Catch points

Interlocking is used to make sure that the signal cannot be set to allow passage onto the main line until the trap points have been aligned to ensure this movement can take place.

Trap points should preferably be positioned to ensure that any unauthorised vehicle is stopped a safe distance from the main line.

In some cases, on a track that is only traversed by uphill traffic, trailing point blades are held in a position to derail any vehicle travelling downhill.

[2] In these cases, a lever may be provided to temporarily override the catch points and allow safe passage down the gradient in certain controlled circumstances.

The use of catch points became widespread in the United Kingdom after the Abergele rail disaster (1868), where runaway wagons containing paraffin oil (kerosene) collided with an express train.

In such cases, a pair of single catchpoints of left and right hand may be provided to derail the overrunning train without directing it to either side.

[2] A cheap and simple alternative to catch points or a derail is a chock block, which is a piece of timber that can be positioned and locked over one of the rails at the end of a siding to protect the main line from runaways.

[3] In 2010, in snowy conditions, at Carrbridge, a Class 66 passed a red signal as well as catch points, leading to the train going down the embankment, injuring the two crew on board.

Trap points and a sand drag (left) and catch points (right) protect the entrance to a single track on a steep grade.
Diagram showing the use of trap points to protect the main line at the exit of a siding
An insulated track circuit interrupter fitted to trap points
RAIB accident investigation image of a cement wagon derailed by trap points at Clitheroe, 9 March 2020, successfully protecting the adjacent running lines (left)
View of a track from a sand drag , in the Montreal Metro beyond the Honoré-Beaugrand station terminus
A British Rail Class 165 that was derailed by a set of trap points at London Paddington station , June 2016. The train suffered severe damage to the rear driving unit and also damaged a stanchion by colliding with it.