1198 [Journal of Political Economy, 2001, vol. 109, no. 6]  2001 by The University of Chicago. All rights reserved. 0022-3808/2001/10906-0005$02.50 How Dangerous Are Drinking Drivers? Steven D. Levitt University of Chicago and American Bar Foundation Jack Porter Harvard University We present a methodology for measuring the risks posed by drinking drivers that relies solely on readily available data on fatal crashes. The key to our identification strategy is a hidden richness inherent in two- car crashes. Drivers with alcohol in their blood are seven times more likely to cause a fatal crash; legally drunk drivers pose a risk 13 times greater than sober drivers. The externality per mile driven by a drunk driver is at least 30 cents. At current enforcement rates the punishment per arrest for drunk driving that internalizes this externality would be equivalent to a fine of $8,000. I. Introduction Motor vehicle crashes claim over 40,000 lives a year in the United States, approximately the same number of Americans killed over the course of either the Korean or Vietnam wars. The death toll in motor vehicle accidents roughly equals the combined number of suicides and homi- cides, and motor vehicle deaths are 30 times as frequent as accidental deaths due to firearms. Motor vehicle accidents are the leading cause of death for Americans aged 6–27. We would like to thank Joe Altonji, Gary Chamberlain, Austan Goolsbee, Lars Hansen, James Heckman, Guido Imbens, James Poterba, Kenneth Wolpin, two anonymous referees, the editor Robert Topel, and numerous seminar participants for helpful comments and advice, as well as Christopher Ruhm for generously providing us with data. Financial support of the National Science Foundation is gratefully acknowledged.