Before a driver who had just smoked a lot of pot hit the vehicle Nancy Stewart's husband was driving, killing him instantly, she hadn't given much thought to the dangers of someone getting behind the wheel while impaired by drugs.

Doug Stewart was killed and his daughter Emily seriously injured after the vehicle he was driving was struck by a driver who had just smoked a lot of marijuana. (Nancy Stewart) "To be perfectly honest, I'm not sure it was on my radar," says Stewart, whose husband Doug died in the crash on his way home to Oakville, Ont., from his mother's 80th birthday party.

The Stewarts' daughter Emily was with him, and suffered a catastrophic brain injury.

"I think drinking and driving is on a person's radar," adds Stewart. "I didn't do drugs, nor [did] any of our friends, so [drugged driving] was sort of a non-issue. I think about it a lot now."

Driving while impaired by drugs has been illegal under the Criminal Code for nearly a century, but is rather problematic to enforce.

Some legal changes have focused on trying to give police better ways to detect drug-impaired driving at the roadside.

'Not a simple problem'

But for many observers, there is still a long way to go in addressing an issue that is fraught with scientific and legal challenges, and which does not share the same social stigma as drunk driving.

"It's certainly not a simple problem," says Doug Beirness, a senior research associate for the Canadian Centre on Substance Abuse.

"People who might otherwise get involved shy away because it is so complex, and there's no easy answers."

We need to know how to test them best first and what's the best technology that's going to get us there. - Doug Beirness

While there may be no easy answers, some figures suggest it is a problem on the rise.

Testing of drivers involved in fatal crashes is inconsistent across Canada, but one Canadian Centre on Substance Abuse study found that the percentage of drug-positive drivers rose from 29.7 in 2000 to 36.7 in 2008.

Figures from Statistics Canada show that the number of people charged by Canadian police forces with drug-impaired driving offences, including impaired operation causing death or bodily harm, along with impaired operation of a vehicle, vessel or aircraft, rose from 183 in 2008 to 1,159 in 2013. (Over the same period, the number of people charged with impaired driving fell from 65,822 to 53,944.)

For drugged driving, the essence of the challenge lies in finding the best way to test drivers, Beirness suggests.

"We need to know how to test them best first and what's the best technology that's going to get us there."

Next best after blood

And for that, it's not as easy as alcohol, which can be detected initially in a driver's breath very quickly.

"With any drug, you need blood," says Beirness. "Now the alternative, the best alternative, is oral fluid. It's not quite as easy, it's a little bit more intrusive, it's not quite as quick."

A breathalyzer gives police officers an easy roadside way to test for alcohol, something that is not as easy to do for drugs. (Darryl Dyck/ Canadian Press) And given that there are hundreds of drugs, the prospect of testing for each one seems daunting, if not impossible. Some drugs also affect different individuals differently.

But some drugs do turn up more often than others.

"The No. 1 drug that people use recreationally besides alcohol is cannabis," says Beirness. "That's the one you find most in drivers and we're getting pretty good at measuring and testing for cannabis now."

But measuring and testing are one thing. Finding a way to determine what would be the critical level — a parallel to the long-established levels that legally determine impairment by alcohol — is proving trickier.

"You have to do the research to be able to determine what the most appropriate limit is for each and every substance that could possibly impair driving," says Beirness.

"That's a daunting task. It took us 50 years to come up with the level of 80 [milligrams of alcohol in 100 millilitres of blood] for alcohol. We don't have the time to do that."

Better detection tools

One long-awaited study looking at oral fluid level tests and levels of drugs that could constitute impairment is being conducted by the Canadian Society of Forensic Science's Drugs and Driving Committee.

The federal Department of Justice is looking forward to seeing the report and at that point will examine its conclusions, a spokesman said via email.

Legislation in 2008, introduced in the Tackling Violent Crime Act, "gave police tools for better detecting drug-impaired driving at the roadside and through drug evaluations by a trained officer at the station," the spokesman said.

Such testing, however, is expensive and not always easily accessible across Canada.

"Because so few officers are trained in it, they're generally not available," says Andrew Murie, chief executive officer of MADD Canada.

Other jurisdictions outside Canada have broached the subject.

Murie points to Britain, which introduced legislation in March making it illegal to drive if a person has certain drugs above certain levels in the blood.

The new law covers 16 legal and illegal drugs, including cocaine, ketamine, ecstasy and cannabis. Police will also be able use a "drugalyser" testing device at the roadside to screen for cannabis and cocaine, the BBC reported.

'Really good things'

"They've done a lot of really good things with their legislation," says Murie.

"Most of Europe uses it. Germany and various countries like that. Australia uses it as well. There's way more countries that are doing it than not."

Driving after smoking marijuana doesn't carry the same social stigma as getting behind the wheel after drinking alcohol. (Mel Evans/Associated Press) Back home, however, while research continues, the issue seems somewhat adrift legally and politically.

"I think what everyone is looking for is some federal leadership because it's such a complicated issue," says Beirness.

"You need someone to stand up and grab it and say we're going to take the lead on this one … [and] do whatever we can to help the provinces and the police and whoever else needs to be involved in this and I don't see this happening," says Beirness.

There's also the question of the amount of social stigma around drugged driving, which so far does not rival the negative public perception that has grown around drunk driving.

"It's taken us well over 30 years really to get to the point where you can talk to just about anybody and they will say drinking and driving is not a good thing," says Beirness.

What can the police do?

When it comes to drugs and driving, people do say it's a bad thing, you shouldn't drive after such-and-such a drug, he adds. But younger Canadians don't think cannabis is harmful and think even if they do get stopped by police, "the police can't do anything about it."

"So we've got a long way to go there."

Stewart just wants to see progress, through laws, more equipment to test drivers and more education.

"I'd like people to take it seriously and realize that the word is in fact impaired driving and it's not just drink, it's also drugs as well. Let's face it, driving is a dangerous thing. "

The driver who hit her husband "was not thinking," Stewart says, "not realizing the seriousness of how quick it is that your life or the life of another person can be taken … and it has repercussions that last forever and run so incredibly deep.

"It's something that I will never ever recover from, nor will our family."