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Original Investigation
Health Care Policy and Law
June 22, 2020

Association of Recreational Cannabis Laws in Colorado and Washington State With Changes in Traffic Fatalities, 2005-2017

Author Affiliations
  • 1Center for Opioid Epidemiology and Policy,Division of Epidemiology, Department of Population Health, New York University School of Medicine, New York, New York
  • 2School of Basic Sciences, Universidad del Valle, Cali, Colombia
  • 3Department of Surgery, New York University School of Medicine, New York, New York
  • 4Society and Health Research Center and School of Public Health, Universidad Mayor, Santiago, Chile
  • 5Department of Epidemiology, Columbia University Mailman School of Public Health, New York, New York
  • 6Division of Translational Epidemiology, Vagelos College of Physicians and Surgeons, Columbia University, New York, New York
  • 7Division of Translational Epidemiology, New York State Psychiatric Institute, New York, New York
JAMA Intern Med. 2020;180(8):1061-1068. doi:10.1001/jamainternmed.2020.1757
Key Points

Question  Have traffic fatalities increased after the implementation of recreational cannabis laws in Colorado and Washington State?

Findings  Using a synthetic control approach, this ecological study found that recreational cannabis laws were associated with increases in traffic fatalities in Colorado (mean of 75 excess fatalities per year) but not in Washington State.

Meaning  These findings suggest that unintended effects of recreational cannabis laws can be heterogeneous and may be specific to variations in how these laws are implemented (eg, density of recreational cannabis stores).

Abstract

Importance  An important consequence of cannabis legalization is the potential increase in the number of cannabis-impaired drivers on roads, which may result in higher rates of traffic-related injuries and fatalities. To date, limited information about the effects of recreational cannabis laws (RCLs) on traffic fatalities is available.

Objective  To estimate the extent to which the implementation of RCLs is associated with traffic fatalities in Colorado and Washington State.

Design, Setting, and Participants  This ecological study used a synthetic control approach to examine the association between RCLs and changes in traffic fatalities in Colorado and Washington State in the post-RCL period (2014-2017). Traffic fatalities data were obtained from the Fatality Analysis Reporting System from January 1, 2005, to December 31, 2017. Data from Colorado and Washington State were compared with synthetic controls. Data were analyzed from January 1, 2005, to December 31, 2017.

Main Outcome(s) and Measures  The primary outcome was the rate of traffic fatalities. Sensitivity analyses were performed (1) excluding neighboring states, (2) excluding states without medical cannabis laws (MCLs), and (3) using the enactment date of RCLs to define pre-RCL and post-RCL periods instead of the effective date.

Results  Implementation of RCLs was associated with increases in traffic fatalities in Colorado but not in Washington State. The difference between Colorado and its synthetic control in the post-RCL period was 1.46 deaths per 1 billion vehicle miles traveled (VMT) per year (an estimated equivalent of 75 excess fatalities per year; probability = 0.047). The difference between Washington State and its synthetic control was 0.08 deaths per 1 billion VMT per year (probability = 0.674). Results were robust in most sensitivity analyses. The difference between Colorado and synthetic Colorado was 1.84 fatalities per 1 billion VMT per year (94 excess deaths per year; probability = 0.055) after excluding neighboring states and 2.16 fatalities per 1 billion VMT per year (111 excess deaths per year; probability = 0.063) after excluding states without MCLs. The effect was smaller when using the enactment date (24 excess deaths per year; probability = 0.116).

Conclusions and Relevance  This study found evidence of an increase in traffic fatalities after the implementation of RCLs in Colorado but not in Washington State. Differences in how RCLs were implemented (eg, density of recreational cannabis stores), out-of-state cannabis tourism, and local factors may explain the different results. These findings highlight the importance of RCLs as a factor that may increase traffic fatalities and call for the identification of policies and enforcement strategies that can help prevent unintended consequences of cannabis legalization.

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    2 Comments for this article
    Colorado cannabis fatalities
    Karl Stecher, M.D. | retired neurosurgeon
    When the recreational law passed (actually, when the medicinal law passed, as many obtained prescriptions), there was a huge influx of out of staters to Colorado to participate in the industry and the fruits thereof. One might investigate how many of the deaths occurrred in people who had lived in Colorado ten years of more vs the newcomers.
    CONFLICT OF INTEREST: None Reported
    Insufficient data discrimination
    Richard Vance, MBA, BSEE | Retired Complex Systems Engineer
    There is no there here.
    CONFLICT OF INTEREST: None Reported
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