Railway signalling

Railway signalling uses visual, audible, or electronic instructions and systems to regulate train movements, maintain separation, and coordinate routes safely.

Railway signal: A device that conveys instructions or indications to railway staff or train operators. The visible or audible instruction is one part of a larger signalling system.
Railway track: A structure of rails, sleepers, and supporting layers that guides and carries railway vehicles. The physical route determines where trains can travel and where occupancy must be detected.
Automatic block signaling: A railway signalling method in which track occupancy automatically controls signals protecting successive blocks. It reduces dependence on manual decisions when managing trains on busy lines.
Fixed block system: A train-control arrangement that divides track into fixed sections and restricts occupancy to maintain separation. Its fixed sections contrast with systems that calculate separation continuously.
Interlocking: A system that prevents railway signals and switches from being set to unsafe combinations. It prevents a route from being cleared while points or conflicting routes make it unsafe.
Railway switch: A movable section of railway track that directs a train from one track to another. Signals must account for switch position before authorizing a route through a junction.
Cab signalling: A system that displays movement authority or speed information inside the train cab. It conveys instructions where lineside signals are difficult to see or too widely spaced.
Centralized traffic control: A railway operating system in which a dispatcher remotely controls signals and switches over a territory. It centralizes route decisions that local signal boxes once handled separately.
Track circuit: An electrical circuit that detects a train by using its wheels and axles to shunt current between the rails. Track circuits report whether a section is occupied, informing signal aspects and route control.
Railway block: A defined section of railway track whose occupancy is controlled to maintain train separation. Signals commonly govern entry to blocks rather than granting unrestricted movement.

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