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Michael R N Dolbear · February 18th 11, 01:50 PM posted to uk.transport.london

d wrote in article
...
On Wed, 16 Feb 2011 19:18:44 +0000
"Clive D. W. Feather" wrote:
More precisely, what I'm saying is that you can't just stick down
some
third rail and say "that's it". You need to modify the existing AC
electrification to be compatible with dual-voltage. And, since the
ECML
is currently not signalled with DC-immune equipment, you'd need to
replace it.

I wonder if its possible to have a signalling system that doesn't use
the
rails at all so avoiding all of these issues. Perhaps using magnetic
detectors or infra red beams or suchlike?

Possible, yes but interference between traction and signalling circuits
can still occur and electricity and magnetism cross-interfere while
infra-red beams would fail with the "wrong sort of rain (or snow)".
Fluidics, hydraulics, fibre-optics are all possible also.

--
Mike D