Investigation of associations between marijuana law changes and marijuana-involved fatal traffic crashes: A state-level analysis

In this study, associations of five types of marijuana law changes and marijuana-involved fatal crashes (i.e., a fatal crash involving a driver who tested positive for marijuana) in the United States are analyzed: (1) prohibition to medical legalization; (2) prohibition to decriminalization; (3) decriminalization to the combination of medical legalization and decriminalization; (4) medical legalization to full legalization; and (5) the combination of decriminalization and medical legalization to full legalization. The fatal crash data were collected from the Fatality Analysis Reporting System (FARS) database, archived by the National Highway Traffic Safety Administration (NHTSA). Using these five types of changes, the results showed that (1) Arizona and New Jersey experienced no significant changes. (2) Massachusetts experienced 174.5% relative increases after decriminalization. (3) The relative number increased by 75.3% in Connecticut after medical legalization when decriminalization was already in place. (4) A 31.2% relative increase in Washington was observed. (5) The relative number increased by 63.1% in Colorado. In conclusion, no significant changes in the number of marijuana-related crashes were observed after medical legalization only. Nevertheless, an increased number of marijuana-related crashes were observed after all other types of the marijuana law changes.