Tom Anderson wrote:
I have been told that the cost of making new tube tunnels depends on
their size, with Crossrail-style NR-standard tunnels being more
expensive than classic LU-style tube tunnels. Is that true? If so,
why, and how big is the difference?

I can see why it might be greater - there's more mass to shift, more
surface to line - but not massively greater. If it's only a bit more
expensive, wouldn't it have made sense to build the underground to be
compatible with the rest of the network, as, AIUI, in Tokyo?

At the time the tube lines were envisaged I don't think there was any idea
of getting them anywhere near the main lines.

The sub-surface lines can accomodate main line gauge stock although it does
get a bit tight in places with modern stock. In 1982 a test run was carried
out with two battery locos and a BR Mk2 coach. It got round the Circle
although it did touch in a couple of places. This was in preparation for
passenger workings using ex-Met loco No12 Sarah Siddons. In the event these
workings were limited to the Met Main to Amersham and Uxbridge. Sorry can't
be certain where the southern reversal point was, but I think Wembley Park.

Until 1939 there was a through working between Ealing Broadway and Southend
using London Tilbury & Southend Railway rolling stock. Haulage from Ealing
to Barking was by electric loco and from there by LTS steam loco. Prior to
WW1 a number of main line companies provided services over the Metropolitan
and Metropolitan District Railways.