Re: signals in sydney

[Eddie Oliver <eoliver@efs.mq.edu.au>]

Tom Boles has sent excellent graphics of what he was talking about in
the specific context of Gordon.

The first query related to the yellow lights in separate units below
main heads. They are shunt or call-on lights, authorising a train to
proceed past the signal but with no assurance that the track is clear -
i.e. proceed so as to stop short of any obstruction. They give an
assurance that any points are correctly positioned.

The "triangles" are position-light shunting signals, but Tom has
mistakenly identified the top light of the triangle as red rather than
yellow. The indications are

two reds at bottom = stop
single yellow at top = same as "shunt" above.

Eddie Oliver