Shanghai is massive but that's just the sheer size of its population. It's the most populous city in the world on some measures; they've planning for 30 billion by 2030. It's built much denser than most US cities, which means it's much more walkable, and the subway network also makes it much more practical to travel by train because it means you don't need a car at the other end.

You have to start with getting rid of parking minimums and "green space" and building dense, walkable cities. Once you have those it makes a lot more sense to connect them with trains or similar.