Politicians love their Ford Escape hybrids, sure, but does that mean they have to pick a fight with those whose taste in cars runs a bit more toward the old-school? That’s been the question buzzing around various classic-car blogs ever since Diane Feinstein, Susan Collins, and Chuck Schumer introduced a bill to establish a federal “cash for clunkers” program, in which the government would offer to buy up older fuel-inefficient cars and melt them down for scrap. The program would give anyone willing to trade in a car or truck that gets less than 18 miles per gallon a credit of up to $4,500 for buying a new or used car with fuel efficiency at least 25 percent better than the CAFE benchmark for that vehicle class. For those looking to stop driving entirely, the credit could be used for public transportation fares. It’s an idea that has classic -car enthusiasts worried, since some of the cars getting junked would be cars they’d enjoy fixing up, or at least cars they could use for parts.

But there are reasons beyond classic-car nostalgia to be skeptical about a federal trade-in program. The first, noted a while back in a Freakonomics post, is that it’s hard to know how much the "clunker" was actually being driven before it got traded in. Having someone trade in a second or third car that got driven only occasionally does very little to decrease emissions, even if that car was horrendously inefficient. In an attempt to keep people from bringing in cars that were previously sitting on blocks in the yard, the bill stipulates that a car must be drivable and have been registered for the past 120 days to be eligible for the trade-in credit. But with several thousand dollars up for grabs, it might be worthwhile to register an unused car just to qualify for the trade-in.

It’d be easier to forgive this possible lack of cost-effectiveness if not for the fact that it also takes a lot of energy to make a new car. According to a literature review by the Pacific Institute, somewhere between 10 and 20 percent of the life-cycle carbon emissions of the average car come not from driving but from manufacturing and disposal. If a “cash for clunkers” program helped speed the replacement of America’s car fleet—and thereby the rate at which new cars had to be produced—the reduction in tailpipe emissions would be at least partially offset by an increase in manufacturing emissions.

Once again, the final cost-benefit analysis hinges on just how much those clunkers were actually being driven before they got traded in. But it’d be difficult to verify the annual mileage of any given clunker, and, even if it were possible, a program that based trade-in eligibility on having some minimum annual mileage might create a perverse incentive to drive more. Gas-guzzler retirement could turn out to be a real headache, which just goes to show how important it is to have strong fuel-economy standards that keep those inefficient cars off the road in the first place.

--Rob Inglis