Improvements needed to detect cannabis impairment in drivers

May 14, 2021

A new study by researchers at McGill University published in the Canadian Medical Association Journal shows that significant improvements are needed in Canada to detect cannabis impairment among drivers.

Specifically, the study results show that improvements are needed to ensure public safety and protect the rights of legal cannabis users. The results of the research show that legalization of recreational cannabis in United States jurisdictions may be associated with a small but significant increase in fatal motor vehicle collisions and fatalities. When extrapolated to the Canadian context, this translates to 308 additional annual driving fatalities.

“Whether this will actually play out in Canada is also another question,” said Windle, one of the study’s principal authors. “There’s circumstances in Canada that are different from in the states which could prevent potential increases.”

According to the study results, some of the shortfalls in terms of cannabis testing Canada are related to current measures and tools used for detecting cannabis-impaired driving.

Amendments to the Criminal Code in 2018 included new laws and testing regimes for drug-impaired driving, while the police can use a Standardized Field Sobriety Test or a Drug Recognition Expert Evaluation to determine potential impairment. However, researchers have expressed concerns over the validity of those tests.

In addition to such tests, police can now use oral drug fluid screeners to assess the presence of cannabis or other drugs, which may provide grounds for police to demand a blood sample.

Currently, drivers with a blood THC concentration of between 2 nanograms and 5 nanograms per millilitre of blood can face a maximum fine of $1000.

However, according to Dr. Jeff Brubacher, an emergency physician and associate professor in the department of emergency medicine at the University of British Columbia, these levels do not always accurately reflect impairment.

“The problem with the levels is that they don’t really correlate very well with impairment,” said Dr. Brubacher. “We researched the association between risk and levels and we found that people with levels less than five nanograms/ml were not at any increased risk of causing a collision. That was interesting because the lowest per se limit is two nanograms/ml.”

According to the results of the December 2020 Public Safety Canada report, the proportion of drug-impaired incidents has increased over the past 10-12 years, with cannabis being the most frequently detected drug among drivers. However, the report also showed that charges aren’t as common and convictions are less severe when compared to alcohol-impaired driving.

“There is a long-standing and continuing trend where charges are laid more frequently and lead to higher levels of convictions for alcohol than for drug-impaired driving cases,” the report states.

In her interview with CTV News, Windle said that although more research is needed to detect cannabis impairment, the current measures come with potential consequences. “If you exceed the legal limit, there are fines, there’s possible jail time for repeat offences and that is outside a determination of driving impairment.”