Re: [NSW] Olympic Park/City Railway Signalling Question

[signal_spotter@my-deja.com]

In article <39E98CAD.1EE76F9B@ozemail.com.au>,
  trainman@ozemail.com.au wrote:
> Chris Downs wrote:
>
> > One of the operational limitations at Olympic Park was the delay
between a
> > service departing either platforms 1/2 or 3/4 and the following
train
> > entering the same platform.  It appears that the signal permitting
entry to
> > the platform did not clear to caution until the preceding train had
cleared
> > the tunnel portal or thereabouts some 200m beyond the station.  The
> > practical implication of this was that even when trains were queued
it was
> > about 90 seconds usual minimum from the 1st train starting until
the 2nd
> > train stopped, quite a chunk out of 4 minute headways.

Yes according to the SSI data, 825(M)A route won't clear to a Low Speed
until 831AT is clear.
> >
> > When reading David R. Keenan's and Howard R. Clark's "FIRST STOP
CENTRAL"
> > they refer to the later version of speed control signalling used in
most of
> > the City Railway (except the St James - Central leg which uses the
earlier
> > version).  The following statement is made (page 67):
> > "At peak periods it is possible for a following train to closely
approach a
> > station while the previous train is still in the platform.  In some
cases
> > when this close headway is in operation, the platform entering
signal can
> > clear before a preceding train is completely out of the station in
order to
> > allow the entry of the following train without delay."

I have to question the integrity of this book when it comes to
describing railway signalling matters. Have the authors merely observed
this in action whilst sitting on the platform or have they interviewed
signalling designers as to how it was designed. Anyway the signal
leading into the platform could only clear (to a Low Speed) if the
train was clearly past the following signal. And normally the track
past that signal would have to be clear too but with about 3
Intermediate trainstops this requirement could be reduced, in the name
of headway. There would be no cases where a train could follow the tail
end of another train into the platform.
>
> I also have a question.  What was the signal indication given?  If it
was giving
> a low speed indication (Red over Red over Green), and there was a
train between
> that signal and the next, it would be a signal irregularity.

Agree it would be a signalling irregularity but to get a Low Speed on
825 signal requires all the tracks up to the next signal clear plus the
overlap track (831AT) clear.

>  The only possible
> indication would be a calling on signal (Red over Red over CO), but
the signals
> before the platforms are all automatics, and Calling On signals must
be fitted
> to Home signals (and variations thereof).  Also, a Calling On signal
is supposed
> to have the trip up, which defeats the purpose of clearing it.  Does
anyone know
> the full details?

I've checked how the SSI data was written (I have a copy) however it
was written by RSA and the version may have changed from what I have to
what is installed. Anyway the signals leading into the platforms will
show a caution if the tracks a clear up to the next signal plus the
next track past the next signal is clear. There is no Low speed or Call
On on those signals, just a Low Speed on the home in the rear.

regards Ian
Signal Design Engineer

>
> --
> David Johnson
> trainman@ozemail.com.au
> http://www.ozemail.com.au/~trainman/
> ------------------------------------
> These comments are made in a private
> capacity and do not represent the
> official view of State Rail.
> C.O.W.S. Page 11.
>
>


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