The test is now required for tractor ABS systems, but in 1995, when ABS requirements were adopted, NHTSA had done only limited testing of ABS-equipped straight trucks and buses. Tests done since then have confirmed that the braking-in-a-curve performance test is practicable and would complement current ABS equipment and stopping distance requirements, the agency said.
The proposed tests would be similar to those in effect for air-braked tractors, but with slight modifications to allow for vehicle differences and to accommodate vehicle with hydraulic braking systems. Tests would be done on fully loaded and lightly loaded vehicles. A 2-foot-wide road with a 500-foot radius would represent an exit ramp with a moderately sharp curve. A low friction surface would represent wet or worn asphalt. Proposed test speed is 30 mph or 75% of maximum drive-through, whichever is lower. Test vehicles would have to remain within a 12-foot lane during at least three of four consecutive stops.
If the rule is adopted, manufacturers would have two years to comply. For more information see the December 21, 1999, Federal Register, pages 71377-71388. It can be accessed on the Internet at www.access.gpo.