Its not that simple though. If you want to serve intermediate towns between Birmingham and London not only do you extend the route and journey times, but you have to route the line through built up areas and build stations central enough to be attractive - considerably increasing the cost of the line.
You suggest this needs to be done because HS2 will have too much spare capacity, which seems highly unlikely, yet you propose something which leaves the WCML underutilised instead. As this would cost a lot more to build, sacrifice long-distance journey times and damages the business case for further extensions i cant see the point.
Even if there was a lot of spare capacity, HS2 opens up far more possibilities
to use it than the WCML does.
HS2 should be built to suit this countries characteristics, geography and journey patterns - capacity constraints (especially around London,
Birmingham and Manchester) and loading gauge make a dedicated line both viable and neccesary.
Chris
1. The extension in the route's length is not significant, fast trains to Birmingham and Manchester/Leeds will not notice the difference in journey times. One might as well argue the case for building the line as a completely straight line between London and Birmingham.
2. Building the line through Milton Keynes, Northampton, Rugby and Coventry would require by my reckoning only an extension of the Chiltern tunnel and three additional short stretches of tunnel (at Milton Keynes, Northampton and Rugby)
This with the Rugby and Coventry stations built adjacent to or integrated into the existing stations and the new Milton Keynes station built inside the "grid pattern" of the city. (Hard to really say centre as MK is rather decentralised compared to many cities).
These tunnels come to a grand total of roughly 12 route kilometres.
The extension to the Chiltern tunnel is far harder to calculate due to the fact that it keeps changing in the current HS2 plans and the fact that the route is apparently being specced to quite conservative gradient requirements. (2.5% max gradient compared to the 4.0% on atleast one German HS route, you might even be able to cross the chilterns with no tunnels at all using the latter specification, although the NIMBYs would not like the resultant viaducts, embankments and cuttings).
Lets say 15 route kilometres of extra tunnel, using the costs published by HS2 Ltd
here this comes to roughly £420m pounds.
Well add in additional costs such as inflation and viaducts or whatever to traverse the area around the Rugby station as in my rough proposal
here and come up with a rough cost increase estimate of roughly a billion pounds including the extra stations (which would be simple two platform face, two through road affairs, probably with the through roads on the
outside and a single island platform).
Even so, the cost of the extra trackage and tunneling pales in comparison with the overall cost of the project.
Now to the "it reduces capacity argument".
There is no shortage of capacity on HS2, unless you really think we are going to be abel to find tens of thousands of passengers flowing each way every hour. (Even during rush hour this is pushing it).
400m Double Deck trains (taking maximum advantage of the infrastructure) have a capacity of over 1200 seats a peice, therefore I cannot see any reasonable reason to assume more than 2tph to either Birmingham, Leeds or Mancehster would required, with 2tph also proving more than enough for any reasonable expansion of the network to Scotland if the more logical route via Newcastle was taken (the trains can all serve Newcastle, Edinburgh and Glasgow in that case).
The possibility of stopping and semi fast services (serving the "stopping stations" on the phase 2 sections of track) becomes neccesary to ever have a hope of using up the 18tph available, especially if the sensible step of requiring CC trains to couple into 400m formations prior to travelling over the core section is taken. (And before anyone complains about that affecting journey times, journey times are so dismal to the places likely to recieve CC trains long-term as to make the time taken to couple them into said formations almost trivial in comparison to the savings gained by the use of the line).
As to the charge that doing this would leave the WCML "underutilised"...
The more paths freeed on the WCML the better, as those paths will be useful for improved intermodal and London MIdland services, as well as the remaining Virgin services which will provide a measure of "economy intercity" service to secondary stations on the route.
Further extensions north of Leeds or maybe Newcastle have pretty poor economic value anyway unless value is ascribed to eliminating the major domestic air axis.
Either way such extensions would at most require 2tph over the core section if done correctly (via
Newcastle rather than any ill concieved attempt to shorten the journey by a few tens of kilometres (and the required trackage by even less than that due to the lack of a readymade HS route to Edinburgh as a consequence of reaching Glasgow) by cutting straight through the middle of the Peak district and leaving the North East to rot).
The fact remains that the Shinkansen model is far more suitable than the TGV model, and while the extreme Shinkansen model is probably not the best thing for us to adopt, it provides a far better fit than the TGV model.
EDIT:
Note my route proposal is
extremely unpolished, and while I was reviewing it to gain tunnel lengths I realised I could divert the line via a route through the Chilterns closer to Tring and probably shorten the tunnel requirements considerably, I will have to recalculate once I have worked out if that is feasible.
