Okay, well here is where I'm going to attach my comments, since you guys are at least getting close to my angle on these things:
An automated car would indeed be more fuel efficient than a human-driven one, largely because human beings are really stupid at driving: they constantly try to push the car faster than the average speed of traffic, and hence do a lot of standing on the gas and the brake.
(There's another big potential advantage to automated cars, but I bet they're keeping quiet about it in order to keep from scaring people: tailgaiting. If all the cars are computer controlled, they can all brake simultaneously, so there's much less need for big following distances, and hence they can all "draft" each other. Wind resistance is what kills fuel efficiency at highway speeds.)
By fixing a lot of the frustrations with using a private car, these systems are going to encourage using them in preference to other strategies, there's a potential for huge perverse effects: ultimately this isn't a "green" technology, it's a distraction technology that's going to keep people from working on the real problems. (Note: you can say similar things for electric cars-- in the US half our electricity is generated by coal burning, if your electricity is coal-in-disguise it's cleaner to burn gasoline).
Just to pick one problem: if you make it easier for people to live with a 2 or 3 hour commute each way, many more people will do that. Even if you double the energy efficiency, if you double the miles they're willing to drive, that would be a wash.
Another, related angle: one of the big problems the US faces is that after WWII massive amounts of construction was rolled out around the idea that everyone would be driving cars everywhere: the low-density "sprawl" is nearly impossible to retrofit with workable public transit. Does a driverless car sound like a "green-fix" to you? To me it sounds like a "sprawl enabler".
Energy efficiency and environmental pollution isn't everything, there are multiple other problems associated with a car-centered lifestyle from social isolation to gasoline guts. (Oh boy, door-to-door service! I'll never have to walk *anywhere*! I'll never have to sit near anyone with a different ethnic background! Heaven!)
(Brad Templeton's energy numbers on transit are interesting, but limited in a number of ways, largely because he's working solely "per mile": if you take a more whole-system view, a city where people are using relatively dirty buses and trains for short-hops is likely to be better off compared to a sprawl where people are using cleanish-cars to drive 20 miles to buy a gallon of milk.)