Peter Masson wrote:
Airtrack, as currently planned, will terminate at T5. 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.

I wondered about corrosion of rails etc in the tunnels?

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

So that starts to make the case for a change at Staines...

Theo