditions, the passage of time, or from site-to-site, and the effects of using different drivers to perform the tests.

Work was performed to determine the level of variability in stopping distance tests of light vehicles that is due to differences between drivers. 648 stopping distance tests were conducted with three expert drivers in three different cars on wet and dry asphalt with the ABS working and disabled. The results of this research are contained in the report "Brake Test Methodology Study - Driver Effects Testing" (see below).

Brake Testing Methodology Study - Driver Effects Testing: NHTSA explored the feasibility of developing brake tests to measure brake system performance of light vehicles. Developing test procedures requires controlling test variability so that measured differences between vehicles are more than just experimental noise. Possible sources of uncontrolled variability include environmental conditions, vehicle-to-vehicle differences for a given model, brake system changes with time, test driver differences, test surface friction changes with time, and test surface friction differences between test sites. The objective of this project was to determine the level of variability in stopping distance tests of light vehicles that is due to differences between drivers. 648 stopping distance tests were conducted with three expert drivers in three different cars on wet and dry asphalt with the ABS working and disabled. All four independent factors had a statistically significant effect on the stopping distance. Several interactions of the independent variables were also significant. The largest main effect was the differences between vehicles. The effect of ABS and surface condition and drivers were all fairly small. The interaction between ABS condition and surface was also small but indicated that ABS mattered more on the wet surface. The remaining interactions were also fairly small. In conclusion, this test procedure measured differences between all three vehicles with very high statistical certainty. Unfortunately, this test procedure used a large number of replications and drivers. If the goal for a brake test program is only to distinguish large differences in braking performance, fewer replications and drivers would be needed for each vehicle tested.