On Sun, 20 Apr 2008, Peter Masson wrote:

"Theo Markettos" wrote

Airtrack's going to have to have a voltage changeover point somewhere.
The council have suggested it should be at T5 for environmental
reasons. I don't see a problem with them saying that, if it is just a
proposal. There may well be technical, operational or other reasons
which means third rail is impractical or costly on that stretch but
that's for the developers to make a case for.

Airtrack, as currently planned, will terminate at T5.

Yes. Which means there's no reason for any OHLE at all.

It has been stated that the tunnel approach to the station, and the
Airtrack platforms at T5 will have to be 25kV OHLE, though I haven't
seen an explanation of why this is so.

Which would be nice to see, because that sounds like a totally bonkers
idea.

This being the case, there will have to be a voltage change somewhere
between Staines and T5. It would seem to make sense, in the longer term,
for Airtrack and Heathrow Express and/or Crossrail to link up, with
through running, which of course would require dual-voltage stock and a
voltage change somewhere.

In which case, since the stock will have to be dual-voltage anyway, why
bother making the Airtrack bit OHLE? Why not have the change at T5, thus
allowing third-rail trains to run from the south into T5 too?

An intermediate possibility is for HEx to be extended to Staines.

This is the only reason i can think of for doing it. Even then, it means
sacrificing the ability to run third-rail stock into T5 for this mythical
future option. Is it the case that existing stock won't be allowed anyway,
for safety or ABB [1] reasons?

tom

[1] Arbitrary BAA bull****

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