The track circuit is a fundamental component of the fail-safe system on railway networks as its main function is to detect, whatever the conditions, a train on a track. This function is carried out by ALSTOM’s High Voltage Impulse Track Circuit on more than thirty major railways in the world.

A HVITC includes:

A transmitter which generates impulses with a given shape, amplitude and recurrence frequency injected into the tracks by means of a matching isolating transformer, and a receiver which detects at the other end of the track section, the specific signal and operates the fail-safe relay if the specific signal responds to the correct positive and negative amplitudes.