At least in urban areas, you're eventually going to end up having vehicle performance arbitrated via radio by a computer network outside the vehicles. (I'm pretty sure it's much easier than trying to do everything "peer to peer," if you will) This gets you intersections where nobody has to fully stop and vehicles merely coordinate and modulate their speed, which is a pretty powerful efficiency advantage in itself.

With a system like that you could easily design a market where vehicles can choose to pay a toll to get a favorable path through traffic. You might see a few options and incentives given for choosing a more fuel-efficient path, etc.