The New York subway moves 3.2 million people per day. Taxis and ride share options are together good for about 1 million. Mostly non autonomous and polluting of course. If you triple that with autonomous vehicles that use the road smarter, it sounds doable to match what the subway is moving around. And of course people would be using these for point to point traffic and cars would be able to re-route based on traffic as well.

We'll see how this plays out.