Especially considering the fact that the HSTs would run under the wires from Paddington to Newbury. Would make a lot more environmental and economical sense if EDMUs are used instead of the diesel-only HSTs.
its the big paradox isnt it?
Operationally and environmentally everyone prefers all-electric and full-route electrification
But Bi-modes will be cleaner, even if not cheaper, on part-electrified routes
And if you build enough of them you can use the differential cost between their diesel and electric modes as firm evidence for electrification decisions by pointing out that certain routes can be electrified without the additional expense of new stock..
Either IEP is a full HST replacement plan or it isn't. Talk of keeping HSTs for some routes can only be a stop-gap unless they're intended to be rebuilt for DDA compliance.
As I understand it, some IC125s are intended to be rebuilt for DDA compliance, and have been since wires to Cardiff were announced I think. Once that amount of work has been done to them, I doubt you'd want to be scrapping them just 5 years after the 2020 DDA deadline. In a way though, even though I think that means any life-extended mark 3s will work through to at least 2030, if not 2035, I still think of the IC125 life-extension as a stop-gap. 2020 to 2035 is an extra 15 years of diesel, but new diesels (IEP) would come with at a cost of at least 30 extra years of diesel. In theroy yes, bi-modes (which several of us on here argree should be existing 22xs not new trains) will be cleaner than all-diesel. However, there are two points that combine to make that not so. First, the existing diesels can be phased out by 2040, if we have IEP diesels they will delay completion of electrification and completion of removal of diesel LDPE stock beyond 2050, thus extra years of emmisions. Secondly, one of the little devils in the details of the daft Swansea electrification "lack of business case" report was that IEP EMUs would have no additional journey time benifits over an IEP bi-mode on diesel power. They say this is down to the curvature of the line not permitting higher speeds. Hang on a miniute there DafT, the journey time improvments claimed elsewhere are not, apparently, the result of higher linespeeds. The faster speeds gained by electrification are the result of quicker acceleration, therefore curvature limiting linespeed matters not.
So, if IEP diesel is no quicker than IEP electric, they must have made another of the mistakes of the Voyager, sticking in stupidly powerful diesel engines to allow it to accelerate like an EMU at the cost of fuel ecconomy. That means, while the bi-mode would be cleaner under the wires than an Intercity 125, it'd drink far more fuel than their more sluggish predessors once the wires run out. That, and the number 2 complaint about Voyagers, their noisy/uncomfortable underfloor engines, are the reasons why PAD - Plymouth/Penzance, with so much more of the journey away from the wires than under them, should remain IC125 operated until the wires strech far enough.
Being about half under the wires and half away, the Cotswolds line route is in ideal bi-mode country, so stick some 22xs on that. Cheltenham and Swansea are a long way under the wires with a relativly short section beyond, making them ideal candidates to be included in the initial electrification (and they help each other by Cheltenham providing the Severn Tunnel diversionary route, if the Chelteham - Cardiff services are electrified as part of the ValleyLines network).
