Truck brakes don't fail by themselves
July 10, 2012
Over the past week, two trucks crashed as a result of their inability to stop on hills. In both cases, the mainstream media reported that the trucks' brakes had failed. That illustrates what the mainstream media knows about truck brakes.
Two well-publicized truck crashes, just a few days apart and both in the Akron area of Ohio, are being blamed on brake failures. Initial reports in the media say that the trucks' brakes 'failed', allowing them to careen out of control down hills.
In the first case,
driver Christopher Burgess steered his out-of-control truck through a shopping plaza and across a city street before driving over an embankment into the Cuyahoga River. Police say Burgess died when his truck struck a tree before overturning and sliding into the river. Burgess is being hailed as a hero for not striking anyone on his high-speed ride through town. Residents say Burgess gave his own life while insuring no one else was hurt in the crash.
Police are investigating the crash to determine if and why the truck's brakes failed allowing it to careen out of control through town.
In the other incident,
which was captured on a gas station security camera, a truck exiting I-77 south at Waterloo Road careened down the ramp and attempted to make a left turn onto Waterloo Rd. The truck appears to run through a red light at the intersection before overturning during the maneuver and coming to rest on its side in front of the gas station.
The driver, Elvis Reyes Barcelo of Houston, Texas, told police at the scene his cargo shifted as he tried to turn left, causing the truck to roll over. Armchair Quarterbacking
In my experience writing about truck brakes for the past 12 years and having driven air-brake equipped trucks for 20 years prior, truck brakes don't fail. They can malfunction, or heat up and cease to work properly, but to imply the brakes failed is an inaccurate summation of the problem.
Were there to be some interruption to the truck's air supply, the spring brakes would apply, providing some stopping force -- about the equivalent to 60-psi brake application. That would certainly be enough to stop the truck under normal conditions, assuming the brake system was in good working order.
Had the brakes become overheated due to dragging or prolonged application, they would be in less than optimum condition, and because of the expansion of the brake drums because of heat, adjustment would be extended to or perhaps past the maximum brake stroke length. Brakes stroking beyond their adjustment limit become dramatically less efficient, thus reducing stopping power.
If the brakes were beyond their adjustment limits to begin with, hard application would heat the brake, causing the drum to expand and rendering them even less effective.
Or perhaps the automatic brake adjusters had been manually adjusted too often, and the mechanism was simply unable to maintain proper adjustment. That type of brake malfunction is well documented in a National Transportation Safety Board report
on a collision between a dump truck and four passenger cars in Glen Rock, Pennsylvania in 2003.
There, investigators found that a mechanic had manually adjusted the automatic brakes adjusters so many times that the clutch mechanism had worn out, causing the automatic adjuster to 'unadjust' each time the brakes were applied. When the driver descended a hill and made multiple brake applications, he unadjusted the brakes to beyond their effective stroke limit, leaving him bereft of braking force.
I'm not saying that's what happened in either of these crashes, but it seems like a possible cause in the case of the dump truck.
As for the crash at the gas station, judging by the speed at which the truck comes down the freeway off ramp in the video, I say it's likely he didn't plan his stop soon enough and rolled over while trying to turn at too high a speed. That his load shifted during the maneuver isn't surprising, but that would have happened as a consequence of the high-speed turn. It likely wasn't the primary cause of the event.We'll Never Know
We will probably not hear anything further about either of these crashes because they were relatively minor in nature. The media rarely follows up on such stories, and police seldom release investigation details to third parties. Unlike airplane crashes where there is always an investigation, these routine type of crashes are investigated and reports filed, but that's about as far as it goes.
It's too bad, because a lot can be learned from crash investigations, and the results can be very instructive. I thought it was interesting that the NTSB investigated the Glen Rock crash, but they had a situation on their hands with poor understanding of automatic brake adjusters, which is a well-known problem that gets very little publicity. Thus, I think the Board wanted to make an example of that crash as lesson to industry in brake maintenance.
There could well have been a mechanical problem with the above-mentioned dump truck crash, but I doubt it was simply a failure of the brake system. In the gas station crash, it looks to me like a case of bad judgment on the driver's part, or perhaps a brake adjustment issue.
Author: Jim Park | Posted @ Tuesday, July 10, 2012 11:54 PM