New Evidence on the Causal Impact of Traffic Safety Laws on Drunk Driving Fatalities

In the United States, about 28 lives are lost daily in motor vehicle accidents that involve an alcohol-impaired driver. While most states have enacted traffic-safety laws to address this phenomenon, little consensus exists on the causal impact of these laws in reducing drunk-driving fatalities. This paper exploits quasi-random variation in state-level laws to estimate the causal effect of select traffic laws on the frequency of fatal accidents involving a drunk driver. This is identified from the discontinuities in policy treatments among homogeneous contiguous-counties that are separated by a shared state border. This approach addresses the econometric issues created due to spatial heterogeneity that may have biased previous studies. We present convincing evidence that the estimates in the literature are prone to an upward bias. Further, if the effective laws were adopted as a federal mandate in 1986, they could have prevented about 24% of drunk-driving motor-vehicle fatalities.