"asdf" wrote in message

On Fri, 19 Aug 2005 14:19:45 +0200, "Alan \(in Brussels\)"
wrote:

Yes and no, because although those are indeed examples of what the
OP of the text meant, what he actually wrote (as he clarified
subsequently) referred to the construction of tunnels *to replace*
surface or elevated lines.

The Circle line through Barbican almost fits this description - it was
in open cutting before being rebuilt in tunnel when the Barbican
Centre was built.

Did they lower the level of the tracks when they built the Barbican
Centre? Or did they just use the valuable air space over the tracks in
the cutting? I assumed it was the latter. In which case, there are
many other examples of such exploitation of air rights, and not just on
the Underground.

The most recent, of course, is the tunnel fiasco at Gerard's Cross,
where the Chiltern line now runs through a (fragile) tunnel, without
changing its level in the slightest. Other fairly recent examples of
building over formerly open lines include Fulham Broadway, Gloucester
Road and perhaps South Ken to come.