In article ,
Tom Anderson writes
What's the loading gauge of the subsurface lines?

Varies.

I read somewhere that
it's the same as National Rail (don't know which);

I don't think so - I believe that A60/62 stock is too wide for parts of
the NR network.

this must be true for
some of it, since there were plans to run mainline services over bits of
it (Liverpool Street to, er, somewhere along the north side),

You might be able to get some NR stock that way, but there will be
various issues to resolve. In particular, it tends to be longer and will
therefore have problems on curves.

AIUI, _no_ current subsurface stock can get everywhere).

I can't think of anywhere that C stock isn't allowed to go. There's a
limit of 4 cars when in service on the ELL, but that's all.

What is the
least common denominator gauge like? Presumably, this is what the proposed
single subsurface stock will be built to; are they going to have to be
titchy? Are they going to regauge bits of the network instead?

D stock isn't any wider than C stock; it's limited where it can go
because:
* some stations (like Bayswater) can't fit 6*D though they can fit 6*C;
* the suspension has been stiffened and it's therefore only allowed on
track maintained appropriately (which, off-Line, means Acton Town to
Northfields Depot).

My understanding is that the new stock will be built to C/D loading
gauge, running in different lengths: 4 cars for the ELL, 6 cars for
Circle, H&C, and Wimbleware services, 7 cars for the District via Tower
Hill, and 8 cars for the Metropolitan.

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