So, the trains continuously receive information regarding the distance to the preceding train and are then able to adjust their safety distance accordingly.įrom the signalling system perspective, the first figure shows the total occupancy of the leading train by including the whole blocks which the train is located on. These points are communicated to make the trains automatically and continuously adjust their speed while maintaining the safety and comfort (jerk) requirements. It also enables the wayside equipment to define the points on the line that must never be passed by the other trains on the same track. This information allows calculation of the area potentially occupied by the train on the track. This status includes, among other parameters, the exact position, speed, travel direction and braking distance. In the modern CBTC systems the trains continuously calculate and communicate their status via radio to the wayside equipment distributed along the line. For main lines, a similar system might be the European Railway Traffic Management System ERTMS Level 3 (not yet fully defined). So, for clarity and to keep in line with the state-of-the-art solutions for operator’s requirements, this article only covers the latest moving block principle based (either true moving block or virtual block, so not dependent on track-based detection of the trains) CBTC solutions that make use of the radio communications.ĬBTC systems are modern railway signaling systems that can mainly be used in urban railway lines (either light or heavy) and APMs, although it could also be deployed oncommuter lines. Moreover, it is important to highlight that not all the systems using radio communication technology are considered to be CBTC systems. However, there have been relevant improvements since then, and currently the reliability of the radio-based communication systems has grown significantly. This technology, operating in the 30–60 kHz frequency range to communicate trains and wayside equipment, was widely adopted by the metro operators in spite of someelectromagnetic compatibility (EMC) issues, as well as other installation and maintenance concerns.Īs with new application of any technology, some problems arose at the beginning mainly due to compatibility and interoperability aspects. Besides, the trains themselves are continuously communicating their exact position to the equipment in the track by means of a bi-directional link, either inductive loop or radio communication. Unlike the traditional fixed block systems, in the modern moving block CBTC systems the protected section for each train is not statically defined by the infrastructure (except for the virtual block technology, with operating appearance of a moving block but still constrained by physical blocks). 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. 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.
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