Two decisions Parliament will have to make about pot-impaired driving

At some point in the next year or two, recreational pot will be legal in Canada.

With easier access to marijuana — including edibles — in general, more people will consume pot in some form. A federal study in November put the number of new marijuana users under legalization at around 600,000.

Unavoidably, as well, more Canadians will smoke, or ingest, and drive.

Stoned driving raises many of the same problems as drunk driving, and may be nearly as deadly. Marijuana is the second-most common drug, after alcohol, found in the bodies of drivers who die in crashes.

And it’s becoming more common. In 2015, twice as many Ontario residents reported driving after using cannabis as did in 2010, according to the Centre for Addiction and Mental Health in Toronto (CAMH). The report shows that 5.6 per cent of men and 7.6 per cent of people between 18 and 29 admitted driving after using marijuana.

It seems to make sense to treat stoned driving like drunk driving. Law enforcement across the country has a well-understood system for drivers suspected to be under the influence of alcohol. To get there, lawmakers will have to make decisions about how to deal with people who toke and drive.

1. Whether to set legal bloodstream limits for marijuana, as we do for alcohol

For drugs other than alcohol, Canada uses an “effects-based” enforcement system, which tries to measure a driver’s level of impairment by administering a complex series of tests. The approach lacks the clarity of testing for alcohol impairment, and the actual testing is time-consuming.

As well, the courts often don’t accept the results. In a Saskatchewan case in 2012, a driver was acquitted despite what a police officer described as an “an overwhelming odour” of marijuana in her car, and admitting to smoking pot. 

In mid-October of this year, the Supreme Court heard arguments in the case of an Ottawa man convicted of impaired driving under an effects-based system. The decision, which hasn’t been issued yet, may point the way to a more usable system — or throw out the existing one entirely.

READ: What happens when you’re caught driving stoned? Canada’s Supreme Court may soon tell us

An alternative to the “effects-based” enforcement system is a per se system, which sets legal limits for levels of a substance in the blood, as we do with alcohol. It may also be easier to enforce.

“There are studies out there that show that that increase, that elevation in risk, increases with higher THC levels. That research is pretty clear, and it’s pretty widely accepted,” explains Robert Mann of CAMH.

It’s possible to make per se laws for marijuana or any other drug, and a number of other jurisdictions including Britain, some U.S. and even Australian states have done so.

(Last year, Britain set legal blood limits for 17 different drugs, many of them illegal.)

The legal limit for pot, in places that have set one, is expressed in micrograms (millionths of a gram) of THC per litre of blood. It looks like this: µg/L.

While a blood alcohol content of 0.08 is an internationally accepted point at which a driver will be charged with alcohol-impaired driving, pot limits vary wildly. Britain’s is 2µg/L, while in Colorado and Washington state, where recreational marijuana is legal, have set 5µg/L.

READ: Government predicts legal pot will lead to influx of lab tests

“I think that would be better than the current scheme, which scientifically has its challenges,” says defence lawyer Theo Sarantis. “It would be a vast improvement.”

Jonathan Rosenthal, also a defence lawyer, disagrees. (Both often defend people accused of impaired driving.)

“I don’t see this per se stuff coming for a long time,” he argues.

“(Marijuana) affects everyone differently, unlike alcohol, where we know, at a particular baseline, everyone’s ability is impaired. For example, a very experienced drug user may show different signs than someone who’s using it for the first time. Some experts will say that an experienced user needs less of it to get the same effect.”

WATCH: Ottawa is expected to legalize marijuana this spring, and that is raising concern about road safety and drugged driving.

1:47 Education on drugged driving key leading up to marijuana legalization says CAA

Other jurisdictions have taken a zero-tolerance approach for any level of the drug, but courts have tended to acquit drivers whose only offence was testing positive for any level of marijuana, illegal or not, without evidence of impairment. (Earlier this year, an Australian court acquitted a driver who had failed a roadside saliva test nine days after he’d last smoked pot, and Arizona’s Supreme Court made a similar decision in 2014.)

2. Whether saliva tests are good enough to stand up in court 

Breathalyzers give police a roadside tool for testing drunk drivers that’s easy to use and accepted by the courts.

The equivalent for marijuana, so far, is a saliva test used to screen drivers for THC. They’re widely used in Australia, but at least until recently they haven’t been as reliable as tests for alcohol.

Although Dalhousie University professor Mark Asbridge was critical of the tests in 2014, telling a House of Commons committee that “we don’t have very good roadside testing technologies,” he is more positive now.

“They … are reliable at detecting the presence of a drug, and the devices and tests are well regarded and accepted in the countries that use them,” he wrote in an e-mail to Global News.

READ MORE: Police testing roadside devices to detect drugs

Mothers Against Drunk Driving CEO Andrew Murie agrees.

“The quality of the instruments is getting a lot higher. If you look at a study that was two or three years ago, the instruments are much better today.”

A system for marijuana-impaired driving that involved per se limits and was enforced with saliva testing could be set up right now, Murie argues.

“There’s nothing that stops the government today, if they wanted to, from introducing that legislation and putting those things in place.”

The only real complication is that THC leaves the body more quickly than alcohol, making quick testing a necessity, he says.

In recent testing of four saliva testing systems, however, three out of four gave significant numbers of false positives for marijuana. And earlier this year police in Australia reported problems with false negatives with their system.

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A Colorado police officer demonstrates an oral fluid drug screen testing device. (Getty Images)

“With alcohol we have technologies that are easily used to measure the amount of alcohol in your body, and with cannabis that’s much more difficult,” CAMH’s Mann explains.

“The measurement is a challenge, because on the one hand for alcohol, for example, you just need a simple breath test with equipment that’s been developed for the last 50 years, whereas with THC, blood is the gold standard.”

But it’s one thing to blow into a machine, particularly if there are penalties for refusing — quite another to face a police officer brandishing a needle.

On the other hand, some jurisdictions have gone there:

“In Arizona they train police officers to be phlebotomists,” Mann says. “That’s also the case in some European countries as well.”

“I doubt that that’s something that Canadians would particularly supportive of.”

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The reliability of testing is something Canadian courts will have to wrestle with if saliva tests are adopted, Sarantis says.

Defence lawyers in marijuana-impaired cases will challenge any testing system in detail, as they’ve done for many years for alcohol testing.

“How reliable these things are, what kind of testing has been done, can we depend on these things before we subject somebody to being arrested, criminally prosecuted, taken to a jail cell, and ultimately facing a criminal conviction. We’d have to know more about how accurate these things are.”

The federal commission studying the details of pot legalization has flagged the need for better roadside testing for marijuana. Marijuana-impaired driving is a priority for the commission, chair Anne McLennan said last week.

The commission has finished its report, which will be made public in mid-December.

Many people have tried marijuana only to find it was far more powerful than they expected. Someone planning to drive can keep their alcohol consumption to a very conservative level, but for an inexperienced user it’s much harder to do that with pot.

But the fact that you found yourself much more stoned than you expected doesn’t help if you’re facing an impaired charge, Rosenthal warns:

“That wouldn’t give you a defence. If you voluntarily consume drugs it would be pretty hard to say ‘I didn’t know that marijuana was that strong.’”

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