Le Crocodile
Encyclopedia
France
The French Republic , The French Republic , The French Republic , (commonly known as France , is a unitary semi-presidential republic in Western Europe with several overseas territories and islands located on other continents and in the Indian, Pacific, and Atlantic oceans. Metropolitan France...
railway signalling
Railway signalling
Railway signalling is a system used to control railway traffic safely, essentially to prevent trains from colliding. Being guided by fixed rails, trains are uniquely susceptible to collision; furthermore, trains cannot stop quickly, and frequently operate at speeds that do not enable them to stop...
a crocodile is a component of a train protection system called Répétition des Signaux (French
French language
French is a Romance language spoken as a first language in France, the Romandy region in Switzerland, Wallonia and Brussels in Belgium, Monaco, the regions of Quebec and Acadia in Canada, and by various communities elsewhere. Second-language speakers of French are distributed throughout many parts...
for "signal repetition"). This system is used by French (SNCF
SNCF
The SNCF , is France's national state-owned railway company. SNCF operates the country's national rail services, including the TGV, France's high-speed rail network...
), Belgian (NMBS/SNCB) and Luxemburger (CFL)
Chemins de Fer Luxembourgeois
Société Nationale des Chemins de Fer Luxembourgeois is the national railway company of Luxembourg. In 2005, the company carried approximately 14.1 million passengers and 11.7 million tonnes of goods...
railways and is functionally similar to the British Automatic Warning System
Automatic Warning System
The Automatic Warning System is a form of limited cab signalling and train protection system introduced in 1956 in the United Kingdom to help train drivers observe and obey signals. It was based on a 1930 system developed by Alfred Ernest Hudd and marketed as the "Strowger-Hudd" system...
(AWS).
Communication between the ground-based signalling system and the in-cab equipment is made by the crocodile, an electrical contact placed between the rails (in the four-foot or 1.22m way) and a metallic brush mounted beneath the locomotive cab. It is distinctively French, originating on the Chemins de Fer du Nord 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 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 signal"), corresponding to a warning signal, applies a +20V voltage to the crocodile causing horn to sound 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 signal"), corresponding to a cleared signal, applies a -20V voltage to the crocodile causing a gong to sound in the driver's cab.