1) Train detection system 
An axle counter is a device on a railway that detects the passing of a train in lieu of the more common track circuit. A counting head (or `detection point`) is installed at each end of the section, and as each axle passes the head at the start of the section, a counter increments. A detection point comprises two independent sensors, therefore t.....
a system using counting points and a counter which detects the occupancy of a section of track by comparing the number of axles which enter the section with the number of axles which leave the section, parity of the numbers being necessary to give a clear indication
method of train detection as alternative to Track Circuit