Electric cars seem to be a pretty good solution, though the cars of the future will probably be much smaller - right now we pad them a lot with extra metal and plastic so that the passengers can survive a collision. With self-driving cars you won't need that anymore. I imagine the future of cars is a PRT[0] system - it's a perfect thing for a city. As for travel between cities, that's what trains are for.
In terms of efficiency, is using the same technology (cars) in a different way - removing the driver - really going to have long term affects?
My guess is that cars themselves will be out of production before we reach 100% adoption of driverless cars.