By Mark Hoekstra, Steven L. Puller, and Jeremy West, American Economic Review, July 2017. Abstract:
The 2009 Cash for Clunkers program aimed to stimulate consumer spending in the new automobile industry, which experienced disproportionate reductions in demand and employment during the Great Recession. Exploiting program eligibility criteria in a regression discontinuity design, we show more than half of the subsidies went to households who would have purchased during the two-month program anyway; the rest accelerated sales by no more than eight months. Moreover, the program’s fuel efficiency restrictions shifted purchases toward vehicles that cost on average $7,600 less. Thus, we estimate on net the $3 billion program reduced total new vehicle spending by $5 billion.
A summary is freely available here.