Do we really need High Speed all the way to Cardiff/ Swansea? Since there are almost no local trains west of Didcot (until you reach Bath/ Bristol Parkway) there's not the same bottlenecks that you encounter on the WCML etc.
I'm not convinced that there is a need for high speed rail all the way to Swansea either, which is why I stated "
IF there is to be a phase 3 [of HS3]". I was just laying out all of my envisaged possibilities. I like the idea of bringing West Wales closer to the capital in terms of journey time, but I recognise that the very, very low frequency of trains that would be generated by a high speed line west of Cardiff would fall far short of justifying the line. Such a route would be driven far more by political motivations than economic ones.
As for high speed 3 continuing as far as Cardiff, or as in my example, to somewhere inbetween Severn Tunnel Junction and Newport, the Severn Tunnel is already recognised as a pinch point on capacity in the area, and it is not a great distance from Bristol Parkway, where HS3 trains would otherwise rejoin the GWML, so why not? Other than the fact that crossing the Severn would no doubt represent the greatest part of the capital expenditure on the project, and dramaticaly add to the complexity of the build, admittedly...
Presumably a HS3 would still be stopping at Swindon anyway? Or would people downgrade Swindon to something like Bedwyn gets (with only "non High Speed" services)?
I would assume that there would continue to be a service on the GWML between London Paddington and Bristol, in order to serve the intermediate markets on the route and stopping at all the major stations. Swindon is sufficiently close to London that I don't think that routing HS3 through the middle of Swindon would serve to offer a great deal of additional benefit over the town being served by classic line services, and a parkway station on HS3 for the wider area might be of greater utility to those that live outside of Swindon anyway.
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A new alignment would save time past Tiv PW, but then that would also speed up conventional services too. There definitely needs to be some investment in the SW but I'm not really sure this is the best place to spend it yet.
I'm inclined to agree with all of your comments to be honest: I have answered this thread in the spirit that it was intended, but I do not necessarily see HS3 as being at the top of the list of investment opportunities for the South West region. I will however point out that, based on the proposed opening dates for the two phases of HS2, the earliest date that a first phase of HS3 could open would be around 2040. Under my proposal, HS3 would not reach Devon under phase 2 until closer to 2050. HS3 might be a very palatable option by that time.