Derailment

The train was traveling between Hightstown and Spotswood, New Jersey, and derailed after an axle broke on one of the carriages as a result of a journal box catching fire.

[1] During the 19th century derailments were commonplace, but progressively improved safety measures have resulted in a stable lower level of such incidents.

[3] The mechanism of gauge widening is usually gradual and relatively slow, but if it is undetected, the final failure often takes place under the effect of some additional factor, such as excess speed, poorly maintained running gear on a vehicle, misalignment of rails, and extreme traction effects (such as high propelling forces).

The crabbing effect referred to above is more marked in dry conditions, when the coefficient of friction at the wheel to rail interface is high.

Modern technologies have reduced the incidence of these failures considerably, both by design (specially the elimination of plain bearings) and intervention (non-destructive testing in service).

The vehicle wheelsets become momentarily unloaded vertically so that the guidance required from the flanges or wheel tread contact is inadequate.

If any of these measures are inadequate, the track may buckle; a large lateral distortion takes place, which trains are unable to negotiate.

The first concentration of levers for signals and points brought together for operation was at Bricklayer's Arms Junction in south-east London in the period 1843–1844.

It occasionally happens that a driver incorrectly believes they have authority to proceed over the trap points, or that the signaller improperly gives such permission; this results in derailment.

If a train collides with a massive object, it is clear that derailment of the proper running of vehicle wheels on the track may take place.

Although very large obstructions are imagined, it has been known for a cow straying on to the line to derail a passenger train at speed such as occurred in the Polmont rail accident.

Derailment has also been brought about in situations of war or other conflict, such as during hostility by Native Americans, and more especially during periods when military personnel and materiel was being moved by rail.

Generally this uses compressed air as a control medium, and there is a measurable time lag as the signal (to apply or release brakes) propagates along the train.

The rear part of the train may overrun the front part, and in cases where coupling condition is imperfect, the resultant sudden closing up (an effect referred to as a "run-in") may result in a vehicle in tare condition (an empty freight vehicle) being lifted momentarily, and leaving the track.

This generally arises when a driver fails to slow the train for a sharp curved section in a route that otherwise has higher speed conditions.

The guidance system of practical railway vehicles relies on the steering effect of the conicity of the wheel treads on moderate curves (down to a radius of about 500 m, or about 1,500 feet).

The lateral force L results not only from centrifugal effects, but a large component is from the crabbing of a wheelset which has a non-zero angle of attack during running with flange contact.

If weld repair of side-worn switches is undertaken, it is possible for poor workmanship to produce a ramp in the profile in the facing direction, that deflects an approaching wheel flange on to the rail head.

In extreme situations, the infrastructure may be grossly distorted or even absent; this may arise from a variety of causes, including earthwork movement (embankment slips and washouts), earthquakes and other major terrestrial disruptions, or deficient protection during work processes, among others.

Tramcars requiring low floor levels are the exception, but much benefit in vehicle guidance is lost by having unlinked wheels.

The steel-to-steel contact has a coefficient of friction that may be as high as 0.5 in dry conditions, so that the lateral force may be up to 0.5 of the vertical wheel load.

It is held down by the vertical load on the wheel V, so that if L/V exceeds the trigonometrical tangent of the flange contact angle, climbing will take place.

If the derailed vehicle is further from the track, or its configuration (such as a high centre of gravity or a very short wheelbase) make the use of ramps impossible, jacks may be used.

The sliding system consist of a beam (also called a bridge) with sleds or carriages which are moved laterally with a horizontally positioned high pressure hydraulic jack to push the vehicle back above track.

When more complex rerailing work is needed, various combinations of cable and pulley systems may be used, or the use of one or more rail-borne cranes to lift a locomotive bodily.

In extreme circumstances, a derailed vehicle in an awkward location may be scrapped and cut up on site, or simply abandoned as non-salvageable.

The primary cause was the fracture from metal fatigue of a wheel tyre; the train failed to negotiate two sets of points and struck the pier of an overbridge.

90% of the distortions could be attributed to one of the following: In the Connington South rail crash on 5 March 1967 in England, a signaller moved the points immediately in front of an approaching train.

[22] The Salisbury rail crash took place on 1 July 1906; a first class only special boat train from Stonehousepool, Plymouth England, ran through Salisbury station at about 60 miles per hour (97 km/h); there was a sharp curve of ten chains (660 feet, 200 m) radius and a speed restriction to 30 miles per hour (48 km/h).

Prominent cases were the Nuneaton rail crash in 1975 (temporary speed restriction in force due to trackwork, warning sign illumination failed),[24] the Morpeth accident in 1984 (express passenger sleeping car train took 50 miles per hour (80 km/h) restricted sharp curve at full speed; alcohol a factor; no fatalities due to the improved crashworthiness of the vehicles)[25]