Re: British accident track layout

[Bob <alco@acay.com.au>]

You may also be interested to look at:
http://freespace.virgin.net/g.mayo/sn109.html
Cheers
Bob

Eddie Oliver wrote:

> Despite the aggressive posting from someone who says that we either
> don't know what we're talking about or would know to keep quiet till the
> inquiry is finished, let's just get as close as we can to the facts (as
> distinct from the interpretations).
>
> The layout, as supplied to an international signalling mailing list by a
> very reliable source, is complicated, but the RELEVANT parts of it are
> thus:
>
>   -----------------*--------------
>                  B/
>     -----------*-*-----*------<H---
>              A/       /D
>     --T>-----*-*-----/
>                C\
>     -------------*-----------------
>
> Paddington is at the left-hand end. There are also many other tracks and
> many other crossovers irrelevant to the accident.
>
> The train T was the one which allegedly passed the signal at stop. That
> signal was allegedly held at stop in anticipation that after the HST (H
> on the diagram) had passed, crossovers A and B would be reversed for the
> train T to proceed onto the line at the top of the diagram.
>
> Crossovers A and C were both normal (to reverse C would send the train
> into a potential accident on the bottom line of the diagram).
>
> Thus once T passed the signal at stop and kept on going, it would
> ultimately end up at the points D, there being no catchpoints. That is
> where it did end up - colliding with the train H.
>
> The distance between the signal and the points D was greater than the
> overlap distance which is required to exist beyond a signal at stop (to
> protect against braking errors and the like). Thus from a signal design
> point of view, the design was consistent with British overlap principles
> to protect against driving errors of the braking variety; there was just
> no protection against the train passing the signal at stop and keeping
> on going.
>
> This of course makes no assumptions about whether or not the signal was
> in fact passed at stop. We are simply at this stage discussing how IF
> the signal was passed at stop, it would result in a collision at the
> points D.
>
> If anyone wants to see a pretty complete ASCII representation of the
> complete track layout, look for a posting by Clive Feather on the
> newsgroup uk.railway at about 0100 Australian eastern time Friday
> morning.
>
> Eddie Oliver