This originally appeared at https://rrs.scholasticahq.com/article/30970-state-marijuana-laws-and-traffic-fatalities
We examine the relationship between traffic fatalities and state marijuana laws using data from 1985 through 2019 and Poisson difference in difference models that allow effects to vary over time. We show numerous attributes of state marijuana laws are captured by a single underlying dimension, implying interdependence and potential inseparability of the effects of recreational marijuana laws (RMLs) and prior medical marijuana laws (MMLs). Controlling for MMLs, we find no statistically significant change in fatalities associated with RMLs, while, as in earlier work, MMLs are associated with lower fatalities. There is a statistically insignificant decline in fatalities in states bordering RML states. Type 1 error rate inflation is present in this context, but it is not strong enough to overturn the finding that lower fatalities followed MMLs.