Moving block

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The safety distance (safe-braking distance) between trains in fixed block and moving block signalling systems

In railway signalling, a moving block is a signalling block system where the blocks are defined in real time by computers as safe zones around each train. This requires both knowledge of the exact location and speed of all trains at any given time, and continual communication between the central signalling system and the train's cab signalling system. Moving block allows trains to run closer together (reduced headway) while maintaining required safety margins, thereby increasing the line's overall capacity. It may be contrasted with fixed block signalling systems.

Communications Based Train Control (CBTC) or Transmission Based Signalling (TBS) is required to detect the exact location of trains and to transmit back the permitted operating speed to enable this flexibility.[1] Information about train location can be gathered through active and passive markers along the tracks, and train-borne tachometers and speedometers. Satellite-based systems are not used because they do not work in tunnels.

Another version of the moving block system would be the location computers on the trains itself. Each train determines its location in relation to all the other trains and sets its safe speeds using this data. Less wayside equipment is required compared to the off-train system but the number of transmissions is much greater.[citation needed]



Moving block is in use on several London Underground lines, including the Victoria,[citation needed] Jubilee, and Northern lines, and parts of the sub-surface lines.[2] In London it is also used on the Docklands Light Railway[3] and the core section of the Elizabeth line.[4] New York City Subway's BMT Canarsie Line (L train), Tren Urbano (Puerto Rico),[5] Singapore's MRT, and Vancouver's SkyTrain, also employ moving block signalling. It is also used by the Hong Kong MTR, on the Tuen Ma line, Disneyland Resort line, South Island line and the East Rail line .[6]


It was supposed to be the enabling technology on the modernisation of Britain's West Coast Main Line which would allow trains to run at a higher maximum speed (140 mph or 230 km/h), but the technology was deemed not mature enough, considering the large number of junctions on the line, and the plan was dropped.[7] It forms part of the European Rail Traffic Management System's level-3 specification for future installation in the European Train Control System, which will at level 3 feature moving blocks that allow trains to follow each other at exact braking distances.


  1. ^ "Moving Block — The Theory". ATP Beacons and Moving Block. Railway Technical Web Pages. 17 November 2016. Archived from the original on 9 February 2009. Retrieved 17 November 2016.
  2. ^ White, Steve; Abbott, James (2017-10-26). "Sub-surface transformation". Modern Railways. Retrieved 2022-07-24.
  3. ^ Lockyear, M.J. (1998). "The application of a transmission based moving block automatic train control system on Docklands Light Railway". International Conference on Developments in Mass Transit Systems. London, UK: IEE. 1998: 51–61. doi:10.1049/cp:19980097. ISBN 978-0-85296-703-4.
  4. ^ "Signalling and Testing on the Elizabeth line" (PDF). Crossrail. November 2019. Retrieved 24 July 2022.
  5. ^ "Tren Urbano - Railway Technology".
  6. ^ "The Jubilee Line Upgrade" (PDF). London Underground Railway Society. 13 October 2009. Retrieved 22 November 2009.
  7. ^ "Background to the West Coast Modernisation Programme — The West Coast Route Modernisation began as a private sector programme" (PDF). The Modernisation of the West Coast Main Line. Comptroller and Auditor General, National Audit Office. 22 November 2006. p. 26. Archived (PDF) from the original on 26 November 2016. Retrieved 26 November 2016.