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For the definition of derailment in psychiatry, see thought disorder.

A derailment is an accident on a railway whereby a train leaves the rails, which usually results in damage, injury, and often death.

There are several main causes of derailment: broken or misaligned rails, excessive speed, and faults in the train and its wheels. Derailment can also occur as a secondary effect in the aftermath of a collision between two or more trains. Trap points protect main lines from runaway vehicles by deliberately derailing them to bring them to a stop. Flangeless wheels make it easier for a locomotive to negotiate curves, but make them more prone to derailment.

Contents 1 Rerailing 2 Example accidents 2.1 20th Century 2.2 21st Century 3 See also

Rerailing a train after it has derailed is not an easy task, and often requires the use of large rail mounted cranes.

Most railway accidents involve derailment. See list of rail accidents.

• November 11, 1833 – Hightstown, New Jersey, United States: Carriages of a Camden & Amboy train derail at 25 miles per hour in the New Jersey meadows between Spotswood and Hightstown when an axle breaks on a car due to an overheated journal. One car overturns, killing two and injuring fifteen. Among the survivors is Cornelius Vanderbilt who will later head the New York Central Railroad. He suffers two cracked ribs and a punctured lung, and spends a month recovering from the injuries. Uninjured in the coach ahead is former U.S. President John Quincy Adams, who continues on to the Nation's Capital the next day.

• January 6, 1853 – Andover, Massachusetts, United States: The Boston & Maine noon express, traveling from Boston to Lawrence, Massachusetts, derails at forty miles an hour when an axle breaks at Andover, and the only coach goes down an embankment and breaks in two. Only one is killed, the twelve-year-old son of President-elect Franklin Pierce, but it is initially reported that General Pierce is also a fatality. He was on board but is only badly bruised. The baggage car and the locomotive remain on the track.

• April 16, 1853 – Cheat River, West Virginia, United States: Two Baltimore & Ohio passenger cars tumble down a hundred foot ravine above the Cheat River in West Virginia, west of Cumberland, Maryland, after they are derailed by a loose rail.

• December 12, 1917 – Saint Michel de Maurienne, France: A military train derails at the entrance of the Fréjus Rail Tunnel after running away down a steep gradient; brake power was insufficient for the weight of the train. Around 800 deaths estimated, 540 officially confirmed. The world's worst ever derailment, and worst rail disaster up to the end of the 20th century.

• May 10, 2002 – Potters Bar rail crash, Potters Bar, England, United Kingdom: A points failure caused a British Rail Class 365 to derail on the approach to Potters Bar railway station. As a result, the train slid sideways across the station platform, killing six on the train and one on the platform.
• January 31, 2003 – Waterfall train disaster, Waterfall, New South Wales, Australia: A train derails as it rounds a sharp curve rated for 60 km/h at a speed of 117 km/h, after the train driver has a heart attack. The two safety mechanisms - the driver's deadman's brake which remained depressed because of the drivers weight, and the guard who could have applied the emergency brake, but was in a microsleep at the time - were found to be the direct causes of the incident.
• February 23, 2007 – Grayrigg derailment, Grayrigg, England, United Kingdom: The 17:15 Virgin West Coast Pendolino service from London Euston to Glasgow Central, travelling on the West Coast Main Line derailed for an as yet unknown reason. Initial investigations suggest a points defect.

• List of rail accidents
• Classification of railway accidents