A rear-end collision (often called simply rear-end or in the UK a shunt) is a traffic accident wherein a vehicle (usually an automobile or a truck) crashes into the vehicle in front of it. Common factors that contribute to rear-end collisions include by driver inattention or distraction, tailgating, panic stops, and reduced traction due to weather or worn pavement. It may also be a rail accident wherein a train runs into the rear of a preceding train.
Typical scenarios for rear-ends are a sudden deceleration by the first car (for example, to avoid someone crossing the street) so that the car behind does not have the time to brake and collides with the first. Alternatively the following car may accelerate more rapidly than the leading (for example, leaving an intersection) resulting in a collision.
As a rule of thumb, if the two vehicles have similar physical structure, crashing into another car is equivalent to crashing into a rigid surface (like a wall) at half of the closing speed. This means that rear-ending a stationary car while travelling at 50 km/h (30 mph) is equivalent, in terms of deceleration, to crashing into a wall at 25 km/h (15 mph). The same is true for the vehicle crashed into. However, if one of the vehicles is significantly more rigid (e.g. the rear of a truck) then the deceleration is more typically reflected by the full closing speed for the less rigid vehicle.
A typical medical consequence of rear-ends, even in case of collisions at moderate speed, is whiplash. In more severe cases permanent injuries, e.g. herniation, may occur. The rearmost passengers in minivans benefit little from the short rear crumple zone, so they are more likely to be injured or killed in a rear-end collision.
For purposes of insurance and policing, the driver of the car that rear-ends the other car is almost always considered to be at fault due to not leaving enough stopping distance or lack of attention. An exception to this rule comes into play if the rear-ended vehicle is in reverse gear. If the driver of the car that was rear-ended files a claim against the driver who hit him, said driver could be responsible for all damages to the other driver's car. According to data reported by the NHTSA, the percentage of rear end accidents to all crashes is between 23–30%.
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