The vast majority of drivers everywhere in the world do not try to maximize their mileage. Their choice of vehicle, how and when they drive, why they get in a vehicle, none of that is designed around using the least amount of gas. Usually the highest priority is to use the least amount of time.
So do not let humans drive. Build a System that drives for you. Tell it where you need to go, it will get you there.
Give the system enough control, and it will coordinate traffic to preempt traffic backups, prevent accidents and gapers blocks, automatically route around road repairs, dignitary caravans, police action, stray animals on the road, you name it.
Most importantly, automated cars will be moved with an eye toward mileage. Sure, velocity and acceleration are more mellow, but since traffic is carefully routed around itself, vehicles still wind up getting somewhere faster. When all the vehicles on these particular roads are automated, stoplights and stop signs are discarded. Vehicles move slower and safer; if you want to cross a road, just go ahead and cross, the system will see a pedestrian step off the curb and have vehicles defer to you. Vehicles crossing an intersection will automatically interleave, but stop for pedestrians.
And, best of all, the system will always, always, always see bicyclists. Doors will refuse to open when a bicyclist wheels by.