Emily Badger:

Driving has been on the decline in the United States since 2004, as researchers have documented every which way. What they still don’t know, though, is precisely why. The answer likely has to do with some messy mix of rising gas prices, changing demographics, new technology, a souring economy and the shifting preferences of Millennial drivers. But it’s tempting to lean on some of those explanations more heavily than others.

The economic theory is a particularly deceptive one. If you believe that driving trends have gone south because the economy has, too, then that means U.S. policy doesn’t need to adjust to a new transportation reality less focused on cars. Wait long enough, and everything will go back to the old normal.

Years will have to pass before we can look back on this moment and know for sure if the decline in driving was primarily a product of the economy or something else. For now, though, the U.S. PIRG Education Fund has proposed a “natural experiment” with the data we do have: vehicle mileage per capita by state. If the economy is a major factor here, then states hardest hit by the recession – with the steepest rise in unemployment – would experience the most significant drop in driving, right? For one thing, unemployed people without jobs to drive to don’t drive as much.

Via Steven Sinofsky