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Large trucks and tractor-trailers with ABS anti-lock brakes involved in crashes and accidents have complex systems that must be identified and accounted for in reconstruction and causation issues. Misconception as to skid marks at scenes of crashes can be attributed to the truck/tractor-trailer involved by the police or the investigating agency. Upon investigation and inspection of truck/tractor-trailer it should be noted if the unit has ABS anti-lock brakes and if the system is working. This could change the investigation and reconstruction dramatically as to stopping distance and actions of trucks. ABS systems can apply and release the brakes 5 times a second to keep wheels from locking up and skidding. Numerous times skid marks are attributed to units that did not lock the brakes or skid the tires. Compatibility is also an issue as older trucks pull newer trailers and newer trucks pull older trailers. This creates different issues for reconstruction. Load conditions, total weight, weather, environment, road and tire conditions, brake system maintenance, adjustment, capacity and capabilities must also be considered. These issues can produce conflicting data, cloud issues and render unfair judgments on the drivers/vehicles involved. Remember that since March 1999 trucks and buses with hydraulic brakes are ABS equipped and trucks with air brakes have ABS after March 1997 and air brake trailers have ABS after March 1, 1998. These are manufacture dates of the vehicles. Analyze all data carefully, identify systems properly to understand actions of the vehicles involved in the crash.
* The importance of checking proper operation of the ABS system is that some fleets do not have in house maintenance that can diagnose and repair systems and over the road trucking companies tend to not take trucks/trailers out of service for repair for ABS light that stays on. Bulbs or fuses sometimes disappear from the dash warning light and system. Some veteran drivers remember the late 1970's and don't care for ABS because they think they have more skill in braking than ABS. This is not true as the new ABS systems have proven there reliability. Trucks/trailers with ABS problems will revert back to regular braking if any faults exist and the wheel or axle with a problem can skid. This can change or explain a stray skid mark that shows up at a scene. Other problems can develop with ABS with maintenance or lack thereof ABS wheel sensors, wiring, or exciter tone rings can be damaged and cause faults. Some fleets will avoid the costs as the truck still has regular brakes. Most normal stops by trucks/trailers do not involve ABS functions as ABS only releases the brake when skids/lock-up situations are detected but emergency/panic stops involving crash situations need the ABS functions to stop sooner or maneuver. If you encounter the unusual check for proper ABS functions.
* Author's Note: You are welcome to post this article on any cooperating website, or in any print media,although we request that you include a link to e-mail address at bottom of page and writers credit.
* Published at The ARC Network www.accidentreconstruction.com newsletter March 25,2003 Vol.V,Issue 3
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