Indicated by absence of number plate on mast. The signals described in this document are all Block Signals , i.e. they govern trains entering the following Block . A Block is the line between two consecutive Block Signals. Distant Signals are signals on the approach to signaled territory, governing the approach to the first Block Signal. A Distant Signal does not indicate the condition of the track between the Distant Signal and the Block Signal.
Any train needs to have some sort of permission to occupy a main track.
The required permission depends on the type of operation in effect for that main track. The type of operation for any main track is listed in the employee timetable, as explained below. Track Bulletins may at any time modify the operation type. In the descriptions below, the following symbols are used. A train may occupy a main track in CTC territory if it has been permitted to do so by signal indication.