A derailment is when a train runs off its rail, either because of a collision with another object, a conductor error, mechanical track failure, broken rails, or defective wheels. A derailment doesn't necessarily mean the train leaves the tracks – some may be minor.

Why do most trains derail?

Note that broken rails and welds are responsible for more than half of all track-related derailments. The second most common caused of train derailments is equipment failure in a train or car. This can include train breaks failing, a locomotive bearing or wheel failure, or electric defects in the locomotive.

How likely is it for a train to derail?

Train Accident Facts and Figures

About every hour and a half a train collides with another object or is derailed. Every two weeks a train that is carrying hazardous materials derails in the United States.