On Sat, 15 Sep 2007 13:27:28 -0700, Mizter T wrote:

Thirdly and critically there's always the issue of paving and
conflicts. I think that trains from WCML slow lines to the WLL need to
cross the WCML fast lines on a flat junction, so any such moves block
up the fast lines.

They don't. There is a (very slow) diveunder.

Northbound ex-WLL trains do have to cross the southbound line towards
Euston, though.