2025-06-12 –, BS 3.16 - 60 cap.
Objective. Cannabis use impairs motor vehicle operation, yet its broader effects on traffic collisions following legalization remain unclear. This study evaluates the impact of Canada's Cannabis Act (CCA) (2018), regulating non-medical cannabis use, on traffic collisions in Quebec, focusing on overall, alcohol-related, and drug-related collisions, and incorporating data on monthly cannabis sales.
Methods. We conducted interrupted time-series analyses using Poisson regression to examine daily traffic collision rates (overall, alcohol-related, and drug-related) per annual average daily flow (AADF) in Quebec from 2015 to 2022. The AADF, representing the average number of vehicles passing a given location daily, was used as the denominator in rate calculations. Analyses were performed in five major cities: Montreal, Quebec City, Sherbrooke, Laval, and Longueuil. We investigated associations between the CCA’s implementation and cannabis sales (measured in kilograms sold per month per population) with changes in collision outcomes. Meteorological factors (e.g., temperature, precipitation) and non-pharmaceutical public health measures during the COVID-19 pandemic were controlled for.
Results. The associations between cannabis-related policies and collisions were evaluated using Incidence Rate Ratios (IRRs). In Montreal, cannabis sales were associated with a non-significant increase in overall collisions (IRR = 1.005, 95% CI: 0.988–1.023). In Quebec City, cannabis sales were linked to a similar non-significant increase (IRR = 1.012, 95% CI: 0.966–1.031), and in Sherbrooke, the trend persisted (IRR = 1.007, 95% CI: 0.987–1.028). Laval also experienced a non-significant increase (IRR = 1.015, 95% CI: 0.978–1.033), while Longueuil showed no change (IRR = 0.900, 95% CI: 0.740–1.092). For drug-related collisions, Montreal showed a non-significant increase (IRR = 1.015, 95% CI: 0.958–1.053), and Quebec City exhibited a non-significant decrease (IRR = 0.990, 95% CI: 0.942–1.022). Similar trends were observed in other cities, with no significant associations identified for either drug- or alcohol-related collisions.
Conclusions. The CCA in Quebec does not appear to have significantly altered overall, alcohol-, or drug-related traffic collision rates. These findings suggest that other factors, such as enforcement, should be studied to better understand the full impact of the CCA.
José Ignacio Nazif-Munoz, PhD, is Assistant Professor at the Faculty of Medicine and Health Science at Université de Sherbrooke, Québec. He holds a researcher-fellowship Junior 2, from the Fonds de recherche du Québec – Santé and the CRMUS Chair on the Evaluation of Public Policies Governing Alcohol and Cannabis Consumption in Quebec. His research interests lie in the intersection of sociology, substance use, and epidemiology with attention to public policy evaluation tools and their effects on vulnerable populations. He is advancing new research questions regarding the consequences of cannabis liberalization policies. He has more than 60 peer-review articles on high-impact journals such as Addiction, International Journal of Drug Policy, Epidemiology, Punishment and Society and Child Abuse & Neglect.