A “Toolbox” for Forensic Engineers

Component Failure in Road Traffic Accidents 343
Figure 10.21 Witness marks (arrows) from the lock washer on the underside
of the bolt head.
had been solely side-to-side slewing when the bolts finally pulled out, this
would not account for the way the plate itself and one of the side links had
buckled, nor for the bending of both bolts in the same direction just under
their heads. Many other Landrover vehicles (including those operated by the
same police force for recovery purposes) were fitted with this same type of
towing bracket and no similar failure had ever been encountered. He considered
this damage could only be accounted for if the front corner of the
trailer had been pushed back violently while still coupled to the towing vehicle
and reasonably in line with the direction of travel.
This was the view accepted in the subsequent litigation between the
insurance companies, where the major issue was whether or not the trailer
had detached before the collision and had veered across the road into the
path of oncoming traffic. It was agreed that because the trailer was 40 cm
wider than the towing vehicle the front corner would have been projecting
almost to the middle of what was a fairly narrow main road. The oncoming
car was traveling fast and its front wheel collided with the corner of the trailer,
pushing it back violently and tearing the tow ball plate off the bracket. This
accounts for the buckling of the left side arm and why both bolts bent in the
same direction as they ripped threads of the nuts retaining the towball. The
collision forces must have been greater than any previously applied up to
that moment of impact. The damage to the car was all along its offside, none
near the center of the hood as would have occurred in a frontal collision.
Loose scaffolding on the trailer had been projected through the windshield
on the driver’s side only. The offside wheel of the trailer had been torn from
its axle but there was no significant damage to the tow hitch still attached at
the front.