Re: Beresfield Accident Findings

[eoliver@efs1.efs.mq.edu.au]

In article <354F0117.F67C662F@lisp.com.au>#1/1,
  John MacCallum <johnmac@lisp.com.au> wrote:

> There are hazards in making an emergency application but I can assure
> you that it happens every day on every railway system . Most of the
> time with no ill effects other than the odd skidded wheel .
> I have had occasion to use the emergency position several times and
> have never had any problems .

Thank you for putting a balanced perspective on this.

The original point was that emergency applications USUALLY don't have any very
adverse consequences; nevertheless they can have such consequences, ranging
from skidded wheels through damaged drawgear through (in a worst-case
scenario) derailments. Thus granted that they CAN have adverse or very adverse
consequences, they are to be avoided wherever possible.

What some of us were trying to point out was that installing mechanical trips
on freight trains would (amongst other adverse outcomes) generate unnecessary
emergency applications which COULD have consequences comparable with the
problems which were sought to be solved in the first place. which is one of
several reasons why the rest of the world has generally not used mechanical
trips on freight trains.

Now that we have thrashed that subject to death, can we return to being more
constructive about what viable options - i.e. other than mechanical trips -
are available for automatic train control? The commonest systems around the
world seem to be either single-location type devices like British AWS, or
continuous transmission devices like most forms of cab-signalling where the
information is continuously contained in coded track circuits and the like
(with an immediate fail-safe provision that zero coding is interpreted as the
most restrictive indication).

These things are expensive but effective. They do however depend on fairly
traditional signalling principles (although some have progressive rather than
fixed blocks). Presumably the alleged advantage of GPS-based systems is mainly
that they will work without so much fixed hardware such as track circuits.
Unfortunately at the moment I am not aware of any such systems which are
actually operational in the railway signalling context.

I would be interested in appraisals of such alternatives, and especially as to
what advantages will accrue from GPS-type systems relative to more traditional
ones.

Eddie Oliver

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