Raising fuel economy standards makes for a pretty photo op

But alas, no free lunch:

• It will raise the prices of cars, and make them less safe
• It will reduce our carbon emissions, but not by as much as advertised, because more fuel efficient cars make driving cheaper, so people will do more of it. This "rebound" effect robs about 25% of gains, and also means more congestion, and more wear-and-tear on roads
• If you want to cut down on the pollution from driving, this is about the worst possible way to do it.