In Stockholm we were a bit late to the party and dug our tunnels bigger, our teeny wheeny network has about 50% above ground stations and most new development is underground since it's easier to DnD (drill and dynamite) through a neighborhood than getting people to move.
Sadly we combine the worst of two worlds, in the summer the train takes on heat though radiation, but since track is tunneled they can't run AC which would heat up the tunnels (we haven't developed on/off switches in Sweden yet).
We only have 65 miles of track compared to Londons 225 but ours is uniquely cool by being bedrock excavation instead of dig & cover.
Sadly we combine the worst of two worlds, in the summer the train takes on heat though radiation, but since track is tunneled they can't run AC which would heat up the tunnels (we haven't developed on/off switches in Sweden yet).
We only have 65 miles of track compared to Londons 225 but ours is uniquely cool by being bedrock excavation instead of dig & cover.