Since every block is fixed by the infrastructure, these systems are referred to as fixed block systems. Each block is protected by signals that prevent a train entering an occupied block. Traditional legacy signalling systems are historically based in the detection of the trains in discrete sections of the track called ‘blocks’. The main objective of CBTC is to increase capacity by safely reducing the time interval (headway) between trains travelling along the line. As a result of this operators are now focused on maximising train line capacity. Metros (and other railway systems) are able to improve headways while maintaining or even improving safety.Ī CBTC system is a “continuous, automatic train control system utilizing high-resolution train location determination, independent of 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 theIEEE 1474 standard.Ĭity and population growth increases the need for mass transit transport and signalling systems need to evolve and adapt to safely meet this increase in demand and traffic capacity. This results in a more efficient and safe way to manage the railway traffic. By means of the CBTC systems, the exact position of a train is known more accurately than with the traditional signaling systems. In the meantime, multiple trains will have been safely stopped at red signals but we do everything we can to get normal train services up and running again.Communications-Based Train Control (CBTC)Ĭommunications-Based Train Control (CBTC) is a railway signaling system that makes use of the telecommunications between the train and track equipment for the traffic management and infrastructure control. After testing the equipment is working, the fault team clear the area.Once they’ve done this, they can repair or replace equipment.We send a team of technicians to find out what’s happened.The signalling system knows there’s a failure.Typically, when such events happen to the signalling system, the way we deal with them is something like this: However, in such a circumstance the trains must run at a reduced speed in case there is an obstruction. Usually, we can keep some train services moving following a track circuit failure – by using manual methods to signal trains. Meanwhile, flooding, contaminated ballast, or other problems with insulation between the rails can bypass the circuit crushed leaves or ice on the rails can form an insulating layer that makes the circuit unreliable. Potential causes of failures include a broken rail, a blown fuse, faulty electrical parts, cable theft, or a loose connection, all of which form a break in the track circuit. This results in delays because the system can only allow train movements when it knows it is safe to do so – when the track ahead is clear of other trains. Normally, a failed track circuit will act as if a train is present. When a train runs on a section, it causes the current to bypass the relay, which tells the signalling system there’s a train.Ī track circuit failure can delay trains because the signalling system is designed to fail to a safe state. We use rails to link a power source at one end of a section with a relay at the other end. Signals, which require information from track circuits to safely move trains around the networkĮach section of the railway forms part of an electric circuit, which runs a current from one rail to the other through a relay. The broader signalling system also includes systems controlling the railway and operating the timetable points (movable sections of track) that control the directions trains take and determine what movements are safe, and train protection systems that guard against mistakes by drivers. This information then helps the signalling system know if it’s safe for another train to proceed. What are track circuits? How do they keep the railway safe? And why do they sometimes delay journeys?Ī track circuit forms part of the broader signalling system, which comprises many parts to enable trains to move safely around the network.Ī track circuit itself is an electrical system that detects the absence of a train on a section of track.
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