Interlocking - Configuration and Use

Configuration and Use

A minimal interlocking consists of signals, but usually includes additional appliances like switches (points in UK parlance), derails, crossings at grade and movable bridges. Some of the fundamental principles of interlocking include:

• Signals may not be operated to permit conflicting train movements to take place at the same time.
• Switches and other appliances in the route must be properly 'set' (in position) before a signal may allow train movements to enter that route.
• Once a route is set and a train is given a signal to proceed over that route, all switches and other movable appliances in the route are locked in position until either
  • the train passes out of the portion of the route affected, or
  • the signal to proceed is withdrawn and sufficient time has passed to ensure that a train approaching that train has had opportunity to come to a stop before passing the signal.