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The authors

University of Northern British Columbia, Northern Medical Program, 3333 University Way, Prince George, British Columbia, V2N 4Z9, Canada

Centre for Addiction and Mental Health (CAMH), Human Brain Laboratory, 250 College Street, Toronto, Ontario, M5T 1L8, Canada

cUniversity of Victoria, Canadian Institute for Substance Use Research (CISUR), 2300 McKenzie Avenue, Victoria, British Columbia, V8N 5M8, Canada

dCentre for Addiction and Mental Health (CAMH), Krembil Centre for Neuroinformatics, 250 College Street, Toronto, Ontario, M5T 1L8, Canada

eUniversity of British Columbia, Faculty of Medicine, MD Undergraduate Program, 317-2194 Health Sciences Mall, Vancouver, British Columbia, V6T 1Z3, Canada

fDepartment of Community Health and Epidemiology, Department of Emergency Medicine Centre for Clinical Research, Room 407, 5790 University Ave, Halifax, Nova Scotia, B3H 1V7, Canada



Worldwide momentum toward legalization of recreational cannabis use has raised a common concern that such policies might increase cannabis-impaired driving and consequent traffic-related harms, especially among youth. The current study evaluated this issue in Canada.


Utilizing provincial emergency department (ED) records (April 1, 2015-December 31, 2019) from Alberta and Ontario, Canada, we employed Seasonal Autoregressive Integrated Moving Average (SARIMA) models to assess associations between Canada’s cannabis legalization (via the Cannabis Act implemented on October 17, 2018) and weekly provincial counts of ICD-10-CA-defined traffic-injury ED presentations. For each province (Alberta/Ontario), SARIMA models were developed on two driver groups: all drivers, and youth drivers (aged 14–17 years in Alberta; 16–18 years, Ontario).


There was no evidence of significant changes associated with cannabis legalization on post-legalization weekly counts of drivers’ traffic-injury ED visits in: (1) Alberta, all drivers (n = 52,752 traffic-injury presentations), an increase of 9.17 visits (95 % CI -18.85; 37.20; p = 0.52); (2) Alberta, youth drivers (n = 3265 presentations), a decrease of 0.66 visits (95 % CI -2.26; 0.94; p = 0.42); (3) Ontario, all drivers (n = 186,921 presentations), an increase of 28.93 visits (95 % CI -26.32; 84.19; p = 0.30); and (4) Ontario, youth drivers (n = 4565), an increase of 0.09 visits (95 % CI -6.25; 6.42; p = 0.98).


Implementation of the Cannabis Act was not associated with evidence of significant post-legalization changes in traffic-injury ED visits in Ontario or Alberta among all drivers or youth drivers, in particular.


Implementation of cannabis legalization frameworks has raised a common concern that such legislation might increase population-based traffic-related morbidity and mortality (Hall and Lynskey, 2020; Leyton, 2019), especially among youth (Canadian Association of Chiefs of Police, 2017; Grant and Bélanger, 2017). Some have predicted that legalization of recreational cannabis use would decrease cannabis prices and perceived harmfulness, increase cannabis availability, eliminate criminal penalties as a deterrent to use, and make cannabis use more socially acceptable – all factors which would likely contribute to population-level increases in cannabis use, cannabis-impaired driving, and cannabis-related traffic harms (Hall and Lynskey, 2016; Pacula and Smart, 2017). Given research suggesting that cannabis use and its associated impairments appear to confer relatively greater crash risk for young inexperienced drivers in comparison to older, more seasoned drivers (Brubacher et al., 2020), a reasonable argument can be made that cannabis legalization might increase traffic-related harms among young people, especially as cannabis-impaired driving is more prevalent among adolescents in some jurisdictions (e.g., Canada) than alcohol-impaired driving (Boak et al., 2020).

The Canadian Federal government implemented the legislative framework (the Cannabis Act) for national cannabis legalization on October 17, 2018 (Parliament of Canada, 2018). A central, explicit goal of the Cannabis Act aims to prevent cannabis use and related harms among youth (Parliament of Canada, 2018), with the Health Canada Task Force on Cannabis Legalization and Regulation asserting, “Youth are at the centre of the Government’s objectives in pursuing a new system of regulated legal access to cannabis”(Health Canada, 2016)(p13). The Act not only allows adults and youth to possess cannabis for personal consumption or sharing [adults: up to 30 g of dried cannabis (or equivalent); youth: up to 5 g of dried cannabis (or equivalent)], but also establishes a commercial retail cannabis market, legally restricted to those at least the minimum legal cannabis sales age (18 years in Alberta and Québec; 19 years in the rest of the country). In contrast to the Canadian approach, US states legalizing adult recreational cannabis use typically have retained pre-legalization restrictions and penalties regarding youth cannabis possession and other cannabis-related offenses (Plunk et al., 2019).

In the body of literature assessing the possible impacts of cannabis legalization on motor vehicle collision (MVC) outcomes, almost all available studies have based their analyses on data from the same publicly available source – the US Fatal Accident Reporting System (FARS), a national data registry capturing detailed information on all motorist and non-motorist fatalities (regardless of age) related to motor vehicle collisions in the United States. In FARS-based studies utilizing whole-population samples, cannabis legalization occurring in recreational-cannabis-law (RCL) states has been associated with: (1) no evidence of significant post-legalization changes in motor vehicle traffic fatalities (Aydelotte et al., 2017; Hansen et al., 2018); (2) significant increases in post-legalization motor vehicle traffic fatalities (Aydelotte et al., 2019; Kamer et al., 2020); and (3) significant increases in post-legalization motor vehicle traffic fatalities in some RCL states, but not in other RCL states (Lane and Hall, 2019; Santaella-Tenorio et al., 2020). In light of the mixed findings from FARS-based studies, the likely effects of cannabis legalization on US traffic-fatality outcomes remain uncertain.

In addition to the FARS-based studies, only a couple of other projects have evaluated the impacts of cannabis legalization on traffic-related outcomes. The US Highway Data Loss Institute (HDLI) undertook a study assessing the impacts of the opening of state-sanctioned retail cannabis sales in Washington, Colorado, and Oregon, and they found that retail sales availability for cannabis products was significantly associated with increases in collision claim frequencies (Highway Data Loss Institute, 2017). Using data from state-level motor vehicle collision insurance claims from target RCL states and nearby “control” non-RCL states, the HDLI study reported that the date of the opening of cannabis retail outlets was associated with significant increases in collision claim frequencies: 6.2 % in Washington; 13.9 % in Colorado; and 4.5 % in Oregon (Highway Data Loss Institute, 2017). Also, using an interrupted timeseries approach, researchers found that cannabis legalization in Uruguay was associated with significant national increases in motor vehicle fatalities (Nazif‐Munoz et al., 2020).

At this time, the inconsistent scientific evidence does not support a clear position on the potential impacts of cannabis legalization on traffic-related harms, especially as the bulk of cannabis-legalization studies have focused almost exclusively on traffic fatalities (a relatively small subset of the full scope of traffic-related harms) in the United States. More work is required to understand how cannabis legalization might affect a broader range of traffic-related harms, especially in other jurisdictions and in key subpopulations. The current study aims to contribute to the existing literature by: (1) evaluating the associations between Canada’s cannabis legalization and traffic-injury conditions sufficiently severe to warrant emergency department (ED) utilization in Alberta and Ontario; and (2) focusing on youth drivers – a subpopulation of special concern in the Canadian cannabis-legalization framework – as well as all drivers, regardless of age. Given Statistics Canada survey data showing significant post-legalization increases in past-90-day prevalence of cannabis use in the Canadian population (Rotermann, 2020), we tentatively expected that the implementation of Canada’s Cannabis Act would be associated not only with population-based increases in ED presentations for drivers’ injuries due to motor vehicle collisions, but also with increases in MVC-related injury ED visits specifically among youth drivers.

Section snippets


The Centre for Addiction and Mental Health (CAMH) Research Ethics Board (REB) provided ethical approval for the current study (REB# 073/2019). The Canadian Institute for Health Information (CIHI) provided de-identified data for the project, and patient consent was not required for release of these data.

Data source: National Ambulatory Care Reporting System (NACRS), April 1, 2015– December 31, 2019.

The current study utilized provincial Ontario and Alberta ED data spanning from April 1,


The analytic samples consisted of all drivers’ MVC ED visits occurring during the data span (April 1, 2015-December 31, 2019) in Alberta [all drivers’ visits, n = 52,752 (comprised of 45.8 % female visits); youth-driver presentations, n = 3265 (including 54.7 % female visits)] and in Ontario [all drivers’ presentations, n = 186,921 (including 48.6 % female visits); youth drivers’ visits, n = 4565 (composed of 49.2 % female visits)]. The visual depiction of the time series plots for each of the


Utilizing comprehensive records from all emergency departments in Ontario and Alberta (two provinces comprising approximately 50 % of the Canadian population) (Statistics Canada, 2019), the current study found no evidence that the implementation of the Cannabis Act was associated with significant changes in post-legalization patterns of all drivers’ traffic-injury ED visits or, more specifically, youth-driver traffic-injury ED presentations. Given that cannabis-legalization evaluation studies

Role of funding source

This research was supported by a Cannabis Research in Urgent Priority Areas Catalyst Grant (CU3-163011) from Canadian Institutes of Health Research (CIHR).


RCC conceived of the study, developed the research plan, organized the data acquisition, and prepared the initial and final manuscripts. MS contributed to the development of the research and analytic plans, conducted the statistical analyses, and helped to interpret the results and prepare the final manuscript. JVH, MA, TS, SM, BHP and SJK helped to interpret the results and prepare the final manuscript. All authors have read and approved the final manuscript.

Declaration of Competing Interest

There were no apparent conflicts of interest for the authors in relation to this work.


The authors would like to thank Amanda Farrell-Low for her editorial skill in the process of preparing the manuscript for submission. The Canadian Institute for Health Information provided the de-identified data utilized in the current study.

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