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.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.[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.
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