Le Crocodile

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The French (SNCF) and Belgian (SNCB) railways use an alert system more or less equal to the British Automatic Warning System (AWS), called the Répétition du Signal en Cabine (French for "Signal Repetition in Driver's Cab").

Crocodile

The signal repetition is done by the crocodile, an electrical contact placed between the rails (in the four-foot or 1.22m way) to provide warnings in the locomotive cab. It is distinctively French, originating on the Chemins de Fer du Nord around 1872, spreading throughout France and penetrating even into Belgium and Luxemburg after 1900. It was intended principally to provide evidence of the alertness of the driver, not to act to control a train automatically. Contact is made with a metallic brush mounted beneath an engine passing over it.

The crocodile is an invention of the engineers Lartigue and Forest. Originally it was placed 100-200 metres in rear of a distant signal, usually a red disc of "deferred stop". When recording of cab signals was introduced, the crocodile was moved closer to the signal, often directly opposite it, to reduce the chance of a change of the signal between the time the locomotive passed over the crocodile and when the locomotive actually passed the signal. If a signal changed suddenly to a warning aspect in the face of the driver, it would appear that he had not noticed it and had been surprised, when that was not the case.

The crocodile can send 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 (=on) signal), corresponding to a warning signal, applies a +20V voltage to the crocodile and sounds a horn in the driver's cab. Then unless the driver presses a button within 5 seconds, a penalty brake is applied.

- the "Répétition Signal Ouvert" (which literally means: repetition of opened (=off) signal), corresponding to a cleared signal, applies a -20V voltage to the crocodile and sounds a gong in the driver's cab.