Re: Signalling Questions in Brisbane?

[signal_spotter@my-deja.com]

In article <395F17B7.5DF27F13@efs.mq.edu.au>,
  Eddie Oliver <eoliver@efs.mq.edu.au> wrote:
> pdwyer wrote:
>
> >
> > It seems to have spread ;) It is not an inherently dangerous
> > practice, the circuit design for the flashing is designed to
> > fail safe, that is the next most restrictive aspect. That's why
> > the Flashing yellows are just above the Red, sequence wise.
>
> Please elucidate. The logic of the above is not clear.
>
> QR is one of the very few systems in the world where the flashing
yellow
> aspect is MORE restrictive than the steady one. In most systems,
because
> of the very argument that you have raised, flashing or pulsating
aspects
> are less restrictive than steady ones - because if the flashing fails,
> the resulting steady aspect is more restrictive and the situation is
> thus failsafe.
>
> Presumably if a QR flashing yellow fails to flash, the signal has to
> default to red. This requires proving that the flashing is operative.
If
> someone else's flashing or pulsating yellow fails to flash/pulsate,
it's
> no big deal.
>
> Eddie Oliver
>
I disagree. The order of aspects in QR (and UK which QR signalling is
99% based upon) from most restrictive to least restrictive is:- Red,
Yellow, Flashing Yellow, Double Yellow, Flashing Double Yellow and
Green. This is how the aspect codes are written in SSI for the signal
memory.

regards Ian
Signal Design Engineer


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