Unfortunately only about 45% of London's rail system is underground, so the size of the underground metro would be about half the total length of Moscow's. In any case, I think enough interest has been gathered to open an OoC, so I'll likely be doing that later tonight. When I do I'll be tagging everyone to make sure you're all still onboard. Once we're in there, we'll be able to hash things out a bit more in depth. Honestly though, I'm currently debating saying all the lines are underground for London's metro system in this AU. It would make things much less complex.