[netfire]

I think you are generally right about a primary/family car, but less so for a second, commuter car. I think this mainly hinges around making the self-driving technology safe, reliable and cheap (that is, cheaper than owning a car currently). I think taxis would be used more if they were significantly cheaper. Buses and trains have extra delays for stops, and you may still have to walk/bike after you get off. Having a cheap transportation option once you get off the train would probably increase train ridership as well, and decrease congestion during peak hours (at least for the major freeways, it may increase it some on roads closer to the train station)

[willyt]

Trains should be faster than cars in dense urban environments (if you are close to the station), e.g. London Euston to Watford 19miles 15-20mins by train 32mins by car (outside rush hour).

[cjrp]

Although you do have to enter the station ~5 mins before the train leaves (allowing time to get through the ticket barrier, walk to the platform, board the train), plus exiting at the other end. My train gets into London Bridge in the morning at :32 but I don't get to the street until :36 because of the sheer volume of people. It seems minor, but it does all add up. That said, in rush hour there's no contest - that same journey would take 1 hour+.