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Arthur Figgis · August 13th 03, 09:13 PM posted to uk.transport.london

As 12 Aug 2003 01:19:59 -0700 appeared fresh and rosy-fingered,
(Boltar) wrote:

[third rail]

Thats only because currently (no pun intended) high speed lines use overhead
because they use high voltage, they're not intrinsically required like they
are on a tramway (to keep the electricity well out of the way of people and
vehicles).

FWIW, you don't have to have overhead lines for electric trams -
London had its conduit, and various places have had stud contact,
including parts of the brand new tramway in Bordeaux.

If a high power 3rd rail design could be devised (which I'm sure
would look substaintially different to "traditional" 3rd rail) then there is
no reason they couldn't use that and perhaps it might have avoided the problem
that the Eurostar had last year where freezing sea spray got onto the overhead
lines and stopped all the trains.

There is the problem of picking up the power at high speeds. Once you
start getting over 160km/h-ish the collector shoes can bounce around
too much. I suppose you could try some sort of pantograph running on a
low level wire, but I'm not sure that would achieve anything.

I can't help thinking if third rail was such a good idea someone else
would have installed it by now (add the Berlin and Hamburg S-bahns to
my list in the other post. They are metro-like, but pretty extensive.)

Why re-invent the wheel, and introduce an incompatible new system at
huge expense? Internationally 25kV 50 Hz is effectively standard
nowadays, the equipment is available off the shelf (and once we shoot
all the Daily Mail readers, sorry, I mean sort out the important
political issues, we might even be able to get standard foreign trains
running through to Britain on it).

--
Arthur Figgis