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In absolute block working, a block section (or simply section) is a section of railway line between one signal box and another – in the typical absolute block, lines are paired, with an up – towards London (or in Scotland, Edinburgh) – and a down line in the opposite direction.
When a train passes the sensor, the signals are triggered to display the "block occupied" aspect on the signals at either end of that block. In most systems the signals do not immediately return to the "block empty" aspect when the train leaves, instead there is some sort of mechanical delay that retains the block occupied aspect, or more ...
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.
This was called the "absolute block system". 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 ...
Mechanical signalling in all States followed British practice using route signalling with slight differences between States. The basic running signal was the Home signal, an absolute stop signal with a red arm. Route signalling was used to indicate the line to be taken at junctions. Advance warning was given by a Distant signals.
The modern-day system mostly uses two, three, and four aspect colour-light signals using track circuit – or axle counter – block signalling. [1] [2] It is a development of the original absolute block signalling that is still being used on many secondary lines. The use of lineside signals in Britain is restricted to railways with a maximum ...
In Canada, non-signalled and Automatic Block Signal (ABS) territories are operated according to OCS rules. The only authority for movement in OCS territory is possession of a clearance or track occupancy permit (TOP). While the line might be equipped with signals (ABS), these signals are unsupervised and uncontrolled by the RTC.
Absolute block signalling A British signalling scheme 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, used on lines which lack automatic block signalling [1] Aspect The indication displayed by a colour-light signal (e.g. a yellow aspect) Autocoach