Communications-based train control

Communications-based train control (CBTC) is a railway signaling system that uses telecommunications between the train and track equipment for traffic management and infrastructure control. CBTC allows a train's position to be known more accurately than with traditional signaling systems. This makes railway traffic management safer and more efficient. Metros (and other railway systems) are able to reduce headways while maintaining or even improving safety. A CBTC system is a "continuous, automatic train control system utilizing high-resolution train location determination, independent from track circuits; continuous, high-capacity, bidirectional train-to-wayside data communications; and trainborne and wayside processors capable of implementing automatic train protection (ATP) functions, as well as optional automatic train operation (ATO) and automatic train supervision (ATS) functions," as defined in the IEEE 1474 standard. The main objective of CBTC is to increase track capacity by reducing the time interval (headway) between trains. Traditional signalling systems detect trains in discrete sections of the track called 'blocks', each protected by signals that prevent a train entering an occupied block. Since every block is a fixed section of track, these systems are referred to as fixed block systems. In a moving block CBTC system the protected section for each train is a "block" that moves with and trails behind it, and provides continuous communication of the train's exact position via radio, inductive loop, etc. As a result, Bombardier opened the world's first radio-based CBTC system at San Francisco airport's automated people mover (APM) in February 2003. A few months later, in June 2003, Alstom introduced the railway application of its radio technology on the Singapore North East line. Previously, CBTC has its former origins in the loop based systems developed by Alcatel SEL (now Thales) for the Bombardier Automated Rapid Transit (ART) systems in Canada during the mid-1980s.