Canada’s 4/20 celebration of all things pot may be more festive than ever this year as partakers anticipate the laws legalizing marijuana coming this summer.

But a new study showing significantly increased traffic deaths on the April 20 “high holiday” is a sobering reminder of the dangers that marijuana — and freer access to it — could pose on the country’s roadways.

The study, co-authored by Toronto physician Donald Redelmeier, suggests the number of fatal accidents in the United States on 4/20 increase at magnitudes that rival those seen on drink-happy Super Bowl Sundays

And as the Bill C-45 cannabis legislation lumbers through the Senate, debate is also focusing on accompanying legislation that will set out testing procedures and penalties for “drugged driving.”

Indeed, heated arguments over the proposed Criminal Code amendment — known as Bill C-46 — have spilled out of the upper chamber to cause a kind of road rage between leaders of two prominent advocacy groups.

“The thing is, he’s full of crap,” says MADD Canada head Andrew Murie of a key opponent.

That opponent, John Conroy, president of the National Organization for the Reform of Marijuana Laws, known as NORML, says Murie “obviously doesn’t understand how (cannabis) works.”

The two embody the broader arguments over the bill — arguments that pit critical deterrence strategies against concepts of fairness and justice.

On the deterrence side, Murie says the main marijuana law will place the drug in the hands of untold more Canadians, some of whom will doubtlessly smoke or bake it and get behind the wheel.

Unexpectedly, this doesn’t frighten Murie — whose group has led the campaign against impaired driving for decades — nearly as much as the countervailing testing bill thrills him.

That bill will allow police forces to purchase and deploy oral fluid testers — so-called spit kits — that will accompany the familiar alcohol breathalyzer machines in tens of thousands of cruisers across the country.

These testers will screen for THC, the psychoactive component of cannabis, as well as for cocaine and methamphetamine.

The law will also define the levels of the drugs that will trigger a positive spit kit test, like the 0.08 blood alcohol content for booze.

For THC, Murie says the level has been set at 25 nanograms in oral fluid; for cocaine and meth it is 50 nanograms.

“Those are really high levels,” he says.

But they were set high, Murie says, so the devices could withstand the lawsuits that will doubtlessly challenge their veracity.

“For example, if it was set at five nanograms for THC, there might be a case where the reliability (of the devices) drops from maybe 98 per cent to 91,” he says. “So if you set it really high, you get the most impaired people.… Anyone who says they smoked yesterday, there’s not a chance in a million years they’re going to fail one of those tests.”

The roadside spit kits will simply deliver a pass or fail verdict. A failure will prompt further screens, likely in the form of a blood test at a nearby police station or clinic.

It’s here that the legal ramifications come into play, with a 2 nanogram THC reading in the blood prompting a summary conviction and five nanograms representing a criminal offence — with punishments in line with those for alcohol.

(Current impaired driving penalties include a $1,000 fine and a one year driving suspension with subsequent offences bringing longer license losses and jail time.)

There is also a booze-plus-pot provision which makes a combination of a 0.05 alcohol level plus 2.5 nanograms of THC a criminal count as well.

At present, police can only use roadside sobriety testing protocols — such as having suspect drivers stand on one foot — to judge cannabis impairment.

Toronto police, who helped test a pair of spit kits last year, charged only 69 people with a drug-related impaired driving offence in 2017. It has only “a few hundred” officers trained to preform the two existing forms of roadside sobriety tests, says force spokesperson Clint Stibbe.

While 50,000 drunk-driving charges are laid each year across Canada, fewer than 1,000 are handed out for drug impairments.

“Right now you can drive impaired by cannabis with very little fear of being caught and detected,” Murie says.

“This … is the most comprehensive legislation we’ve seen in the last 20 years. (It’s) very positive, very positive.”

Redelmeier’s study adds to the evidence that people high on pot do pose a significant threat on the roads.

A professor in the University of Toronto’s faculty of medicine, he says the coming marijuana legalization prompted his research into its potential to increase life-threatening traffic accidents.

“I already see far too much of them,” says Redelmeier, who practises at Toronto’s Sunnybrook Health Sciences Centre, home to the province’s largest trauma unit.

He says his 4/20 paper showed that deaths from traffic accidents after 4:20 p.m. that day — the festival’s traditional spark-up time — increased by 12 per cent compared with evenings a week apart over a 25-year study time frame that ended in 2016.

“And you might say ‘Gee Dr. Redelmeier, 12 per cent isn’t that high, after all July 4th (American Independence Day) is associated with about a 36-per-cent increase,” says Redelmeier, whose paper appeared in the journal JAMA Internal Medicine.

“But there the nuance is that almost every American celebrates July 4th whereas fewer than 10 per cent of Americans celebrate 4/20.”

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If 4/20 was celebrated at July 4th levels, traffic fatalities would see a 200 per cent increase, Redelmeier estimated.

And many of the drivers involved in the 4/20 fatalities — the data came from U.S. National Highway Traffic Safety Administration statistics — would have also consumed alcohol and other drugs, bringing the study in-line with real world partying practices, he says.

Redelmeier says the best science on the risks of driving with a marijuana high alone comes out of driving simulator tests, which generally show a doubling of accident risks.

Alcohol, on the other hand, was associated with a fourfold risk increase, he says.

Conroy, who has fought some of the most prominent marijuana rights cases in Canada, figures a new fight is coming over the drugged-driving laws.

“It’s definitely not going to survive a court challenge,” says the British Columbia attorney.

“How can you have people found guilty when they are not impaired? We do not want innocent people being convicted, either — do we?”

Conroy says many veteran dope smokers would be able to drive with undiminished skills at the rookie THC levels proscribed by C-46 because of their body’s greater tolerance.

“Now I’m not suggesting that people can’t be impaired by cannabis, certainly we need to be concerned about novice users and intermittent users for sure,” he says.

But at two to five nanogram levels he says “huge numbers of people are going to have that present and not be in the least bit impaired.”

There is also the question of medicinal users, who would typically have elevated THC levels most or all of the time, Conroy says.

He points to one of his clients — a motorcycle accident survivor — who is only able to walk and talk with confidence because of his profound marijuana consumption.

“He would be more dangerous on the road without cannabis than with because of his chronic pain,” Conroy says of the client, who has been cleared to drive by B.C.’s provincial insurance corporation.

“And he’s not the least bit impaired because he’s developed such a huge tolerance to it.”

Conroy says challenges decades ago to federal Criminal Code blood alcohol levels caused some provinces to move the drunk-driving laws to their highway traffic acts, where a simple positive reading triggered penalties.

In England, where drugged-driving laws have been on the books since 2016, prosecutors need not prove impairment, just that the driver was over similar limits for penalties to kick in.

But Murie says Conroy is only concentrating on the law’s relatively low THC blood levels and is leaving out the 25 nanogram roadside limit, which he says would leave anyone “grossly impaired.”

Other toxicology experts contend that Murie is being hyperbolic with his pronouncements, and that 25 nanograms would not be enough to impair many veteran tokers.

Amy Peaire, chair of the Canadian Society of Forensic Science’s drugs and driving committee, told the Star she is not at liberty to discuss issues surrounding the upcoming bills.

But Peaire — whose committee is advising the federal government on the driving laws and oral fluid devices — told a Senate hearing earlier this year that, unlike alcohol, there are no proven links between THC blood levels and impairment.

Robert Mann, a senior scientist and impaired driving expert at Toronto’s Centre for Addiction and Mental Health, says the 25 nanogram roadside threshold is likely a good indication of high THC content in the blood and of impairment.

Even for those who may not be impaired, Mann points out that driving is a privilege, not a right. And, he says, if people are going to drive on public roads, they must accept doing so under government-set THC limits that would leave many, or most, unable to drive safely.

“We owe it to ourselves and other road users to drive safely and to avoid taking risks that could cause grievous harm.”

Conroy does not dispute that breathalyzer tests and RIDE programs have helped drastically cut drunk-driving carnage. But he maintains that such deterrence can be replaced with other measures as the country enters a relative marijuana free-for-all.

“I think education and a lot of it and a lot of publicity in terms of it is the way to go.”

That may be the only thing on which he and Murie agree.