A: For lower speed inline rear end impacts one would expect structural restitution to play a part since it acts to increase the speed of the struck vehicle while reducing the speed of the striking vehicle.
And to add to that generalized speed difference driver actions subsequent to the collision might tend to increase the relative speeds
- if for example the striking vehicle driver was braking and continued to brake subsequent to the collision.
Also if the struck vehicle driver is knocked off the brakes as a result of the collision and so the vehicle would roll freely.
- For example, if the impact speed produces sufficient damage to the rear of the struck vehicle such that the drag on the struck vehicle is similar to braking (rear wheels impaired or locked due to the collision) that would reduce the separation velocity and therefore the vehicle might travel together to positions of rest.
Alternatively if the speeds/vehicle types caused a drag on the struck vehicle due to impairment of the rotation of the wheels due to damage that would appear as a greater difference in the separation speeds.
Under-ride and over-ride of the bumpers which may not lock however which might reduce the amount of relative separation velocities of the vehicles.
- "Effects of Restitution in the Application of Crush Coefficients", SAE Technical Paper No. 970960