As Canada's legalization of cannabis approaches, and we continue to be inundated with articles and opinion pieces on the various implications (see my piece on Is Canada's legalization of cannabis actually a big deal?), more questions are being asked about how it will be possible (or not) to police driving under the influence of cannabis.
Canadians are clearly worried about the issue: a recent survey shows that a large majority know that cannabis reduces reaction times and the ability to concentrate while driving (although 9% inexplicably believe that cannabis makes them a better and more careful driver!), and a similarly large majority agrees that driving under the influence of cannabis is no less dangerous than driving under the influence of alcohol, and that people often don't realize that they are driving impaired by cannabis. Other research shows that about one in 7 Canadian cannabis users admit to having driven within 2 hours of usage within the last three months. Men are twice as likely as women to drive while high, and daily users are about 4 times as likely to do so as occasional users. Some 1.4 million Canadians have been driven by someone who had consumed cannabis in the previous 2 hours. And all of that's BEFORE legalization!
The science (driving simulations and on-road experience, cognitive tests, and crash collision statistics) certainly agrees that driving while high IS a problem, despite any number of anecdotal reports to the contrary. For non-daily users, who do not have a baseline blood level of THC already, it takes about 6 hours for the effects of one joint to dissipate. A "15 minute pause" as many people suggest is therefore clearly not going to be much use.
Granted, regular cannabis smokers may be more aware of their impairment status than are drinkers, and crash statistics suggest that drinking is a much greater hazard than joint-smoking as regards road accidents, but the risks (to the smokers and to others on the road) should not be down-played. Cannabis users are typically more cautious drivers than are drinkers, but they still tend to weave around on the road in much the same way, and are much less likely to be able to react to emergency situations than sober drivers. Cannabis combined with alcohol (a common practice) is a particularly lethal cocktail.
Part of the problem in policing marijuana use is the establishment of legal limits. The Canadian government is using 2 nanograms of THC per millilitre of blood as the limit for a summary conviction (a fine of up to $1,000), and 5 ng as a criminal offence punishable by up to 10 years in jail. This is roughly in line with other jurisdictions that have legal cannabis. But, unlike in the case of alcohol, it is not clear to people how many joints or show many puffs that means: it depends on how deeply the smoke is inhaled, the strength of the cannabis, the person's size tolerance and experience, etc. Cannabis in the form of lotions, candies, edibles and drinks presents even more of a challenge.
Even a person's THC blood levels is not always a reliable indicator of impairment, and this is further complicated by the fact that blood levels of THC tend to fall quite quickly after smoking, and then flatten out, although the THC remains in the brain for much longer, so a smoker may feel (and act) high even though their THC levels are relatively low. Some countries, like New Zealand, don't even use a THC reading to prove impairment, relying instead on a subjective assessment if the evidence for impairment (although this has its own drawbacks).
In Canada, the police are likely to employ initially a three-part sobriety test - walk in a straight line, balance on own foot, track a finger - as they do now, before legalization. If a blood test IS required, though, it needs to be administered relatively quickly, because THC levels, as has ready been mentioned, tends to fall quite quickly. A proposed saliva test is still not approved, and may not be distributed to law enforcement officers in time for the "launch" of the new law in October 2018.
The whole issue is fraught with challenges and, although many of these challenges exist even now, before legalization, you can bet that they will become substantially magnified after October. The subsidiary issue of cannabis impairment in the workplace is a whole other ball game, and companies are scrambling to adjust corporate policies to accommodate it. What a monster the government may be in the process of creating!
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