The case of the missing gas mileage
Contrary to common perception, the major automakers have produced large increases in fuel efficiency through better technology in recent decades. There’s just one catch: All those advances have barely increased the mileage per gallon that autos actually achieve on the road.Sound perplexing? This situation is the result of a trend newly quantified by MIT economist Christopher Knittel: Because automobiles are bigger and more powerful than they were three decades ago, major innovations in fuel efficiency have only produced minor gains in gas mileage. Specifically, between 1980 and 2006, the average gas mileage of vehicles sold in the United States increased by slightly more than 15 percent — a relatively modest improvement. But during that time, Knittel has found, the average curb weight of those vehicles increased 26 percent, while their horsepower rose 107 percent. All factors being equal, fuel economy actually increased by 60 percent between 1980 and 2006, as...