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 o
ur 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 sobe
r 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 dr
iving that internalizes this externality would be equivalent to a fine of $
8,000.