In the Weeds of Traffic Fatalities: Replication Dataset

This replication package accompanies the article “In the Weeds of Traffic Fatalities: Revisiting the Effect of Medical Marijuana Laws.” The research re-evaluates the widely cited finding that medical marijuana laws (MMLs) significantly reduce traffic fatalities. The central hypothesis is that previous estimates of MML effects may be biased due to unaccounted-for pre-treatment trends and hard to interpret because of heterogeneity across states.

The dataset is a panel of U.S. states from 1990 to 2010, constructed to closely replicate Anderson et al. (2013). It includes annual, state-level traffic fatality rates (log-transformed per 100,000 population), a binary indicator for MML adoption, and a rich set of covariates covering demographics, driving laws, traffic enforcement measures, and substance-related policies.

The key finding is that states legalizing medical marijuana were already experiencing declining traffic fatalities before legalization. When accounting for these pre-trends using the Imputation Procedure (Borusyak et al., 2024), the estimated effect of MMLs shifts from negative to either zero or positive—depending on included covariates. The data also reveal large heterogeneity across states, with California disproportionately influencing population-weighted estimates.