New thinking on faster braking

Truck drivers in 2002 led all occupations in the United States in total number of illnesses and injuries with 112,000 requiring days away from work, according to a report issued by the Bureau of Labor Statistics in late March. Truck drivers also led in median days away from work at 13 with more than a third of those drivers away from work 31 days or more. Not surprisingly given truck driver demographics, 93 percent of those injured or sick were men. Half of their injuries were sprains or strains – often to the trunk or lower extremities – stemming from falls, overexertion or contact with objects and equipment. A copy of the full report is available at this site.

Occupational Safety and Health Administration said its site-specific targeting (SST) plan for 2004 will focus on about 4,000 high-hazard worksites for unannounced comprehensive safety and health inspections. The agency surveyed about 80,000 employers, including those in trucking, to obtain injury and illness numbers for 2002. The SST program will initially cover about 4,000 worksites that reported 15 or more injuries or illnesses that resulted in lost work days, restricted work or transfer for every 100 full-time workers. Sites that had 10 or more cases of days away from work per 100 full-time workers also are on the primary list. OSHA’s SST plan is available at this site.

Federal Motor Carrier Safety Administration has denied 17 applications from individuals who requested an exemption from the federal diabetes standards applicable to interstate truck drivers. Six applicants did not have three years’ experience driving a CMV on public highways with insulin-treated diabetes mellitus. Four lacked sufficient recent driving experience to predict future performance. The remaining seven applicants were denied exemptions for various reasons. A notice of the denials and reasons for them was published in the March 25 Federal Register.

Ryder System has launched, which provides fleet owners and others access to safety-related products, compliance services, training and information. In addition to tools for ordering products and services online, the site provides access to Ryder’s national listing of safety training schedules, including contact information.

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Interstate school transportation operations by locally governmentally operated educational agencies will remain exempt from the Federal Motor Carrier Safety Regulations (FMCSRs) except for the regulations they currently must follow — commercial driver’s licenses and controlled substance and alcohol testing. Following a public comment period, FMCSA withdrew an advance notice of proposed rulemaking concerning whether to apply FMCSRs to such organizations. (Docket No. 7174)

DriveCam Video Systems has scheduled DriveCam Academy management training courses for June 29 in Los Angeles and Sept. 28 in Chicago. Created for DriveCam customers, the DriveCam Academy is a one day course that provides advanced training on driver improvement and incident prevention using the DriveCam safety program. For more information, contact Del Lisk at [email protected].

It’s conventional wisdom in trucking that air disc brakes offer better performance – at a significantly higher cost. It’s also considered to be a basic truth that air discs on an entire tractor would have to be matched to a disc-braked trailer or suffer frequent maintenance. In the past, both these truths have been all but self-evident.

But now, Bendix Commercial Vehicle Systems is suggesting that we look at things differently. What they have to say puts a new spin on a potential federal standard requiring heavy trucks to go from 60 mph to a full stop in 248 feet (see “More brakes for less money,” Safety, April 2001).

The company has developed a new-generation disc system intended to make discs so desirable from a maintenance perspective that overall cost per mile could drop, as compared with drums. Bendix claims the discs are so good they would even overcome the work and wear imbalance problems of running disc tractors and drum trailers, says Anton Schneider, engineering manager disc brakes at Bendix.

The super discs have been developed for Europe, where air disc brakes on trucks are now the norm. One of the goals of the design was to make basic brake maintenance a simple replacement of linings and rotors. Imagine a system intended to eliminate the total rebuild that maintenance managers must perform on drums to return trucks to service.

And, that’s just what Bendix has accomplished, say Schneider and Ron Plantan, principal engineer. First, the slideability of the calipers has been greatly improved. Says Schneider, “The sliding pins are sealed and lubed for life, giving the caliper a 10- to 15-year life.” Second, the adjustment mechanism is integrated with the caliper rather than a separate mechanism and is lubed for life, he says.

Rotor material and design also have been improved, Schneider says. “We are using a much larger rotor than in the past – 17 inches in diameter rather than 15 inches. The rotor material has been improved to help it handle the energy, and cooling has been improved through better airflow.” Bendix’s double-layer discs have fins driving air through their centers, while drums have “limited air circulation.” Cooling fights heat cracking. Larger friction material elements have been developed in tandem with the other changes. Bendix projects that for on-highway applications pad life could exceed 500,000 miles and rotor life could run 700,000 to 1 million miles. “Looking at overall cost per mile after 3 to 5 years, there could be significant benefits,” Plantan says.

Better heat removal and component durability are keys to making a disc tractor compatible wear-wise with older, drum trailers. Another is hysteresis, the consistency with which brakes apply and release. Bendix says older discs matched well with drums on the apply cycle, but didn’t release as quickly, making for part of the imbalanced wear equation. But Bendix’s new discs are more compatible with drums. A test by Bendix with an all-disc tractor pulling various drum trailers produced a 500,000-mile pad life and 950,000-mile rotor life.

But our biggest concern here is safety, and air discs represent an improvement. The stopping distance relative to drums drops precipitously at higher speeds. For example, in those long downgrades, where truckers normally experience fade, drums, in three succeeding stops from 40, 60 and 75 mph, produced a final stopping distance over 600 feet. Under the same conditions, air discs stopped consistently in the 320-foot range.

The improved drum systems to come – producing stopping distances of less than 248 feet from 60 mph – seem adequate until you consider how fast trucks are actually running today. Eighty-four percent of the states have limits of 65 mph and above. “I’ve followed trucks doing 80 mph where the speed limit is 65,” Plantan says. “At that speed, you need very good brakes to stop.” Present drum systems would have a stopping distance of 800 feet or more under severely faded conditions, Plantan says. “What if you have visibility of only 350 to 500 feet – all that headlights provide – in a nighttime situation? At 75 mph, can you see what’s ahead and react in time?”

On long grades or in repeated hard stops, “the Achilles heel of drums” shows up, Plantan suggests. You can run out of stroke. Tests run by Bendix under hot-stop, 40 to 0 conditions used up 99 percent of available stroke.

Add to these possible advantages the fact that drivers like the feel in everyday situations. More consistent response and a passenger car feel, claims Bendix, could leave your drivers grinning.
– John Baxter is CCJ‘s senior associate editor.

Preventable or Not: Tricked by tricked-out cars
John Doe was still sipping coffee as he rolled onto a level, multi-lane, 55-mph limited access surface road and skip shifted up to the speed limit. Conditions were ideal, with sunshine, a dry, straight road and moderate traffic. He popped a tape of country music into his player.

Doe behaved himself as usual, rolling along in the right lane at the posted limit. The next thing that happened posed no trouble. He noticed that he was in an “exit only” lane seeing a sign to that effect. Since he was bound for an exit much farther down the road, he looked in his left side mirror, signaled and safely shifted into the center lane.

Only moments after his lane change, trained to scan his mirrors, Doe glanced in his passenger side West Coast mirror and saw a light blue 1940s Ford street rod rolling at only a mile per hour or two faster than his rig down the exit lane. Since the operator was not signaling or making any other moves, Doe assumed the driver was going to exit.

Without signaling – and some distance before the end of the exit-only lane – the hot rod driver suddenly accelerated until he was just a foot or two past Doe’s front bumper and then cranked his wheel sharply left. He darted across in front of Doe with only inches to spare. Doe’s heart raced, and he reacted by angrily pounding on his steering wheel and cursing at the top of his lungs.

Just as Doe began to thank his lucky stars, a high-speed yellow 1960s GTO briefly showed up in Doe’s peeper window, occupying what little was left of the right lane. Only seconds later, as the exit lane ended, the GTO, eager to continue down the main highway at all costs, cut abruptly in front of Doe without sufficient clearance, striking his front fender on the right side. A few days later, Doe received a warning letter from his safety director charging him with a preventable accident.

Doe felt he had been maligned, and was the victim of a very rare one-two punch no sensible trucker could have anticipated. So, his fair-minded safety director offered to let the National Safety Council’s Accident Review Committee decide who was right. What NSC noticed in reviewing the facts was that while pounding on his doghouse, Doe had neglected to scan his mirrors as drivers always should, delaying his awareness of the presence of the second maniac. The committee decided that just because he had nearly been hit by one wild driver was no reason to believe another might not be right behind, perhaps even chasing his buddy. NSC ruled the accident preventable.