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).
When Colorado and Washington were pooled together, researchers identified 0.87 deaths per 1 billion VMT per year. Implementation of RCLs was not associated with an increase in traffic fatalities in Washington alone; 28 of 42 control states had a post-RCL: pre-RCL ratio higher than or equal to that of Washington.
The study authors hypothesize that Colorado’s increase in traffic fatalities may be due to its cannabis tourism industry, and lack of neighboring states that implemented RCLs during the study period compared with Washington.
“A higher number of neighboring states without RCLs can lead to a higher volume of out-of-state drivers buying, using, and driving under the influence of cannabis. Colorado has no neighboring states with RCLs, whereas in contrast, Washington State shares borders with Oregon, which implemented RCLs in 2015, and with Canada, which implemented MCLs in 2001,” researchers stated.
In an accompanying editorial, clinicians discuss the inconsistency of observed effects of RCLs on traffic fatality rates.2 The editorial authors called for additional research on how cannabis legalization affects impaired driving and traffic fatalities.
“Strong data will be required to build an evidence-based foundation that will inform testing, enforcement, and policy related to cannabis use and impaired driving with the ultimate objective of reducing, and even eliminating, road fatalities,” the editorial authors write.
- Santella-Tenorio J, Wheeler-Martin K, DiMaggio CJ, et al. Association of recreational cannabis laws in Colorado and Washington state with changes in traffic fatalities, 2005 to 2017. JAMA Intern Med. 2020;180(8):1061-1068.
- Rosekind MR, Ehsani JP, Michael JP. Reducing impaired driving fatalities data need to drive testing, enforcement, and policy. JAMA Intern Med. 2020;180(8):1068-1069.