In message
-septem
ber.org, at 10:28:37 on Sun, 24 May 2015, Recliner
remarked:
While the Piccadilly Line is constrained to being under roads through
most of Central London it breaks away just south of Russell Square and
all the way to Kings Cross. The line is in fact a merger of routes: from
Finsbury Park to Holborn and Hammersmith to Piccadilly, joined with a
third stretch from Piccadilly Circus to Holborn.

That was the legal basis, but were the tunnels themselves constructed as
though for three railways that had already been combined before
construction started?

It think it was constructed as one line, but maybe the two main sections
had previously gained Parliamentary approval with different rules about
being constrained to "under roads" or not.

Was the constraint about lines not running under buildings a legal
limitation, or a prudent decision by the tunnellers to minimise the chances
of being subsequently sued by building owners over cracks that developed
once the trains were running?

Whichever one dominated the decision, it clearly made differently for
the two halves.
--
Roland Perry