Re: signals in sydney

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

> Yes Eddie I'm sorry I forgot to mention that they are used on Main Lines
> when Indicating Shunt such as for changing ends on Platforms
> etc.
> Also have a look at Strathfield Up Main Accept at Auburn. On it you
> will see a small Subsidiary light under the Main Running Signal.
> This light when lit takes you across to the Lidcombe Triangle.
> Also I forgot to say that when used on Main lines as Point
> Indicators they have a Green Light for the Proceed Indication.
> Such as the Dwarf Signals used at Spring Hill.

Several issues here.

1. Sometimes a shunt indication is the only available one to some
particular route past a signal, i.e. there is no running indication to
that route. So although it might effectively SERVE as a sort of turnout
indication, it is still basically a shunt indication in its basic
definition.

The classic case is dead-end signals displaced to one side of a signal
post, which were previously regarded as a separate type of signal.

2. I dispute that the dwarfs at places like Spring Hill are point
indicators. As your binary in another posting showed, point indicators
have arrows instead of non-red lights. The signals at Spring Hill etc
are shunt signals, although again they may be regarded as SERVING as
point indicators in some contexts. 

A closer-to-Sydney example is at Rhodes. There is a dwarf on the down
main just before the points down main - down relief. This is a long way
inside the down home. It is designed to enable shunt movements (e.g. run
round moves). For a train which has passed the down home showing a
proceed indication, this shunt signal is indeed (as you say) effectively
just a reinforcement of the fact that the points are locked for a
particular route - which they had to be for the home signal to clear in
the first place. But for a loco doing a run-round move, it is a genuine
shunt signal.

At Spring Hill there used to be sidings to be shunted, which needed
moves across the single to double line junction without fouling the
single line section to Millthorpe and (after Millthorpe was abolished)
to Polona.

3. Your statement about the green light is an oversimplification. The
green light only shows if the route is set for the main line and the
previous running signal was at full clear. If the previous running
signal showed a restrictive indication or if the turnout route is set,
the dwarf will show yellow with a route indication. However under such
circumstances the "stop short of any obstruction" component is not
required, since the clearing of the previous running signal guarantees
that the route is clear at least to the next running signal.

Sorry to be pedantic, but we might as well get close to the full story
rather than an oversimplified subset.

Eddie