They started installing the new Piccadilly trains on the London metro rail network, they're made by the German company Siemens. They're a lot like the sub surface trains, you can walk freely from carriage to carriage and the train is open plan but still shaped like a Swiss-roll. I thought I should mention some tricks I know of to get about without walking much.
The Bakerloo and Jubilee line come side by side at baker street station, there is a wall between the two platforms but there is a crossing near the end of the platform about 6 meters across. The platforms that are side by side are heading in the same direction. The eastbound Jubilee and Bakerloo platforms are side by side and so are the west bound platforms and they both have a discrete crossing near the end of the platform that often gets unnoticed by tourists, they head to the exit instead and work their way back again.
A similar thing is true of 'Mile End' but there is no wall between the platforms. The central line, Hammersmith line and District line all share the same platform island, they come side by side and changing lines there is as easy as stepping off one train and onto another.