I see a very long period where a trip will involve both manual and automated driving.
Initially I'll manually go out the driveway and through the neighborhood (where there is no stripe to stay between) and collector streets (where some kid painted over a stop sign hiding it from sensors). Only when I get on the interstate will I put it on autopilot. I'll have to take it off to exit.
There will be a government sponsored GIS database, continuously and automatically updated, that will determine "autopilot safe" roads that have all the necessary features for your sensors to work. The car GPS will link to this database to enable/disable autopilot depending on what road you're on, but you'll still choose if you want to use it. Something like a construction zone or a wreck would change an autopilot road to manual only. I think drivers and driverless sharing the road will be no more dangerous than the current setup.
Then, as we get comfortable with the technology, mandatory autopilot roads will start to pop up beginning with major highways. Your car will go auto as soon as you're on the road and you cant change it. Only then will we be able to utilize the higher speeds and drafting. Over time nearly all roads will become mandatory auto as local governments implement the necessary features on the smaller roads.