That's a completely useless comparison that applies almost no where in the world? You need to compare driving vs pervasive transit and bike networks. I doubt New Yorkers or Amsterdammers would accept your efficient car hypothesis.

In the few places with high 100% walking commutes, I don't see cars being more efficient either. Do you want every college student to drive from their dorm to class? How about poor countries without the money to maintain good road networks?