"CharlesPottins" wrote in message
...
I thought the reason underground tube lines were less common south of the
river
was the number of underground streams?
(Please don't tell me this was an urban myth!)
It might be less of a problem with more modern tunneling techniques and
deeper
lines, but the cost would surely not be justified by any useful purpose?
Don't know about you but I prefer riding at roof level - you can look out
of
the window, and get some ventilation.
Regarding consideration at the time of World War II, there might have been
an
obvious reason then for wanting to put everything underground.

According to a couple of TV programs I saw recently the problem is the soil
through which the tunnels would have to be excavated. Apparently it had no
structural integrity and would crumble too easily compared with London Clay
which stays in place long enough for the tunnel segments to be fixed in
place.
Cheerz,
Baz
Happy New Year !!