The National Highway Traffic Safety Administration is about to publish proposed revisions to its current air brake regulations, but those rules will most likely be less sweeping than some industry people expected
and will not give the anticipated boost to air disc brakes that some had hoped for.
A NHTSA engineer close to the rule writing says the proposals will shorten current stopping limits for heavy trucks by about 30 percent, as observers had predicted. That would reduce the present limit of 355 feet at 60 miles per hour to 248.5 feet at the same speed, for example. This would bring heavy trucks much closer to the performance of smaller, lighter vehicles, which must halt after about 200 feet.
The 30 percent figure would affect a range of trucks at various speeds, but some "oddball" rigs, like car carriers, would have required performance spelled out in distances, said the source, who wished to remain anonymous.
But for now, the new regs will not require specified performance at higher speeds, he said. The industry had expected that stopping requirements would go up to 75 mph, where many rigs now legally travel, especially in some western states. Air disc brakes would be the only way to meet such requirements, and lack of them will mean "high-performance" S-cam drum brakes will still be adequate to meet federal rules.
Stronger front suspensions might be needed to absorb higher dynamic forces seen during such quick stops, but this will require re-engineering of key parts rather than simply adding higher-capacity springs and axles, say suppliers. Beefier components alone would result in a harsh ride that most drivers and owners would not accept. Re-engineered front ends are already in use in Europe.
NHTSA will describe the stopping rule changes in a Notice of Proposed Rule Making, to be published soon. The proposals will formally affect Federal Motor Vehicle Safety Standard 121, the air-brake standard that all vehicle builders must meet. The changes will be subject to comments by the trucking industry, and are not likely to take effect for two or so years.
NHTSA has been slow to rewrite "121" because it realizes that truck builders' engineers have their hands full in preparing for stricter federal exhaust emissions limits in 2007, and then again in 2010. The ‘10 diesel emissions limits and the work of manufacturers to meet them are why the agency is reluctant to specify high-speed stopping performance, the engineer said.
Changes to 121 will also not include electronically controlled braking systems, which some manufacturers have been pushing for. The current standard does not outlaw ECBS, but requires dual air circuits for fail-safe protection; this makes ECBS overly redundant and too costly to be practical. NHSTA is wary of allowing use of a new technology that might not work well with the many old trailers still on the road, the engineer explained.