Interlocking devices are used to mutually interlock blocking devices with signal devices, and signal devices with shunting devices, etc. Interlocking devices function as comprehensive safety devices in stations to ensure safe train operation.
The basic safety conditions required of interlocking devices are described below.
Interlocking devices must ensure that:
* All shunts over the route are open and locked in the correct direction.
* The route is not blocked by other trains or cars.
* There are no trains or cars over the route.
* The above locking relationships are secured while the trains are running.
