Re: Bunchrew Level Crossing

In message <eUG9l.11588$st4.476@xxxxxxxxxxxxx>
Charlie Hulme <info@xxxxxxxxxxxxxxxxxxxxxxx> wrote:

MB wrote:

OK, I don't know a huge amount about railway signalling, but how can
the absence of a warning be called "fail-safe"?

It totally depends on the driver knowing the route well enough to
expect a flashing warning, being alert enough to realise it's not
there, and noticing it in time to act accordingly. I don't see how
that's "fail-safe".

But the same applies to any colour-light signal which
may have failed and be showing no light. There is no
such thing as 100$ 'fail safe.'

In this case there is. If a signal is showing NO light, then it must
be assumed to be "at danger". And that is the instruction to drivers,
"if no light is showing at a signal, then treat it as red and stop".

And there are detectors which can detect whether a light is working.

There's a lot of sloppy thinking about this. The French APS system
("Alimentation par sol" = "Feeding from the ground") switches on
traction voltage to segments of rail lying between the running rail.
It was stated that it is "perfectly safe" because "a signal from the
tram switches on the segment below it and a second signal switches it
off". BBC news accepted that. But it is dangerously incompetent. The
"off" transmitter or receiver might fail. This statement was probably
produced by marketing people who did not understand the technical
French and botched together a statement which "sounded good" in
English.

Michael Bell




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