Re: [WA] Zanthus collision 18 Aug

[david <david@nmit.vic.edu.au>]

See my text further in...

Eddie Oliver wrote:

> Maurie Daly wrote:
>
> >
> > On NSW CTC and most  (all ??) other systems the arrival signals are controlled
> > both by the track ccts of both the main and loop , and also by detectors in
> > the point machine which senses where the blades of the points are .
> > Approach locking is applied directly to the point machine so that it cant be
> > changed whilst a train is approaching or a train is over it.
> > Any half decent system simply woudnt have let the points be reversed whilst a
> > train was sitting in the loop.
>
> Huh? In that case, how do you ever get a train out of the loop, or do a
> shunting movement, or do a three-train cross? Probably you didn't really
> mean that last sentence in quite the way it came out.
>
> You seem to be constructing a rather circular argument here, viz. if the
> area is fully track-circuited, the signals will be controlled by the
> track circuits. Obviously usually true, since that is a prime purpose of
> the track circuits!
>
> However you have to consider two other situations:
>
> 1. Only some parts of the area are track-circuited, e.g. an older-style
> NSW automatic crossing loop where the main line is track-circuited
> between the respective landmarks but the loop is typically not
> track-circuited.
>
> 2. There are no track circuits at all, or they cover only the area
> immediately around the points.
>
> The Nullarbor is train-order working, and the track circuits (if any)
> are extremely localised to the vicinity of the points. There are no
> longer-distance track circuits by which approach locking can be
> effected. You can't have conditional approach-locking if you don't have
> a way of detecting when a train is approaching.
>
> That is why some systems - but until now, evidently not on the Nullarbor
> - have a compulsory timing mechanism so that points cannot be reversed
> until a few minutes have elapsed, which gives an opportunity for any
> approaching train to be brought to a stand and for second thoughts by
> the person who plans to move the points.
>
> Eddie Oliver

According the the first post, the accident was part due to the points been changed
to reverse by the train in the loop. And the system locked  him long enough  to
cause the crash
- which is sort of what is been discussed now - the points did lock the settings !

What I wouild like to know is the train in the loop , why did they set for the loop,
or didn't they know and were trying to set for the  main ? Surly they knew they were
crossing !
and ideas as to the  actual sequence that happended ?

Regards,
David Head