Motorcycle

Summary

This is an example of a collision between a motor cycle and a motor car – vehicles of widely differing mass.

Circumstances

A 999cc motorcycle collided with the rear of a stationary motorcar. The rider of the motorcycle, who was not injured, admitted that he collided with the rear of the car but stated that it was at a low speed. The motorcycle fell on its side after the collision. Two occupants in the car claimed injury as a result of the collision.

Investigation

A thorough inspection of the car failed to discover any damage or marks that could be attributed to the collision although it was accepted that the rear bumper could have been replaced prior to the examination. A thorough inspection of the motorcycle revealed scratching to various parts consistent with the motorcycle falling over. Also, there was a flat-spot on the front tyre that was consistent with skidding under heavy braking described by the rider just before the impact.

The mass of the motorcycle and its rider was approximately 274 kg. The kerbside mass of the car was approximately 1580 kg. The car has nearly six times the mass of the motorcycle.

The collision force experienced by the car would have been equal in magnitude but opposite in direction to the collision force experienced by the motorcycle. This is in agreement with Newton’s Third Law.

However, the effect of the collision forces in terms of the acceleration/deceleration and change in speed of each vehicle would have been inversely proportional to the mass of each vehicle. This means that the change in speed of the motorcycle as a result of the collision would have been about six times the change in speed of the car. This is in agreement with Newton’s Second Law.

The widely argued threshold for whiplash injury is a change in speed of 5 mph to the struck vehicle. To cause such a change in speed, the motorcycle would have to strike the rear of the car at about 30 mph. At this impact speed there would have been significant damage to the rear of the car and to the motorcycle. Also, it is highly likely that the rider of the motor cycle would have been injured at this impact speed.

The conclusions of this investigation were that the collision probably took place at no more than 5 mph and that it was highly unlikely that occupants in the car would have been injured as a result of the collision.

Judgement

• The claims for personal injury were dismissed.
• The Claimants were ordered to pay 90% of the Defendant’s costs.
• The Defendant was ordered to pay for the cost of a new rear bumper for the Claimant’s vehicle.

In his summing up the Judge stated:

“The expert from GBB and his report impressed me. The report was thoughtful, carefully researched and the findings were based on careful investigation and clear photographs are evidence of that. All in all I find that his evidence is credible, believable, well thought out, well presented and acceptable to me.”