The object of Single Line Working is to prevent Rail Traffic travelling in opposite
directions between two Controlled Locations at the same time.
In Centralised Traffic Control (CTC), this is accomplished:
in the case of following Rail Traffic, by electrically securing the Signals at Stop,
unless the Block ahead of the Signal is Clear; and
in the case of opposing Rail Traffic, by electrically monitoring the Occupancy of Rail
Traffic and the indication of the Departure Signal at the opposite end of the Section.
Therefore, it would not be possible for the Departure Signals at opposite ends of the
Section to exhibit a Proceed Indication simultaneously.