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Canadian Study Finds No Increase in Traffic Accidents After Cannabis Legalization

By Alexander Beadle

Published: Nov 22, 2021   
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Cannabis legalization in Canada has not led to any associated increase in the number of traffic accident injuries, a new study has found.

Looking at data from Alberta and Ontario – the two Canadian provinces with the most cannabis stores and the only two to report all emergency department visits – researchers found no statistically significant differences in the number of traffic-injury emergency department visits before or after Canada’s nationwide cannabis legalization in 2018.

The study, authored by researchers at the University of Northern British Columbia, the Centre for Addiction and Mental Health (CAMH) in Toronto, University of Victoria, and Dalhousie University, was recently published in the journal Drug and Alcohol Dependence.

Legalization not associated with a change in traffic accidents

Using provincial emergency department (ED) records from between April 2015 and December 2019, the researchers used statistical models to assess whether there were any associations between Canada's cannabis legalization (taken as October 17, 2018) and the weekly provincial counts of traffic-injury presentations recorded at the ED. In total, more than 239,000 reports on ambulatory patients were screened for analysis.

“Implementation of cannabis legalization has raised a common concern that such legislation might increase traffic-related harms, especially among youth,” Dr Russell Callaghan, a UNBC professor and the study’s first author, said in a statement. “Our results, however, show no evidence that legalization was associated with significant changes in emergency department traffic-injury presentations.”

The study examined associations across two groups: all drivers, specifically young drivers in Alberta (aged 14-17 years) and Ontario (aged 16-18 years).

There were small increases found in the number of ED visits for all drivers, and a small decrease for young drivers in Alberta. However, none of these differences could pass the threshold of statistical significance. As a result, the research authors concluded that the “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.”

Strong drug-impaired driving laws may have been a deterrent

These findings are contrary to trends that have been observed across the border in the United States. One study published earlier this year examining trends in fatal motor accidents revealed a “small but significant increase” in fatalities following the legalization of recreational cannabis in some states. A second study published in 2019 assessed traffic accident fatality statistics in three states with legal recreational cannabis use – Colorado, Washington State, and Oregon – and compared these statistics to their neighboring states. A small, though temporary, increase in fatalities per million residents was also seen here.

“Our findings are somewhat surprising,” Dr Callaghan admitted. “I predicted that legalization would increase cannabis use and cannabis-impaired driving in the population, and that this pattern would lead to increases in traffic-injury presentations to emergency departments.”

“It is possible that our results may be due to the deterrent effects of stricter federal legislation, such as Bill C-46, coming into force shortly after cannabis legalization. These new traffic-safety laws imposed more severe penalties for impaired driving due to cannabis, alcohol, and combined cannabis and alcohol use,” he explained.

Bill C-46 was introduced in 2017 to strengthen Canada’s existing drug-impaired driving laws. As well as increasing the penalties for some drug-impaired driving offences, Bill-46 also allows for law enforcement to make use of roadside drug testing kits if the police suspect impairment. While there is some uncertainty over the effectiveness of roadside tests for THC, the fact that the public is aware of roadside testing being a possibility may be serving as a general deterrent from driving under the influence of cannabis.

Driving under the influence

Improving roadside detection tests is an obvious priority for cannabis researchers looking to address drug-impaired driving. But researchers are also interested in exactly how cannabis might affect those who do get behind the wheel.

“Just because cannabis is legal and more people are consuming it doesn’t mean significantly more people will be driving impaired,” study co-author Scott Macdonald, a scientist with the Canadian Institute for Substance Use Research at the University of Victoria and author of the book Cannabis Crashes: Myths and Truths, told the Vancouver Sun.

“Being stoned from marijuana is also very different from being impaired from alcohol. While both present safety risks, being drunk is more dangerous,” he said. “People who are stoned can have memory issues and divided attention, making it difficult for them to do two things at once, but being drunk affects a person’s actual psychomotor performance and can lead people to drive more recklessly.”

Indeed, one study comparing drivers under the influence of cannabis versus alcohol found that those who were cannabis-impaired were generally more aware of their impairment than the drunk drivers, and thus were more able to compensate when given complex tasks to execute.

However, a literature review comparing multiple studies on drunk and drug driving found that while the drunk drivers had poorer cognitive function, their psychomotor skills were only significantly disturbed when highly intoxicated. In contrast, the drivers under the influence of cannabis generally had very poor attention spans and worse time-critical motor function, resulting in a tendency to drive dangerously slow. The review concluded that “it is very difficult to decide which drug is more dangerous” with the characteristics of the driver also playing an important role.


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