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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.
D-ATC indicator used on the E233 series trains. The digital ATC system uses the track circuits to detect the presence of a train in the section and then transmits digital data from wayside equipment to the train on the track circuit numbers, the number of clear sections (track circuits) to the next train ahead, and the platform that the train will arrive at.
Today, defect detectors are typically part of the general monitoring platforms keeping track of train status. [1] Campville Defect Detector readout. A defect detector would sound like this: (This was the read out of CSX train Q452-05 by the Campville Defect Detector on April 6, 2019.
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] That ensures that a train always has time to stop before getting dangerously close to another train on the same line.
Railway interlocking is of British origin, where numerous patents were granted. In June 1856, John Saxby received the first patent for interlocking switches and signals. [2] [3]: 23–24 In 1868, Saxby (of Saxby & Farmer) [4] was awarded a patent for what is known today in North America as “preliminary latch locking”.
It automatically locks the couplers on cars or locomotives together without a rail worker having to get between the cars, and replaced the link and pin coupler, which was a major cause of railroad worker injuries and deaths. The locking pin that ensures Janney couplers remain fastened together is withdrawn manually by a worker using the "cut ...
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.
A rail break between the insulated rail joint and the track circuit feed wiring would not be detected. Failure modes that result in an incorrect "track clear" signal (known usually in North America as a "false clear") may allow a train to enter an occupied block, creating the risk of a collision. Wheel scale and short trains may also be a problem.