A co-acting signal is a duplicate signal to the main signal located in the same location, usually on the other side of the track or lower or higher than the main signal. Its purpose is to give a better sight line when the main signal may not always be visible due to obstruction.
Depending on the height of the signal, its aspects may be in a different order to the main signal. However, it should always display the same aspect as the main signal. Any difference is considered an invalid aspect and the signal in rear will show red on modern interlockings - sometimes yellow in older interlockings.
Last edited by GeoffM on 15/09/2016 at 03:01