How about a good cruise driver? For example, when i reach a hill, I hit cancel so the car slows down. When I reach the top I hit set. Then on the decline, I tap the accel button so it gradually goes back to its speed. With a tailwind I average 60mpg doing around 60 on the freeway (which is about average during rush hour)
On the way home, though, going east into the wind, the average is much lower - 52 mpg.