Of discs and drums

When the National Highway Traffic Safety Administration (NHTSA) proposed to cut the stopping distance for heavy-duty trucks by 20% to 30% last December, trucking applauded the rulemaking as a step in the right direction. What pleased people most was that NHTSA's data suggested that carriers could be in compliance by using larger brakes at a cost of about $150 per tractor for drums and $1,300 for discs

When the National Highway Traffic Safety Administration (NHTSA) proposed to cut the stopping distance for heavy-duty trucks by 20% to 30% last December, trucking applauded the rulemaking as a step in the right direction. What pleased people most was that NHTSA's data suggested that carriers could be in compliance by using larger brakes at a cost of about $150 per tractor for drums and $1,300 for discs to achieve a 30% reduction in stopping distance, and about $100 and $900, respectively, to achieve a 20% reduction.

With two years of lead time after a final decision, many believe the rulemaking is not only reasonable but, if NHTSA's estimates are correct, carriers would see financial gains because of fewer crashes and the property damage they entail.

A 30% improvement in brake performance could prevent 257 fatalities and 284 injuries, NHTSA noted. A 20% improvement could save 104 lives and prevent 120 injuries. “… the agency believes that $166 million and $32 million of property damage would be prevented with the proposed 30 percent and 20 percent reduction in stopping distance, respectively,” the proposal noted.

As with many proposed rulemakings, however, it could have further ramifications.

One group closely watching the proceedings is the Commercial Vehicle Safety Alliance, which notes that bad brakes account for about 55% of out-of-service vehicles tested at roadside inspections.

“We would like to see some consistency in brake design,” says Steve Keppler the group's director, policy & programs. If carriers employ many different brake designs to reach compliance, the job of CVSA inspectors will become more difficult.

Keppler would like suppliers to consider ‘inspectability’ when manufacturing larger brakes. Drum brakes are easier to inspect, but inspectors have trouble seeing inside disc brake assemblies. Now, only a small percentage of trucks use discs, but if trucks use discs to reach compliance, then there might be a problem. “If we can't see it, we can't inspect it,” he says.

“On some vehicles, it might be difficult to reach 30% without discs,” suggests Richard Radlinski, who worked at NHTSA for 25 years and is now a consultant based in Queenstown, MD. In particular, 4 × 2 tractors transfer a great deal of weight to the front axle and may be good candidates for disc brakes.

Radlinski notes that using larger drum brakes may not be as easy as it first appears. As they get larger, slight manufacturing or mounting differences can be exacerbated and the truck could pull to one side without a near perfect match.

Some truck makers may choose instead to reach compliance by reducing the gross axle weight ratio to even out the weight burden. This may be a viable strategy for tractor-trailers, but “it will be much more difficult to shorten the stopping distance on trucks,” Radlinski says.

Radlinski notes that if more trucks move toward disc brakes, which NHTSA suggested might become more common, then states will have to rely more on performance-based brake testers because inspectors have trouble eyeballing the disc brakes.

While not its direct intention, NHTSA's rulemaking could help push truck makers toward disc brakes, which would ultimately lead to performance-based brake testing at roadside inspection.

Moving to performance-based testing would not only solve CVSA's inspectability issue, but prevent contentious “differences of opinion” between drivers and inspectors and a fairer shake for everyone involved.

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