Grading and Excavation Contractor

By Daniel C. Brown

Last December, the National Highway Traffic Safety Administration (NHTSA) touched off a debate when it announced a new rule proposing to reduce the required stopping distance of truck tractors by 20% to 30%.

By April, industry manufacturers and others had commented on the proposal. The resulting debate—and final rule—promises to point the direction of future brake technology in on-highway truck tractors. To the extent that single-unit construction trucks often follow on-highway technology, it is instructive to consider who’s saying what about this issue.

Some in the industry, such as brake manufacturer Meritor WABCO, contend that the new rule will be anticlimactic, because few significant changes will be required to achieve the proposed 20% to 30% reduction in stopping distance. At the center of the debate is today’s technology—pneumatically based drum brakes combined with ABS (anti-lock brake system).

“Before the rule came out, the manufacturers weren’t sure whether they would have to migrate to air disc brake technology, and now it appears they won’t have to,” says Robert Braswell, technical director for the Technology & Maintenance Council, a unit of the American Trucking Associations. “It may be necessary to increase the size of the drum, or otherwise enhance current technology, but by and large we should be able to use the basic technology on the trucks.”

Also at issue is the amount and cost of brake testing that the truck manufacturers must do to gain compliance with the new rule. “When you have to do all the testing, that can be more expensive than the actual hardware,” says Mike Kastner, director of government relations for the National Truck Equipment Association (NTEA). “Ultimately you have to do detailed tests on roads with certain coefficients of friction, loaded and unloaded trucks, and all that.” NTEA represents distributors and manufacturers of work-related trucks, truck bodies, and equipment.

Supporting Disc Brakes
A group called Advocates for Highway and Auto Safety, on the other hand, supports equipping new vehicles with all-disc brakes, not just hybrid disc-and-drum systems. “NHTSA recognizes that, despite the adoption of anti-lock brake systems, the current maximum stopping distances of [the current rule] are not particularly stringent,” says Advocates, which is an alliance of consumer, health, and safety groups and insurance companies and agents. Advocates’ comments were contained in a letter to NHTSA from Gerald A. Donaldson, senior research director.

This literally develops into a debate over stopping distances. Advocates says that NHTSA’s test data show that with disc brakes in all wheel positions, one of two loaded test vehicles was able to meet a 30% stopping distance reduction—that is, about 249 feet, as compared with the maximum compliance distance of 335 feet in the current standard. Also, this loaded vehicle was able to exceed a 20% reduction in stopping distance, about 284 feet, using two different hybrid foundation braking designs, one using larger capacity drum brakes on the steering axle with standard size drums on the drive axles—and the other using air disc brakes on the steer axle with standard drums on the drive axle.

Advocates notes that “neither hybrid systems [in tests] achieved even shorter stopping distances of the all-disc configuration [with discs on both steering and drive axles], where the first test truck stopped in distances as short as 218 to 228 feet.” In general, Advocates says, the two GVWR test trucks achieved the shortest stopping distances with disc brakes, averaging 247 feet for the first truck and 241 feet for the second truck.

“This makes it evident that in [NHTSA’s] tests, clear superiority in shorter stopping distances was achieved by all-disc systems over a variety of drum-disc combination systems for foundation brakes,” says Advocates.

Advocates points out that braking efficiency reduction or even failure from overheated drum brakes on large trucks is common. Indeed, thousands of escape ramps have been built in almost all states in the US to provide drivers of runaway trucks with a means to decelerate into an upgrade ramp with an impact attenuation installation.

The Advocates group supports a 30% reduction standard through the use of disc brake systems—despite the added initial costs in equipping new tractors with all-disc systems. In actual service conditions, “there is little question that disc brakes will outperform both hybrid and all-drum foundation brake systems,” writes Advocates’ Donaldson.

Future Direction
Some form of electronic control will be included in future North American brake systems, says Meritor WABCO’s chief engineer Alan Korn in his comments to NHTSA. But moving to disc brakes and electronically controlled braking systems (ECBS) would be a complete departure from the current system of ABS and drum brakes. In an interview with Fleet Owner, a trucking publication, Korn said, “The reason for not jumping from one technology to another right now is that many heavy truck safety features, from traction control to rollover prevention, can now be enabled with ABS.”

Meritor WABCO, however, opens the door to electronically controlled brakes by recommending that NHTSA begin a review of the current stopping distance standards “outside of this notice and consider the regulatory ramifications necessary to allow optional use of ECBS in the future.”

Daniel C. Brown is the owner of TechniComm, a communications business based in Des Plaines, IL.

GEC - July/August 2006

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