derailed

In rail transport, a derailment is a type of train wreck that occurs when a rail vehicle such as a train comes off its rails. Although many derailments are minor, all result in temporary disruption of the proper operation of the railway system and they are a potentially serious hazard.
A derailment of a train can be caused by a collision with another object, an operational error (such as excessive speed through a curve), the mechanical failure of tracks (such as broken rails), or the mechanical failure of the wheels, among other causes. In emergency situations, deliberate derailment with derails or catch points is sometimes used to prevent a more serious accident.

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