[mirrorlake]

The best MPG you can get on the highway is just the slowest you can safely go without confusing other drivers, making people angry, or getting pulled over by the police. Drag is proportional to velocity squared, so every increase in mi/hr wastes more energy pushing air out of the way of the car.

To answer your regenerative braking question: braking is inefficient by default, so just avoid tapping the brakes in situations where you could coast.

With regenerative braking, you'll never get back 100% the energy because of thermodynamics. There's always wasted energy any time energy is moved, transformed, stored, etc.

[tzs]

Go too slow though and mileage goes down. At 60 mph my car gets around 25 mpg. At 1 mph it would get around 3 mpg.

That's because my car never consumes less than around 0.3-0.4 gallons per hour when the engine is running.