Authors examined internal and external determinants of state's adoption of impaired driving laws, using data that included 7 state-level, evidence-based public health laws collected from 1980 to 2010. Event history analyses were used to identify predictors of first-time law adoption and subsequent adoption between state pairs. The independent variables were internal state factors, including the political environment, legislative professionalism, government capacity, state resources, legislative history, and policy-specific risk factors. The external factors were neighboring states' history of law adoption and changes in federal law.

Authors found a strong trend toward an increased number of laws over time. The proportion of younger drivers and the presence of a neighboring state with similar laws were the strongest predictors of first-time law adoption. The predictors of subsequent law adoption included neighbor state adoption and previous legislative action. Alcohol laws were negatively associated with first-time adoption of impaired driving laws, suggesting substitution effects among policy choices.