A system of signalling, for Single lines, which is a BLOCK system where the Starting signals for entering the section from either end is controlled by the track circuit throughout the section. The object of the system is to prevent more than one train being in the section at one time, each signal box is equipped with a device for transmitting and receiving train working signals, as well as indicators to show direction of travel.
In use the following occurs, When a train is ready to be despatched into the section in advance, the signal man would send the signal for accept train described by sending
3 pause 1
The signal man in advance replies with
3 pause 1, and moves his accepting lever to the reverse position, an indicator in the despatching signal box lights and the signal man there can clear his starting signal by moving his Starting signal lever to the reverse position.
