The comprehensive network of track circuits, relays, switch machines, and visual indicators that dictate train authority and speed. Signalling prevents collisions by maintaining absolute blocks between trains and routing them safely through junctions. It ranges from traditional mechanical semaphores to advanced computer-based positive train control networks.
We're running at restricted speed all the way to the yard because the signalling is down through the entire valley.
Related terms
Centralized traffic control
A signal system that allows a single dispatcher to line switches and signals across hundreds of miles of track.
Block system
A method of safely spacing trains by dividing the track into segments and controlling entry to each.
PTC
Positive train control: an onboard and wayside system that stops a train before it breaks a speed limit or authority.