Derail

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A Derail is a device used to prevent fouling of a track by unauthorized movements of trains or unattended rolling stock. It works (as the name suggests) by derailing the equipment if it attempts to roll past the derail.

There are two basic forms of derail. The most common North American form is a wedge which fits over the top of the rail. If a car or locomotive attempts to roll over it, the wheel flange is lifted over the rail to the outside, derailing it. When not in use, the derail folds away, leaving the rail unobstructed. It can be manually or remotely operated; in the former case it will have a lock applied to prevent it from being moved by unauthorized personnel.

In British usage the catch point is more common. This is basically a complete or partial switch which directs the errant trains or cars away from the track. This form is seen in North American as well, but it does not have a special name.

Derails may be applied:

where sidings meet main lines or other through tracks
at junctions or other crossings to protect the interlocking against unauthorized movement

Derail

See also