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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 ...
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.
Like the manual block systems outlined above, automatic systems divide the route into fixed blocks. At the end of each block, a set of signals is installed, along with a track-side sensor. 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.
The tuned circuit often incorporates the circuit to either apply the transmitted signal to the track or recover the received signal from the other end of the section. Consider a railway with two block sections as in the diagram. Section 1 has frequency A injected at the left-hand end and received at the right-hand end.
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 ...
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
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 ...
Signals in CTC territory are one of two types: an absolute signal, which is directly controlled by the train dispatcher and helps design the limits of a control point, or an intermediate signal, which is automatically controlled by the conditions of the track in that signal's block and by the condition of the following signal. Train dispatchers ...