Moving block

Article summary

In railway signalling, a moving block is a signalling block system under which the "blocks", or safe zones around trains, are defined in real time by computers. That requires both the knowledge of the exact location and the speed of all trains at any given time, as well as continual communication between the central signalling system and the signalling system in the train cab. Moving block allows trains to run closer together (reduced headway) while maintaining the required safety margins, thereby increasing the line's overall capacity. It can be contrasted with fixed block signalling systems. Communications Based Train Control (CBTC) and Transmission Based Signalling (TBS) are two signalling standards that can detect the exact location of trains and transmit back the permitted operating speed to enable the required flexibility. The European Train Control System (ETCS) also has the technical specifications to allow moving block operations, though no system uses it currently, apart from test tracks. Information about train location can be gathered through active and passive markers along the tracks, as well as train-borne tachometers and speedometers. Satellite-based systems are not used because they cannot work in tunnels. Traditionally, moving block works by having a series of transponders in the rail corridor that have a known location.…

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