Re: Question re: overlap

[signal_spotter@my-deja.com]

In article <394D9E77.310224BA@ozemail.com.au>,
  trainman@ozemail.com.au wrote:
> I have a question, aimed mainly at Ian:
>
> On the Y-Link (Harris Park - Merrylands), the home signal is the only
protection
> for the points - there is only one stop signal, being the home, and no
> catchpoints.  If a train was to be approaching Merrylands from Harris
Park at
> track speed (50), and pass the home at stop, it would probably go far
enough to
> foul the down old south.    Why is this protection set up this way?
>
> --
> 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.
>
>

David,

I just remembered that we do have a copy of Granville SSI data here in
the office. So anyway I downloaded it into the SSI Simulator (our
computer train simulator which we use to test SSI schemes before
they're installed on site) and had a bit of a play with it to test your
query. The Signal that reads from Harris Park to Merrylands along the
South West Outer is GE424. It reads up to an Automatic Signal called
WO13.9 and the next signal is GE289, the home signal which protects the
points in question. The points are a single ended set (ie no
catchpoint) called 756. Anyway the 'normal' lie of the points is from
the Dn Sth Main to the South West Outer. Routes along the Down Sth Main
actually throw them 'reverse'. So those points must be far enough past
GE289 (beyond WO13.9 overlap) or else WO13.9 would have been made
a 'controlled' signal and would set, lock and detect 756 normal. I
couldn't find my GE25 braking curves (the ones we use to determine trip
braking distance based on gradient and speed) to confirm this but the
guy who designed it would have definately used them. Incidentally the
route that reads along the Dn South Main (in the down direction) from
signal GE277 does set, lock and detect 756 reverse so it's overlap must
go past them. So don't worry, it's safe. Trust us, we know what we're
doing :-) nyuk, nyuk, nyuk

regards Ian
Signal Design Engineer


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