Changes

A system that relies upon the two rails forming a pair of electrical conductors along a designated section of railway. A power source (often a battery) is provided at one end and an electrical detector (often a relay) is provided at the other end. When the section of track is unoccupied the detector is energised. When the section of track becomes occupied by a train the wheels and axles short circuit the power source hence de-energising the detector and thus aid safe train operation.

A useful adjuct of this system is it can detect certain broken rail conditions thus further improving safety.