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?

Thanks,
tom

--
forget everything from school -- you are programmer