From the WSJ

In a National Bureau of Economic Research working paper this month, economists at Texas A&M return to Cash for Clunkers, the 2009 stimulus fillip that dispensed vouchers worth as much as $4,500 if people turned in their old cars for destruction and bought a new set of wheels. Mark Hoekstra, Steven Puller and Jeremy West report their "striking" finding that the $3 billion program's two-month run subtracted between $2.6 billion and $4 billion from the auto industry.

The irony is that the goals were to help Detroit through the recession by subsidizing sales and to please the green lobby by putting more fuel-efficient cars on the road. By pulling forward purchases that consumers would make later anyway, the Obama Administration also hoped to add to GDP. Christina Romer, then chair of the Council of Economic Advisers, called Cash for Clunkers "very nearly the best possible countercyclical fiscal policy in an economy suffering from temporarily low aggregate demand."

The A&M economists had the elegant idea of comparing the buying behavior of Texas drivers who owned cars that barely qualified for cash (those that got 18 miles per gallon of gas or less) and those that barely did not (19 mph). Using state DMV sales records, this counterfactual allowed them to isolate the effects of the Cash for Clunkers incentives and show what would have happened without the program.

The two groups were equally likely to purchase a new vehicle over the nine month period that started with Cash for Clunkers, so the subsidy did not create any extra auto business. But in order to meet the fuel efficiency mandate, consumers who got the subsidy were induced to purchase smaller vehicle models with less horsepower that cost on average $2,500 to $3,000 less than those bought by their ineligible peers. The clunkers bought more Corollas, and everybody else more Chevys.

Extrapolated nationally, auto revenues may have plunged by more than what the government spent. And any environmental benefits cannot be justified under the federal social cost of carbon estimate of $33 a ton. Prior research from 2009 and 2013 has shown that the program cost between $237 and $288 a carbon ton.