I think self driving tech will allow a new category of mass transportation. Not a taxi, not a bus, but something like uberpool. You walk one or two blocks to a major street, get picked up by a vehicle that holds ~12 people max. The vehicles route and passenger selection is optimized to reduced starts and stops. Complicated routes may need transfers, but for most travelers, they'll have less walking between pickups/dropoffs and destinations than current mass transit options, faster travel times, and they won't contribute to congestion at the scale that individual taxis would.