How CAFE standards hurt the environment

I never understood the argument for CAFÉ (Corporate Average Fuel Economy), the law that forces auto manufacturers to increase the miles per gallon fuel efficiency of their cars. How could it possibly be a good thing to force -- by a top-down Soviet-style mandate -- which cars can and cannot be produced?  People make a zillion tradeoffs when deciding which car to buy -- safety, size, convenience, prestige, economy -- so why not let the manufacturers make the same set of tradeoffs?  Interfering in that process is a sure way to invite unintended consequences.

Don't get me wrong: I obviously think that saving gas is a good thing (heck, I drive a Prius!) But if we think gasoline consumption is too high, there are far better ways to discourage consumption, such as raising the tax on gas, or for that matter, the tax on gas guzzling vehicles.  Or, as the Seattle Times writes today, put tolls on our roads and bridges.

But here's the best reason of all for dumping the CAFÉ: it hurts the environment.  A study by Andrew Kleit, from Pennsylvania State University shows why:

Because the pollution from a car is a direct function of the number of miles it is driven, and people in more fuel-efficient vehicles drive more, the net result from an increase in cafe standards is an increase in automobile pollutants.

If you think about it, this is just common sense.   All other things being equal, you will drive more if your car costs less to drive.  I find this happening all the time myself: because my car gets 44+mpg, I don't think twice about taking trips that I might avoid if I were worried about gas prices.

How much worse will the air get under the new CAFE laws proposed by Obama and others?

	% increase because of CAFE
VOC Emissions	2.30%
NOx Emissions	4.97%

These are increased pollutants that Kleit computes will result from the extra driving that is an inevitable consequence of raising CAFE standards to 35mpg or more.  The math behind this isn't terribly complicated: just ask how much more people will drive thanks to better fuel efficiency and multiply by the additional pollutants expelled per mile.

Now of course you can immediately suggest that we double-down on the regulations and force both higher CAFE numbers and lower emissions. But what will be the unintended consequences of that?