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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.
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 RTC can also issue special permissions to trains via radio. In order to pass signals set at stop (Rule 564), reverse direction within a block (Rule 577) or enter the main line at a manual switch not equipped with a signal (Rule 568), the train crew must copy the RTC's instructions and repeat them back correctly before being allowed to proceed.
Semi-automatic signals do not have a number plate, but can display an explicit "restricted proceed"-type signal. Other types of signals include train order signals, manual block signals or signals governing special safety appliances such as slide fences, non-interlocked sidings, road crossings, etc. These are much less common than the three ...
The invention of train detection systems such as track circuits allowed the replacement of manual block systems such as absolute block with automatic block signalling. Under automatic block signalling, signals indicate whether or not a train may enter a block based on automatic train detection indicating whether a block is clear.
The system also has automatic and manual "key-by" red signals where the conductor can insert a physical key into the wayside block signal, changing the signal indication from red to yellow. The signals involve the operation of an automatic stop with an automatic or manual release, then to proceed with caution, with preparations to stop in case ...
CBTC is a signalling standard defined by the IEEE 1474 standard. [1] The original version was introduced in 1999 and updated in 2004. [1] The aim was to create consistency and standardisation between digital railway signalling systems that allow for an increase in train capacity through what the standard defines as high-resolution train location determination. [1]
CTC automatic block signals along the Union Pacific Railroad Yuma Subdivision, Coachella, California. CTC makes use of railway signals to convey the dispatcher's instructions to the trains. These take the form of routing decisions at controlled points that authorize a train to proceed or stop.