Sometimes a signal pole is observed to carry one signal at normal height and another much higher up; what are those? Or, what are Co-acting Signals?
A co-acting signal is a duplicate signal provided on the same mast as a stop signal, which always shows the same indication as that stop signal. The purpose of such a co-acting signal is to allow a continuous unobstructed view of the signal indication from all positions where a driver might need to observe it, in cases where an overbridge or other obstruction might block the view of a signal from some locations if there were only one instance of the signal provided on the mast. Typically, one of the signals is fixed very high up on a mast and the other one much lower down, so that one or the other is always in view from all positions along the tracks as it is approached. Although theoretically more than two such co-acting signals could be provided on a single pole, this is never seen in practice.
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