A crocodile is a component of train protection systems used in France and Belgium. It works similarly to the Automatic Warning System (AWS) used in the United Kingdom.
The crocodile can provide two different pieces of information to the driver, according to the aspect of the corresponding signal:
The répétition signal fermé (which literally means "repetition of closed signal"), corresponding to a caution or danger signal, applies a +20 V voltage to the crocodile, causing a warning horn to beep in the driver's cab. Then, unless the driver pushes the acknowledgement button within five seconds, the emergency brakes are applied automatically.
The répétition signal ouvert (which literally means "repetition of opened signal"), corresponding to a proceed signal, applies a −20 V voltage to the crocodile, causing a bell to ring in the driver's cab for old machines.
Communication between the ground-based signalling system and the in-cab equipment is made by the crocodile, an electrical contact placed between the rails and a...
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