Signalling

Railway signalling is a system used to control railway traffic safely to prevent trains from colliding. Being guided by fixed rails, trains are uniquely susceptible to collision since they frequently operate at speeds that do not enable them to stop quickly or, in some cases, within the driver's sighting distance.

Most forms of train control involve movement authority being passed from those responsible for each section of a rail network (e.g., a signalman or stationmaster) to the train crew. The set of rules and the physical equipment used to accomplish this control determine what is known as the method of working (UK), method of operation (U.S.) or safeworking (Aus.). Not all methods require the use of signals, and some systems are specific to single track railways. The signalling process is traditionally carried out in a signal box (or interlocking tower (U.S.)), a small building that houses the lever frame required for the signalman to operate switches and signal equipment. These are placed at various intervals along the route of a railway, controlling specified sections of track. More recent technological developments have made such operational doctrine superfluous, with the centralization of signalling operations to regional control rooms. This has been facilitated by the increased use of computers, allowing vast sections of track to be monitored from a single location.