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Truck/Tractor-trailer brakes and accident reconstruction
By Robert Reed
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 diaqnose
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 sometimes disappear from the dash warning
light.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 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.
Truck/Tractor-trailer
brakes and accident reconstruction
by Robert Reed
December 10, 2002
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