Impaired driving has been around as long as people have been motoring. The first arrest for drunk driving was in 1897, long before any lab testing could be done. For decades, the issue of impairment while driving was ignored or under-appreciated. Drunk driving was commonplace and there were no regulations to prevent such actions. After countless deaths (including Gone with the Wind author Margaret Mitchell), efforts were made to quantify how drunk one could be while still getting behind the wheel of a car.
Per se laws represented a revolution in case law: The presence of alcohol in the blood above a certain level was sufficient to establish criminal impairment by proxy.
Where to draw the line? Different nations have adopted different standards. In establishing a blood limit for alcohol, the US initially selected a level of 0.15 (0.15 g of alcohol per 100 mL) then decreased it to 0.10, still higher than virtually all other developed nations, due to a combination of factors including spread out geography, alcohol industry lobbying and American libertarianism. Canada did not see per se laws introduced until 1969, when it became criminal to drive with a BAC of 0.08 or greater. Individual provinces have introduced additional penalties for drivers who are above a 0.05 limit.
Per se laws represented a revolution in case law, because no longer was it necessary to prove that the driver was unfit to drive at the accident or that the driver was impaired due to the alcohol rather than fatigue or medical infirmity. The presence of alcohol in the blood above that level was sufficient to establish criminal impairment by proxy. This has remained controversial, but the science is strong enough for the courts to have accepted this legislation.
Cannabis and Per Se Laws
As legalization of recreational cannabis looms over Canada, there have been public concerns about cannabis and driving, and how to regulate impairment from cannabis in the same way that we regulate impairment from alcohol. Both national and provincial governments in Canada have included per se limits within their legislation. Driving with a blood THC level greater than 5 ng/mL will be a federal crime, punishable by up to 10 years in prison. Driving with a blood THC level between 2 and 5 ng/mL is a summary offence with up to $1000 fine. Individual provinces have additional restrictions—Quebec is proposing a zero-tolerance policy.
Why do per se laws work for alcohol but not for cannabis? The primary reason is that alcohol and cannabis are different drugs.
However, there’s a problem with introduction of per se laws for cannabis—they aren’t based on good science.
As the US Department of Transportation put it in its 2017 National Highway Traffic Safety report, “A number of States have set a THC limit in their laws indicating that if a suspect’s THC concentration is above that level (typically 5 ng/ml of blood),…