As policymakers debate legalizing recreational cannabis use in several US states, the pros of legalization must be evaluated against the cons, including an increase in traffic-related injuries. In a study of traffic fatalities conducted in 2 states that have implemented recreational cannabis laws (RCLs), researchers found that Colorado experienced an increase in traffic fatalities while Washington did not, according to a study published in JAMA Internal Medicine.1
The study authors examined data from 2005 to 2017 in the Fatality Analysis Reporting System, a census of traffic fatality information from the National Highway Traffic Safety Administration, to compare traffic incidents in Colorado and Washington to other states. The primary outcome of the study was the rate of traffic fatalities pre-RCLs and post-RCLs.
Colorado legalized commercial retail sale of cannabis on January 1, 2014; Washington implemented RCLs on December 3, 2013, but researchers chose January 1, 2014 as the first day of exposure for both states. The control group consisted of the 42 states that did not have RCLs. Alaska, Massachusetts, Maine, Nevada, and Oregon were excluded from the donor pool because they implemented RCLs during the study period, and Hawaii was excluded because it is a noncontiguous state.
Compared with its synthetic control (weighted combination of states that best represents fatality rates of the exposed state) in the post-RCL period, there was an estimated equivalent of 75 excess fatalities in Colorado per year (1.46 deaths per 1 billion vehicle miles traveled [VMT]). When neighboring states were excluded, the difference between Colorado and pre-RCL Colorado was 1.84 fatalities per 1 billion VMT per year (94 excess deaths per year); when states that implemented medical cannabis laws (MCLs) were excluded, there were 2.16 fatalities per 1 billion VMT per year (111 excess deaths per year).