Autonomous vehicles on designated lanes will be everything from Y class buses (hoping that they consider Y+) to private cars with facilities. Speed will be fast, but it does not have to be as fast as a plane or highspeed rail IF it can be productive time, whether business, studying, or sleeping. The capacity of a single exclusive lane will far exceed the current capacity. Optimal distance for surface to air travel will change. We have discussions now over drive versus fly for 250 mile trips. It will be considerably higher. Door to door via autonomous vehicle(s) may challenge both rail and flying even for that 400 miles between LA and SF.
I think people have their hopes up way too high on autonomous technology being applied to cars, trucks, and busses. We have a ways to go before it becomes proven technology in real world environments, and even then there will be a much longer way to go before it becomes commonplace. Even when it's commonplace there will still be people who insist on doing the driving (like how some people still choose a manual transmission over automatic) and so the benefits of autonomous vehicles won't be fully realized.
Also you can already be productive on a bus, train, and plane. All of those modes of transportation are proven technology that we can implement now, but for some reason people have really jumped on the hype of autonomous cars and some seem to think it'll be a cure-all for our transportation issues.
Too many airports to fit in signature.