Summary

This is an example of a high-value claim involving a collision between a Leyland Tiger coach and a Toyota Celica. It shows how research and analysis can be instrumental in establishing the truth.

Circumstances

The Toyota was travelling in front of the coach when it braked suddenly as a pedestrian stepped out onto a
crossing. The coach was unable to stop and it struck the rear of the Toyota.

coach image

The coach was carrying passengers travelling to a wedding. A majority of the passengers claimed personal injury.

GBB was asked to comment upon the likely speed of impact and the effect of the collision upon the occupants of the coach

Investigation

An examination of the tachograph chart showed that the coach was travelling at 18.6 mph (8.31 m/s) at
the moment of impact. A momentum calculation was then carried out to determine the final speed, the acceleration and the average collision force experienced by each vehicle.

The final speed of each vehicle was calculated as follows:

Mass ratio of the vehicles: Coefficient of restitution: r = 0.2
(This takes into account the balance between elastic and inelastic
deformation)

Initial velocity of the coach: U1 = 18.6 mph (8.31m/s)

Final velocity of the coach: 16.8 mph or 7.51 m/s

Final velocity of the car: mph or 9.18 m/s

Change in speed of the coach: Δv = 8.31 – 7.51 = 0.8 m/s (Deceleration)

Change in speed of the car: Δv = 9.81 – 0 = 9.81 m/s

The average acceleration of each vehicle as a result of the
collision can be calculated from: a= where Δt is the collision time of around 0.2 sec.

Average acceleration of the coach = -0.8/0.2 = -4.0 m/s2 or 0.41g.
Average acceleration of the car = 9.18/0.2 = 45.9 m/s2 or 4.68g.

From this it can be seen that the magnitude of acceleration experienced by the car was much larger than that of the coach. This is due to the large difference in mass between the vehicles.

The average collision force can now be calculated from the equation resulting from Newton’s second law: F = ma

Average collision force acting on the coach = 14620 x -4.0 = -58,500 N
Average collision force acting on the car = 1275 x 45.9 = 58,500 N

This shows that the average force experienced by the car is equal in magnitude but opposite in direction to that experienced by the bus despite the large difference in the mass of each vehicle. This is in complete agreement with Newton’s 3rd Law.

Bus testing research carried out by GBB shows that the value of deceleration experienced by the coach is similar to that which would occur under emergency braking.

The graph below shows the deceleration of a bus under emergency braking along with the deceleration of a striking vehicle from one of the full-size crash carried out by GBB.

coach graph image

It can be seen that the deceleration experienced by the striking vehicle in Crash Test 2 (blue line) is much greater than that experienced by the bus (black line) during emergency braking.

From this it was inferred that since the occupant of the striking vehicle in Crash Test 2 was not injured, then it was considered to be highly unlikely that occupants in the coach involved in this collision would have been injured. Other evidence was also considered by the court which resulted in the following judgement.

Judgement

Twenty claimants had their cases dismissed. Another four claimants persisted but were forced to drop their claims on the second day of the trial at Manchester County Court. The claimants were ordered to pay £25,000 costs and their file was passed to the Director of Public Prosecutions and Greater Manchester Police with a view to possible proceedings regarding fraud. Subsequently 4 of the individuals involved have been sentenced.

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