The system gives audio visual warning to the gate man about an approaching train. This warning ensures that the gate is not closed too early inconveniencing the road users or too late detaining the train by not closing the Gate when a train approaches gate signal. This warning is prescribed for interlocked gates.
Approaching Train can be detected using occupancy of a nominated track circuit. To provide optimum time for gate man to close the gate, a track circuit, which is already available at about 3 km, is selected. However, if there is no track circuit at 3 km, nearest existing track circuit is considered. This is to avoid maintenance of a track circuit exclusively for the purpose of approach warning. In practical situations, the track circuit immediately after the last stop signal of the station is used as approach track for all the LC gates in the block section. Sometimes if the distance between the first LC gate and the track circuit is too less, approach warning is given as soon as the last stop signal is cleared. In both the cases, it is a digital signal (track occupied and signal yellow or green lamp lit) whose state of change generates approach warning.