If it has a red light, there will be a preceding signal with a yellow light. If that is yellow, the signal will be red. Hence the need to slow down. Of course, it may have cleared in the meantime. Signal locations are based on braking distances. If there is a sighting issue, a "repeater" is placed before the signal giving a clear/caution indication - the the signals at the western end of the cutting outside Heuston for examples.
Cue locking of thread for being "too technical".
LC
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