Balise

A balise (/bəˈliːz/ bə-LEEZ) is an electronic beacon or transponder placed between the rails of a railway as part of an automatic train protection (ATP) system.

[1] Balises are used in the KVB signalling system installed on main lines of the French railway network, other than the high-speed Lignes à Grande Vitesse.

Thus a fixed balise can notify a train of its exact location, and the distance to the next signal, and can warn of any speed restrictions.

A controllable balise is connected to a Lineside Electronics Unit (LEU), which transmits dynamic data to the train, such as signal indications.

Balises forming part of an ETCS Level 1 signalling system employ this capability.

A train travelling at maximum speed of 500 km/h (310 mph) will transmit and receive a minimum of three copies of the telegram while passing over each Eurobalise.

[5] The train's on-board computer uses the data from the balises to determine the safe speed profile for the line ahead.

As a result, the LZB system was not only used on high-speed tracks but also in commuter rail to increase throughput.

If the trains control system failed to receive an update, within 1km of the last signal, the displayed speed limit would be blanked an audio tone the driver had to respond to generated, else the trains brakes were automatically applied, the system would be see revenue service from December 1981, with the introduction of the British Rail Class 370.

[6] The development of a system using the principle of passive balises with fixed or controlled information started in 1975 by LMEricson and SRT, following an incident in Norway in 1975 (Tretten).

The French KVB replaced the external system with balises in the early 1990s to transmit a combined information for oncoming signal aspects and the allowed train speed.