The U.S. Federal Motor Carrier Safety Administration issued a final rule in
August, 2002 that allows inspectors to use roller dynamometers, breakaway
torque testers, and other high-tech devices to check brake compliance on
commercial trucks and buses and issue citations based on the results.
The rule represents the culmination of research that started nearly 10 years ago. It applies to all commercial motor vehicles weighing over 10,000 lb, and was
effective on Feb. 5, 2003.
Performance-based brake testers or PBBTs, as they’re known, measure the brake forces at each individual wheel and are the most practical way to determine
whether a vehicle complies with the actual legal standards for brake performance.
U.S. federal safety regulations require at least 43.5% braking force as a
percentage of actual gross vehicle weight at a speed of 20 miles an hour.
“When was the last time you saw a test for braking force being done at the roadside?” asks Dale Holman, whose Georgetown, Ont., company, Truck Watch Services, operates a mobile PBBT and provides brake training for inspectors, mechanics, and fleet supervisors. “It’s completely impractical. That’s why you have
inspectors crawling around measuring stroke travel. They see it as the best
alternative. Unfortunately, brake adjustment doesn’t tell the whole story about
whether your truck is going to stop when you want it to.”
FMCSA’s new rule addresses specific types of PBBTs, including roller
dynamometers, breakaway torque testers, and flat-plate testers. The agency
stresses that the devices cannot replace an inspector in finding defects unrelated
to immediate brake performance–air leaks, chafed brake hoses, and the like. But PBBT’s can provide an objective and consistent measure of vehicle braking
performance without having to crawl underneath the vehicle. The machine itself is not hard to run, Holman says, but operators do need training to be able to properly interpret the data it can generate.
“It produces a lot of information about your braking system, including
safety-related things that an inspector usually isn’t concerned about or looking for, like brake timing and performance across an axle for balance,” he says. Indeed, in the regulations, balance is not an issue. But the first inspector with a dyno who sees that the first axle is strong on the right, and the rear is strong on the left, is going to question whether the vehicle is safe.
“Your truck may show 45% braking of the gross weight rating, and all the brakes
may be in adjustment. You may have just had a complete brake job done. But it’s
the lining and drum fit that matters most, not the brake stroke,” Holman says.
“Knowing what the machine has told him, do you think an inspector or cop is going to let your truck go back on the highway? Imagine if he lets it go and a mile down the highway it jackknifes and kills someone?”
Enforcement agencies will be able to apply for federal funds to pay for the PBBTs,
which typically cost tens of thousands of dollars. Several states, provinces, and local authorities have experimented with PBBTs as an inspection tool, but the cost has discouraged them from investing in the machines.
The new rule is on the Internet at dms.dot.gov. The docket number is FHWA-1999-6266.