On Mon, 1 Mar 2010 08:14:26 -0000, "Graham Harrison"
wrote:

All of which suggests the answer to my question of how much spare capacity
does Marylebone actually have is "not a lot".


Some Chiltern trains could run into Paddington rather than Marylebone.
A half hourly service to Birmingham would only need two platforms.

There would be a powerful case for making Paddington the second London
terminus (after Euston) for 125 mph trains to Birmingham, given
Paddington's Crossrail connections. And of course Crossrail should
free up some terminal platform capacity at Paddington.

This would also have the advantage of giving a very straight alignment
between Old Oak Common and Northolt Junction, saving several minutes
over the slower route between Northolt Junction and Marylebone.

125 mph running should be possible from Old Oak Common to at least
Denham Golf Club without any major changes in alignment.