No mention of the energy cost of Aluminum, unless you recycle, like beercans maybe?
Why Cars Don't Get 50mpg | Newsweek Voices - Keith Naughton | Newsweek.com:
"Consider the exercise Ford just went through. It ran a computer simulation on what would happen to the mileage of a Ford Focus small car if you built it entirely out of lightweight aluminum. Losing the steel allowed the Focus to drop 1,000 pounds—30 percent of its body weight. That enabled Ford to outfit it with a tiny one-liter engine, half the size of its old engine, but far more fuel efficient because of new technology. Best of all, the small motor goes just as fast as the big one because the car is so much lighter. The result: fuel economy on this fabulous Focus went from 35mpg to 50mpg. What's stopping Ford from moving this car from pixels to pavement? The cost of an all-aluminum car could top $50,000—not a sum the typical economy-car buyer is willing to pay. 'What's going to be the cost acceptance for this much improvement in fuel economy?' asks Dan Kapp, director of Ford's advanced engines and transmissions. 'We don't know yet.'"
More on weight here : The evidence of weight - AutoWeek Magazine
Creature comforts and safety mandates add pounds.