High Quality Content by WIKIPEDIA articles! A track circuit is a simple electrical device used to detect the presence or absence of a train on rail tracks, used to inform signallers and control relevant signals. The basic principle behind the track circuit lies in the connection of the two rails by the wheels and axle of locomotives and rolling stock to short out an electrical circuit. This circuit is monitored by electrical equipment to detect the presence or absence of the trains. Since this is a safety appliance, fail-safe operation is crucial; therefore the circuit is designed to indicate the presence of a train when failures occur. On the other hand, false occupancy readings are disruptive to railroad operations and are to be minimized.