I've thought inmediately of Asimov's The Caves of Steel where pedestrians jump from a moving band to another, some slow, some faster. For trains it could be ni

I've thought inmediately of Asimov's The Caves of Steel where pedestrians jump from a moving band to another, some slow, some faster. For trains it could be nice to use small wagons that could change from a train to another, not because of energy saving, but to achieve more speed, avoiding the time needed to change lines. I agree with a previous commenter that trusting passengers to behave correctly is looking for problems.