derailment

Derailment is the event in which a rail vehicle, typically a locomotive or car, leaves its tracks. It is most commonly associated with rail transportation, but the term can also refer to other wheeled vehicles. A derailment often disrupts service and can lead to damage, injury, or environmental harm.

In rail systems, derailments occur when wheel-rail contact can no longer guide the vehicle along the intended path. This can result from wheel climb, where a wheel lifts over the rail, or flange climb, where the wheel flange rides up the rail and leaves the track. Speed, loading, track geometry, rail condition, and the presence of obstacles or misaligned switches all influence the likelihood of a derailment.

Common causes include track defects such as gauge variation, improper alignment, or worn or damaged rails; excessive or concentrated loads; defective wheels or axles, such as out-of-round wheels or flat spots; faulty switches or turnout geometry; and collisions with objects or other vehicles. Human error and adverse natural conditions, such as landslides or earthquakes, may also contribute.

Derailments can be partial, involving only one wheelset leaving the rail, or complete, with a full car or locomotive departing the track. High-speed derailments tend to cause greater damage, including overturns.

Prevention focuses on maintaining track geometry and surface condition, enforcing appropriate speed restrictions, ensuring wheel and axle integrity, and using derailment protection devices where appropriate. Timely inspections, reliable switches, proper loading practices, and corrective maintenance reduce derailment risk and mitigate consequences when derailments do occur.