A crocodile is a component of

train protection system A train protection system is a railway technical installation to ensure safe operation in the event of human error. Development Train stops The earliest systems were train stops, as still used by the New York City Subway, the Toronto rapid ...

s used in

France France, officially the French Republic, is a country located primarily in Western Europe. Overseas France, Its overseas regions and territories include French Guiana in South America, Saint Pierre and Miquelon in the Atlantic Ocean#North Atlan ...

and

Belgium Belgium, officially the Kingdom of Belgium, is a country in Northwestern Europe. Situated in a coastal lowland region known as the Low Countries, it is bordered by the Netherlands to the north, Germany to the east, Luxembourg to the southeas ...

. It works similarly to the

Automatic Warning System Automatic Warning System (AWS) is a railway safety system invented and predominantly used in the United Kingdom. It provides a train driver with an audible indication of whether the next Railway_signal, signal they are approaching is clear or a ...

(AWS) used in the

United Kingdom The United Kingdom of Great Britain and Northern Ireland, commonly known as the United Kingdom (UK) or Britain, is a country in Northwestern Europe, off the coast of European mainland, the continental mainland. It comprises England, Scotlan ...

. The crocodile can provide two different pieces of information to the driver, according to the aspect of the corresponding signal: * The (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 (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 metallic brush mounted beneath the locomotive cab. It is distinctively French, originating on the around 1872, spreading throughout France and penetrating into Belgium and Luxembourg after 1900. It was intended principally to provide evidence of the alertness of the driver, not to act to control a train automatically. The crocodile is an invention of the engineers Lartigue and Forest. Originally it was placed 100–200 metres in front of a distant signal, usually a red disc of "deferred stop". When recording of cab signals was introduced, the device was moved closer to the signal, most 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 caution or danger aspect in the face of the driver, it would appear that they had not noticed it and had been surprised, when that was not the case.

References

{{Railway signalling Train protection systems