Derailment

A derailment is a disruption of the normal wheel-to-rail relationship, in which one or more wheels leave the rail they are meant to run on. Derailments range widely in severity, from a single wheel on the ground at low speed in a yard to the large pile-ups that make the news, and everything in between.

Causes

Derailments can originate in the track, the equipment, or the way a train is handled. Track-related causes include broken rails, misaligned switches, and geometry defects. Equipment-related causes include defective wheels, broken components, and truck problems. Train-handling causes include excessive in-train forces, such as high buff forces on a curve that can push a car off the rail. Many derailments result from a combination of factors rather than a single cause.

Consequences and Response

Even a minor derailment stops the affected movement and requires the car to be rerailed and inspected before it can continue. More serious derailments can damage track, equipment, and lading, block the line, and in some cases release hazardous materials. Because of these risks, conditions that could lead to a derailment - such as defects found at inspection or in interchange - are taken seriously, and cars with such defects may be set out or refused as a rejection at interchange rather than allowed to continue in service.