On May 22, 10:48*am, 77002 wrote:

Your Euston, TCR, Waterloo tunnel is optimistic. *The WCML descends
steeply down Camden Bank, your tunnel would have pass below the H&C.
I am not saying this is not doable. *But, a survey might throw up some
interesting challenges. *That said, bits of this route already exist.
During WW2 a start was made on a main line gauge tube paralleling the
Northern line,

Details? First I've heard of such a scheme. There was the deep level
express lines, tube gauge tunnels bypassing Northern line stations
with the idea of introducing skip-stop type working, but that was a
pre-war plan and definitely not main line sized.

Robin