The “moving platform” is a neat theory, but there just seem to be too many things that can go wrong. On an ordinary train platform, if a passenger has trouble with the door (trips and falls, gets a sleeve caught on something, whatever) the crew notice and the train doesn’t move until things are sorted out. If something goes wrong on this tandem train, the only thing to do is bring both trains to a stop– if there’s enough time before the tracks diverge. And don’t even think about pranksters (or worse) with, say, some stout nylon rope.

Anyway, Heinlein wrote “The Roads Must Roll” in 1940. Think of a subway with no trains, just several wide conveyor belts running side-by-side at different speeds. Step from the platform to the slowest belt, then walk across to the next faster one, then the next. Get going as fast as you want, and when you approach your destination stop (or city), reverse the process. Partitions mounted on some belts keep the wind from getting too severe. Oh, and the point of the story was that anyone who can shut down your transportation network has a dangerous amount of power over society.