I think that goes to the parent's point: making the individual cars more efficient is not going to make a difference in the big picture. For one, the increase in efficiency has really already been met by an increase in power and performance - even the humble Prius has made an effort at faster 0-60, not to mention the sub-3-second super-SUVs.

But if driving a car is cheaper (and more fun) then we are doomed to dedicate more land to asphalt, and all the hidden costs thereof.