Why not extend the OHLE to Shepherd's Bush?

The Hammersmith & City Line's signalling needs replacing or immunising against electrical interference from the OHLE where the WLL passes under it. It wasn't thought worth the effort, especially as the station was built pre-Metronet collapse and resignalling of the SSL was imminent.

Yes, but you'd probably need another substation for the third rail and the electrical isolation issues on the dual electrified sections would be interesting, to say the least. You'd also run into the issue of where freight trains switch over - especially those headed for the WCML.

So: expensive, introduces new sticky operational issues and saves you a minute or two in journey time tops.

The main reason why the third rail wasnt extended was down to money first of all and the H&C crossing it. There is no height to have overheads under this bridge. it either require the H&C to raise or the WLL to lower unlikely due to cost on both of them. With regard having the third rail to Willesden this was ruled out in 1995 when the NLL was closed and the third rail lifted completley. Also when it is not possible to extend third rail to areas which currently dont have it and any new sections of electrification must be overhead wires. Also if you remove the change over point at North Pole where would the Southern service change?

As for the change at North pole Junction, this was done long before their was a plan to open a station at Shepherds Bush. It was discussed as to whether to move the change over point to Shepherds Bush, but as well as the cost it would not save any time in the train service. So would really be a waste of time.

Does that mean that class 378s will also take longer to change than the class 313s?

I see.

I don't get it; surely one of the reasons always given against re-building a station at North Pole is that it would reduce capacity on the line; and yet the trains have to stop for a station-stop length of time for the power switch anyway.

The 377's can change power source while moving.

They have done changeovers on the move in the past, but if such an attempted changeover fails then chances are the train won't be able to stop safely within the changeover zone (apparently). Hence the 1+ minute pause near North Pole Junction, although I wouldn't be surprised if the above could be dealt with by doing so at a low speed.

They're designed for it and other stocks aren't but can be bodged?

Are you sure about this? I was under the impression that the ban only applied to new electrification projects and not extensions to existing ones - hence why MerseyTravel have been going on about Extending the 3rd rail to Wrexham in recent months again.

@ electra: yes, extensions are allowed (also, protected 3rd-rail is still allowed for new projects)

@ norbitonflyer: but did the ECS E*s change over on the WLL without stopping, or was that only the ones in service at Fawkham and Ashford-ish?

Actually that's a really good point. The only ones that needed to change over were the GNER subleased ones, on their way between OOC and Kings Cross via the NLL.

I meant the way they switched power on the move near Folkestone.

Basically; if the issue of dual-voltage trains having to stop in order to change sources was solved with the advent of the eurostars, I really can't understand why this technological breakthrough did not reach to subsequent trains.