The answer to better mpg, traffic shaping, less accidents is - as much as I hate to say it - is autonomous cars.
They can drive at the best measured MPG zone, they don't get distracted, they have faster response times than human drivers. They don't hit the gas pedal stopping you from merging onto the highway or changing lanes, they don't pass illegally or drive recklessly. Numerous studies have shown that traffic jams are simply caused by people following too closely.
I don't know for sure, but I really think the next evolution of vehicle transport will be autonomous.