The National Highway Traffic Safety Administration (NHTSA) has published in the Federal Register a notice of proposed rulemaking to amend its air-brake standard to reduce the stopping distance of truck tractors by 20% to 30%.
NHTSA has "tentatively concluded that truck tractors are capable of achieving a reduction in stopping distance within this range with existing technologies," and many in the industry believe the overall financial impact will be minimal. In the notice, RIN 2127-AJ37, NHTSA says it also will discuss research and request comment concerning improving the braking performance of other types of heavy vehicles (trailers, straight trucks, and buses). NHTSA says it may address improved braking performance for these other vehicles in a future rulemaking.
Comments are to be submitted early enough to ensure that Docket Management receives them not later than April 14, 2006.
On March 10, 1995, NHTSA published three final rules as a part of a comprehensive effort to improve the braking ability of medium and heavy vehicles (60 FR 13216 and 60 FR 13287). The major focus of that effort was to improve the directional stability and control of heavy vehicles during braking through antilock brake system (ABS) requirements. However, the 1995 effort also reinstated stopping distance requirements for air-braked vehicles, and established different stopping distances for different types of heavy vehicles. Previous stopping distance requirements for medium and heavy vehicles had been invalidated in 1978 by the United States Court of Appeals for the 9th Circuit because of issues with the reliability of ABS then in use.
The current stopping distance requirements under Federal Motor Vehicle Safety Standard No. 121, Air brake systems, as established under the 1995 final rule, are determined according to vehicle type. Under the loaded-60-mph stopping distance requirements of FMVSS No. 121, air-braked buses must comply with a stopping distance of 280 feet, air-braked single-unit trucks must comply with a stopping distance of 310 feet, and air-braked truck tractors must comply with a stopping distance requirement of 355 feet. Under the unloaded-60-mph stopping distance requirements of FMVSS No. 121, air-braked buses must comply with a stopping distance of 280 feet, and air-braked single-unit trucks and air-braked truck tractors must comply with a stopping distance requirement of 335 feet. Under the emergency brake-60 mph stopping distance requirements of FMVSS No. 121, air-braked buses and air-braked single-unit trucks must comply with a stopping distance of 613 feet, and air-braked truck tractors must comply with a stopping distance requirement of 720 feet.
For heavy truck tractors (tractors), the current stopping distance test at GVWR is conducted with the tractor coupled to an un-braked control trailer, with weight placed over the fifth wheel of the tractor, and a 4,500-pound load on the single axle of the trailer. This test method isolates the braking performance of the tractor so that only the performance of the tractor is evaluated. The performance of a tractor in an FMVSS No. 121 stopping distance test does not directly reflect the on-road performance of a tractor semi-trailer combination vehicle that has braking at all wheel positions.
Vehicles are tested at lightly loaded vehicle weight (LLVW). Emergency brake system performance is tested with a single failure in the service brake system of a part designed to contain compressed air or brake fluid.
Since the agency established the stability control and stopping distance requirements for heavy vehicles almost ten years ago, data indicate that the involvement of large trucks in fatal and injury producing crashes has slightly declined while vehicle-miles-traveled (VMT) has increased. However, because the number of registered large trucks has increased, the total number of crashes remains high. In 2002, 434,000 large trucks were involved in traffic crashes in the U.S.; 4,542 large trucks were involved in fatal crashes, resulting in 4,897 fatalities (11 percent of all highway fatalities reported in 2002). Seventy-nine percent of the fatalities were occupants of another vehicle, 14 percent were truck occupants, and 7 percent were non-occupants.