Michael Bell wrote:
It is a fairly obvious feature of railways south of the river that
many run at roof level.

I once got into correspondence with somebody who said "It is the
long-term objective to put these routes underground".

I felt like asking "Are you on the same planet as me? The cost
would be astronomical, and for what benefit?", but I let it drop.

Is this REALLY a serious proposition?

I would say, with a high level of confidence, no! As you point out, the
cost would be absolutely astronomical. Some could be recouped by
developing the land above the newly-submerged railway, but the
disruption would be ridiculous.

I think TPTB have their sights set on other long-term objectives - such
as making the railways work properly - first.

Perhaps the person you were talking to was thinking of replication of
some overground routes with tunnelled ones, such as for Crossrail 2
which would replicate services between Clapham Junction and Victoria
using a tunnel.


--
Dave Arquati
Imperial College, SW7
www.alwaystouchout.com - Transport projects in London