British accident track layout

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

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