The problem with transit systems is that they aren't designed for competition. They're costly to make, have few builder companies to choose from (who all know the game very well and go over budget as a tactic), and extremely difficult to overhaul/retrofit when more efficient tech becomes available.

They're great for short distance travel in densely populated areas, but outside of that I doubt they'd hold up in long-term cost and efficiency vs autonomous electric cars for long.

As for parking, a fully autonomous car service would allow a car to come to you and pick you up. So it wouldn't need to park near where you are.