Cannabis decriminalisation doesn’t increase road traffic accidents, finds study

Cannabis decriminalisation is not associated with a notable increase in traffic accidents, finds a new report.

The report from the Canadian Institute of Actuaries (CIA) and the Casualty Actuarial Society (CAS) analyses the impact of cannabis decriminalisation on the vehicular accident experience in Canada and the United States. 

Previous studies have suggested that cannabis decriminalisation is associated with a higher number of drivers operating vehicles under the influence of the drug. As countries across the world make moves towards similar policies, more research is needed around the effects of cannabis on driving and road safety.

This study examined Canadian and US data from 2016–2019, including official reports on collisions of private vehicles and losses, fatal accidents and weather factors.

It did not detect any statistically significant impacts of decriminalisation on the car accident fatality rate, insurance claim frequency or average cost per claim, particularly over the long term.

The report, Assessing the Impact of Marijuana Decriminalization on Vehicle Accident Experience finds, based on insurance statistics, that there were no significant changes to the trend and seasonal variations in Canadian traffic accidents after the change in legal status. 

Similarly, the estimated state-wide effects of decriminalisation in the US do not show any consistent, significant results that would support a conclusion that decriminalisation led to an increase in road accidents or fatalities.

Temporal patterns of human activity (such as yearly, weekly and daily cycles) and inclement weather are said to be much better predictors of the vehicle accident experience than decriminalisation.

Author of the report, Dr Vyacheslav Lyubchich, Associate Research Professor at the University of Maryland Center for Environmental Science (UMCES), writes: “The literature review shows that while marijuana impairment affects driving behaviour, the behaviour is not always riskier; for example, slower speeds and longer following distances of impaired drivers have been reported. 

“The observational studies of road accidents report mixed results, most often not detecting significant effects, particularly in the long term.”

Overcoming limitations of previous research

The study overcomes the limitations and disadvantages of earlier research on the effects of cannabis decriminalisation by utilising novel data-driven methodologies and technological advancements in machine learning.

For each data source, statistical and machine learning models were chosen to account for different sources of variability.

Dr Lyubchich said: “The methods used in this research include improved statistical models, machine learning and other data science techniques. The models used high-resolution weather data to account for the effects of weather factors.”

The Canadian Institute of Actuaries (CIA) is the qualifying and governing body of the actuarial profession in Canada, which deals with the measurement and management of risk and uncertainty. 

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