Federal Motor Vehicle Safety Standards: Heavy Vehicle Antilock Brake System (ABS) Performance Requirement

In March 1995, NHTSA published a final rule amending the hydraulic and air brake standards to require medium and heavy vehicles (e.g., truck tractors, trailers, single unit trucks, and buses) to be equipped with antilock brake systems (ABS) to improve the directional stability and control of these vehicles during braking. We supplemented the ABS requirements for truck tractors with a braking-in-a-curve performance test. The braking-in-a-curve test was not applied to single-unit trucks or buses or to air-braked trailers because we had performed only limited testing of ABS-equipped single-unit vehicles. We stated that we would continue research on dynamic performance tests for single-unit trucks, buses, and trailers, and would consider applying performance test requirements to these vehicles in the future. After issuing the final rule, we tested several ABS-equipped single-unit trucks and buses equipped with both hydraulic and air brakes. Our testing and research indicated that the braking-in-a-curve performance test requirement is practicable for those vehicles. Accordingly, in December 1999, we proposed applying the braking-in-a- curve requirements to them to complement both the ABS equipment requirements and stopping distance requirements. This final rule extends application of the braking-in-a-curve dynamic performance test requirement to single-unit trucks and buses that are required to be equipped with ABS.