At least in NSW, if the top Green is on, you know the track is clear to the
next signal. If the Top light is Red, you know you have to stop. If the top
light is yellow, you have a turnout. Simple. The bottom lights are there to
tell the driver if there is a signal at stop within the next 2 or 3 signals.
I am not sure what the present rules are on passing failed signals. Maybe
Craig can fill us in, but I will look at it logically:
Top Green only: Section is clear - safe to proceed to next signal, being
aware that it may be at stop.
Top Yellow only: Section is clear, route set for turnout - safe to proceed
through turnout at turnout speed (usually 25 km/h), being aware that next
signal may be at stop.
Top Red only: Stop. Follow instructions for passing signals at stop.
(Usually involves ringing signal box in controlled areas)
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Bottom Green only: The only indication that this could mean is that the track
is fully clear for the next 2 signals.
Bottom Yellow only: Could be either 2 signals until a stop indication, or, a
turnout. Proceed at turnout speed until route ascertained.
Bottom Red only: Could be either 1 signal until a stop indication, or the
signal could be at stop. This can usually be ascertained by the position of
the trip - up=stop, down=clear. I would treat the signal as a stop signal and
follow the instructions for passing a signal at stop if unsure.
The defective signal then SHOULD be reported on a trackwatch form, and also to
the signalbox. Most drivers don't do this, because they can be breath tested
by the police for doing so.
I think this is a much better system of signalling than Victoria.
-- David Johnson - Rail Services Authority trainman@ozemail.com.au trainman@railpage.org.au http://www.ozemail.com.au/~trainman