Re: signal question, Wollongong...

Rob Ferguson wrote:
> Although it would be a logical approach, I'm not sure about
> eliminating all confusion. The green over yellow would be so similar
> to yellow over green  that it may well raise 'human factors' issues.

Yes. A feature of the NSW system (unlike, say, the Victorian one) is 
that the inversion of an aspect is not a valid aspect (unless both 
lights are the same, of course). Thus even if someone is vertically 
dyslexic, they don't get a different indication from that intended.

> How about if the signal at the turnout displayed a 'plain line'
> indication no matter what the route (e.g. G/G G/Y G/R etc), but with a
> feather indicator to show if the diverging route was to be taken. The
> signal in the rear could then show yellow over yellow, and the one in
> the rear of that could show green over yellow, with the exception of
> high speed turnouts where these 'reduce speed' aspects would not be
> necessary?

Changing from one system to the other would never pass safety 
validation. During a transition phase, there would be some signals where 
a particular combination had one meaning and others where it had a 
different meaning. Moreover someone could subconsciously revert to a 
previous meaning.

The closest to this in practice is when someone comes off Victorian 
indications where green over red means full clear, onto the NSW 
double-light system where it means caution. Fortunately no one has to 
work on both systems in one shift, although many Junee crews (for 
instance) would do so on different shifts.