Re: Signalling Questions in Brisbane?

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

signal_spotter@my-deja.com wrote:

> 
> So why has QR taken a system  that they're 99% familiar with and added
> the complexity of a BR system that they're not familiar  with  to it.

I don't believe they have. It is only the British system which is so
complex, not the QR one.

The heart of the matter is not the QR use of flashing yellow as a "no
overlap" indication (which is straightforward enough, apart from its
breach of the normal "flashing is less restrictive" principle). Rather,
it is the British fetish for approach-releasing which is the
complexity-generator.

The British equivalent of QR flashing yellow is basically
approach-release to yellow - in other words, if a driver finds a signal
clearing to yellow only just in front of him, this is supposed to tell
him that he may only have a restricted-overlap situation. Of course it
then has two immediate disadvantages - viz (a) the risk that the driver
will falsely ASSUME that it will clear, and thus SPAD; and (b) the lack
of differentiation between a genuine "normal" clearance to yellow and
the conditional clearance.

Similarly the British flashing yellow is required to indicate that the
junction signal ahead is being held at stop, but will clear when the
train approaches it. This happens when the route set at the junction is
of substantially lower speed than the main route(s). Thus the flashing
yellow is, in effect, a primitive but complex form of advance route
indication.

Of course QR now has its own sophistications to achieve similar
purposes, e.g. dynamic speed indicators.
I'd choose the QR system over the BR one by a wide margin.

Eddie