> Even if you had a full-autonomous only Interstate where each car could be fully loaded and ride bumper-bumper at over 100kph, it wouldn't even begin reach the carrying capacity of currently existing fully autonomous subways systems like those in Singapore.

This is a poor comparison because cars on highways don't serve at all the same needs as subways in one of the densely populated areas in the world. I'm sure I could construct comparisons where airplanes fail, but a fleet of bicycles succeed(or vice versa), but that doesn't mean that humanity should pick one or the other as the optimal solution.