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.
In addition, the following overrun protection measures are taken in consideration of the fact that trains may perform improper braking operations and overrun stop signals.
* Protection sections are secured by positioning home signals 100 m or more from the outermost shunt of the station.
* 150 m overrun protection sections or safety sidings are established inside of departure signals for incoming trains.
Electric relay interlocking devices are considered to be the ideal interlocking devices for the following reasons due to their superior safety and work efficiency.
* The various locking functions required of interlocking devices can be ensured.
* Multiple routes can be controlled with a short configuration time (approximately 6 seconds) by using electric shunting machines.
* The signal boxes for large stations can be centralized in a single location.
* Operating conditions can be understood with the control panel displays, facilitating route handling.
However, with recent advances in electronic technology, electronic interlocking devices which feature computer-based programmed route control (PRC) are tending to be adopted.
When installing interlocking devices, operation planners should take the following items into account to enable the smooth execution of yard work from the viewpoint of the users.
* Methods of using departure and arrival tracks and specification of through tracks (main lines)
* Signal installment positions and overrun protection section ranges and directions
* Confirming the effective length of the track
* Shunting work methods and telecommunication facilities for communication
