In railway signalling, a moving block is a

signalling block system Signalling block systems enable the safe and efficient operation of railways by preventing collisions between trains. The basic principle is that a track is broken up into a series of sections or "blocks". Only one train may occupy a block at a ...

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 Headway is the distance or duration between vehicles in a transit system measured in space or time. The ''minimum headway'' is the shortest such distance or time achievable by a system without a reduction in the speed of vehicles. The precise defi ...

) while maintaining required safety margins, thereby increasing the line's overall capacity. It may be contrasted with

fixed block Railway signalling (), also called railroad signaling (), is a system used to control the movement of railway traffic. Trains move on fixed rails, making them uniquely susceptible to collision. This susceptibility is exacerbated by the enor ...

signalling systems.

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 accurat ...

(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. 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.

Implementation

Urban

Moving block is in use on several

London Underground The London Underground (also known simply as the Underground or by its nickname the Tube) is a rapid transit system serving Greater London and some parts of the adjacent counties of Buckinghamshire, Essex and Hertfordshire in England. The U ...

lines, including the Victoria,

Jubilee A jubilee is a particular anniversary of an event, usually denoting the 25th, 40th, 50th, 60th, and the 70th anniversary. The term is often now used to denote the celebrations associated with the reign of a monarch after a milestone number of ...

, and Northern lines, and parts of the sub-surface lines. In London it is also used on the

Docklands Light Railway The Docklands Light Railway (DLR) is an automated light metro system serving the redeveloped Docklands area of London, England and provides a direct connection between London's two major financial districts, Canary Wharf and the City of L ...

and the core section of the

Elizabeth line The Elizabeth line is a high-frequency hybrid urban–suburban rail service in London and its suburbs. It runs services on dedicated infrastructure in central London from the Great Western Main Line west of Paddington to and via Whitechapel t ...

. New York City Subway's

BMT Canarsie Line The BMT Canarsie Line (sometimes referred to as the 14th Street–Eastern Line) is a rapid transit line of the B Division (New York City Subway), B Division of the New York City Subway system, named after its terminus in the Canarsie, Brooklyn, ...

(), Tren Urbano (Puerto Rico), 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 The Tuen Ma line () is a rapid transit line that forms part of the Mass Transit Railway (MTR) system in Hong Kong. Coloured brown on the map, the Tuen Ma line is in length, making it the longest line of the MTR network. It has a total of ...

, Disneyland Resort line, South Island line and the

East Rail line The East Rail line () is one of ten lines of the Mass Transit Railway (MTR) system in Hong Kong. It used to be one of the three lines of the Kowloon–Canton Railway (KCR) network. It was known as the KCR British Section () from 1910 to 1996 ...

Inter-city

It was supposed to be the enabling technology on the modernisation of Britain's

West Coast Main Line The West Coast Main Line (WCML) is one of the most important railway corridors in the United Kingdom, connecting the major cities of London and Glasgow with branches to Birmingham, Liverpool, Manchester and Edinburgh. It is one of the busiest ...

which would allow trains to run at a higher maximum speed (), but the technology was deemed not mature enough, considering the large number of junctions on the line, and the plan was dropped. It forms part of the European Rail Traffic Management System's level-3 specification for future installation in the

European Train Control System The European Train Control System (ETCS) is the signalling and control component of the European Rail Traffic Management System (ERTMS). It is a replacement for legacy train protection systems and designed to replace the many incompatible ...

, which will at level 3 feature moving blocks that allow trains to follow each other at exact braking distances.

References

{{Railwaysignalling Railway signalling block systems