Are more laws better? The case of traffic fatalities in the US, 1982-2008

Objective: Fatalities from motor vehicle crashes remain a leading cause of death and vary up to 5-fold among different states. This study examines state adoption of 25 evidence-based public policies focused on protecting occupant and driver safety, reducing underage and excessive drinking, penalizing drunk driving, and reducing other unsafe driving practices from 1982-1998 and quantifies the combined impact of these policies on traffic fatalities. Methods: Ecological time series/cross-sectional design, employing fixed effects negative binomial regression models of state-level traffic fatalities per 100 million vehicle miles traveled. State policy comprehensiveness is measured by the proportion of the 25 evidence-based policies states have adopted at each year. Models control for state-level demographics, resources, and additional risk factors. Results: States vary substantially in the extent to which they have adopted a comprehensive package of the 25 policies examined here. A more comprehensive policy environment is negatively associated with motor vehicle fatalities, once other factors are controlled: a 1 unit increase in our policy measure is associated with a 1% decrease in traffic fatalities. If states with the lowest policy adoption levels were to adopt the laws present in states with the highest levels, they could potentially reduce traffic fatalities by as much as 20 percent, all else being equal. Conclusion: This study is unique in assessing the combined impact of a large number of policies simultaneously. It shows that the policy environment is an important contributor to traffic fatalities, and suggests the need for increased adoption of evidence-based policies to reduce traffic fatalities.