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Automatic block signaling (ABS), spelled automatic block signalling or called track circuit block (TCB [1]) in the UK, is a railroad communications system that consists of a series of signals that divide a railway line into a series of sections, called blocks. The system controls the movement of trains between the blocks using automatic signals.
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 time, [citation needed] and the blocks are sized to allow a train to stop within them. [1]
Fixed mechanical signals began to replace hand signals from the 1830s. These were originally worked locally, but it later became normal practice to operate all the signals on a particular block with levers grouped together in a signal box. When a train passed into a block, a signalman would protect that block by setting its signal to 'danger ...
Absolute block signalling is a British signalling block system designed to ensure the safe operation of a railway by allowing only one train to occupy a defined section of track (block) at a time. [1]
Direct Traffic Control, or DTC, is similar to TWC, except that the rail line is divided up into predefined blocks—somewhat similar to ABS blocks without the signals—and dispatchers authorize trains to proceed in a specified number of blocks. Only one train may occupy a stretch of authority (which may consist of a single block or a stretch ...
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 ...
The train could then proceed, and a second train could follow. In the earliest days, the second train could proceed after a designated time interval, as on double lines at the time. However, after the Armagh rail disaster of 1889, block working became mandatory. Seeing the train staff provided assurance that there could be no head-on collision.
Traditional signalling systems detect trains in discrete sections of the track called 'blocks', each protected by signals that prevent a train entering an occupied block. Since every block is a fixed section of track, these systems are referred to as fixed block systems.