Treadle (railway)

In railway signalling, a treadle is a mechanical or electrical device that detects that a train wheel has passed a particular location.

In situations where track circuits are unreliable due to rusty rails, for example adjacent to buffer stops and catch points, a long treadle bar is used.

It remains depressed for a period of several seconds, so that a train with many axles does not unduly damage the unit.

An electronic treadle uses the disruption of an electromagnetic field to detect an axle, rather than a depression bar.

[2] The biggest flaw in the Whitworth automatic signal is probably that it had no redundancy, and a single stone might jam it.