Bi-Directional SignallingSignalling which permits trains to be signalled normally in either direction on a Running Line. where the signalling in the opposite direction to
normal traffic provides for a lower speed and/or capacity than that in the
normal directionOn a line for which the signalling is provided for one direction only, Normal applies to the signalled direction. On a Bi-Directional Line, Normal applies to th..., and bi-directional operation is only required in connection
with Possessions or emergencies affecting the other line(s).