SelTrac

SelTrac is a digital railway signalling technology used to automatically control the movements of rail vehicles. It was the first fully automatic moving-block signalling system to be commercially implemented.

What is now branded as SelTrac was originally developed in the 1970s by Standard Elektrik Lorenz (the "SEL" in the name) for the Krauss-Maffei Transurban, an automated guideway transit system proposed for the GO-Urban network in the Greater Toronto Area in Canada. Although the GO-Urban project failed, the Transurban efforts were taken over by an Ontario consortium led by the Urban Transportation Development Corporation (UTDC), and adapted to become its Intermediate Capacity Transit System (ICTS). This technology was first used on the SkyTrain network in Vancouver, British Columbia and the Scarborough RT in Toronto, Ontario.

SelTrac was primarily sold and developed by Alcatel, through a Toronto subsidiary. SelTrac is now sold by Thales, after it purchased many of Alcatel's non-telephony assets. New versions were made for different markets, and today SelTrac is used for rolling stock control around the world.

The original SelTrac system was based on inductive loops that provided a communications channel as well as positioning information. Normally an inductive loop is used solely as a communications system, with electromagnets on the vehicles or stations inducing currents in the loop that can be read at a distant location. In the case of SelTrac, the central computer sent data to the vehicles at 1200 bit/s on a 36 kHz carrier while the vehicles had 600 bit/s on a 56 kHz carrier. Separate antennae are used for transmission and reception.

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