I think it's cool to see how much gas will be saved with these autonomous cars, seeing as people tend to drive in a manner that is not conducive to efficient fuel usage (i.e. late braking for a red light, etc.). But then again, from videos I've seen, they seem to accelerate very slowly and brake too much for turns, which is also not efficient.
Being able to slow down so the car can approach a red light as it turns green should save a bunch of gas. Heck. Just driving the speed limit alone will save fuel. Both techniques will drive the majority of today's drivers nuts.
All the autonomous cars will be electric anyway, so as for saving gas, well.
I just read they standardised wireless EV charging points now too, coming later this year, so EV's will be able to just drive over a pad in the road to self charge, not needing a human to plug them in at all.