> Why would self-driving cars be better than mass-transit?
They are better for some things and worse for others. They are less efficient per passenger-mile, so they are worse for high-traffic arteries. OTOH, they are cheaper per mile travelled, so they are better for connecting the endpoints to the well-travelled arteries, and in some cases (where relatively little of the trip is on a well-travelled artery where mass transit is efficient) for end-to-end services.
They are better for some things and worse for others. They are less efficient per passenger-mile, so they are worse for high-traffic arteries. OTOH, they are cheaper per mile travelled, so they are better for connecting the endpoints to the well-travelled arteries, and in some cases (where relatively little of the trip is on a well-travelled artery where mass transit is efficient) for end-to-end services.