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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.
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.
To clip and scotch a set of railway points (Amer. a switch) uses two pieces of equipment to temporarily lock a set of points into a particular position. [1] The point clip clamps the end of a moving rail (the switch rail ) of a set of points to its associated stock rail , and the scotch is a timber wedge used to ensure that the other moving ...
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”.
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.
The system is set up by having an axle counter sensor installed at each end of a section. As each train axle passes the axle counter sensor at the start of the section, a counter increments. An axle counter sensor comprises two independent sensors (so the device can detect the direction and speed of a train by the order and time in which the ...
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.
On straight track, the link and pin coupler is used. Since the vertical curve between the straight track sections and the ramp between the lock chambers has a very small radius, the difference in height would be too great for a link and pin coupler, so the locomotives must be pushed through these sections uncoupled by using the side buffers.