In the movie "The 6th Day" (silly Schwarzenegger sci-fi flick, but bear with me) there's a scene where they're driving to work, and they switch to automated guidance just for the highway portion of the trip. The car warns them when they're approaching their exit and that they must resume manual control of the vehicle, and it will shut down unless they confirm.
I thought that that was an interesting and plausible early step towards fully automated vehicles. The interstates and other highways will be the first to have the necessary guidance systems to interface with your vehicle; it'll be a while before all side streets and other surface roads will be fully compliant. Of course we know now that it will probably be done via GPS, but even so, Google maps aren't always 100% up-to-date, and are never 100% accurate anyway. Anyone who's taken enough road trips following their directions knows that.