As the movement to decriminalize marijuana has gained more support throughout the United States, as of early 2017, 21 states have decriminalized the possession of a small amount of marijuana for personal recreational use, and more states are expected to decriminalize marijuana (GOVERNING 2017). Despite this strong move toward decriminalizing marijuana, however, the consequences of implementing such a policy are still very much unknown. One of the concerns regarding this movement to decriminalize marijuana is its potential impact on road safety (Schrader 2015; Roberts 2017; Halsey 2015). Although there are a few studies that have examined the association between marijuana use and availability and traffic fatalities, these studies are correlational in nature and show divergent outcomes (Anderson and Ree 2011; Anderson et al. 2013). Furthermore, these studies do not examine the impact of decriminalizing marijuana on road safety. In order to fill this gap, my research investigates the causal association between marijuana decriminalization and traffic fatalities by using the synthetic control method, pioneered by Abadie et al. (2010). This study estimates the causal effects of 2009 Massachusetts's marijuana decriminalization on Massachusetts' total traffic fatalities by comparing Massachusetts's trends in total traffic fatalities and its synthetic counterpart. The results of this study show a temporary increase in the number of total traffic fatalities in Massachusetts compared to its synthetic counterpart between 2009 and 2012, suggesting marijuana decriminalization's detrimental effect on road safety. Future studies should consider investigating the heterogeneous effects of marijuana decriminalization on traffic fatalities based on age groups, gender, and residential density and the causal mechanism between marijuana decriminalization and traffic fatalities.



College and Department

Family, Home, and Social Sciences; Sociology



Date Submitted


Document Type





marijuana, marijuana decriminalization, traffic fatalities, road safety, policy



Included in

Sociology Commons