Taking the high road: Cannabis users underestimate driving risk

Despite growing evidence, many cannabis users believe their driving is not impaired by the drug, and may even be improved by it. The fatal impact of those beliefs is being felt by families all too often.

By JASON WALLS

In the early hours of July 13, 2005, 19-year-old Trent Nathan King was returning home after dropping off a friend in Melbourne’s east. Also in the car were 18-year-old Michael Rendall and Ashley Pearce, 17.

The evening had been spent at Rendall’s house, where the group had been drinking, though King, who was driving, had abstained.

At about 1am, King’s BMW was approaching the intersection of Evans and Thompsons Rd in Cranbourne West when he failed to stop at a give way sign and was struck by a Mitsubishi truck entering the intersection from the other direction.

The driver of the truck later testified in court that he saw the BMW out of the corner of his eye, and despite having slowed because of an approaching train line, was unable to stop in time to avoid a collision.

“By the time I took my foot off the accelerator and go to put it on the brake, I’d already hit them,” he said.

When paramedics arrived a short time later, they discovered King lying in the middle of Thompsons Rd screaming and yelling incoherently, the BMW upside down in the bushes.

King spent almost a month in hospital recovering from his injuries, while Rendall and Pearce did not survive theirs.

Forensic experts later determined that, despite having avoided alcohol that night, King had ingested cannabis in the hours before the crash and retained levels of the drug in his blood that would have impaired his ability to properly control the vehicle.

He was convicted of culpable driving in 2008 and sentenced to seven-and-a-half years in prison.

World-first initiative on drug screening

Also in 2005, Victoria Police began ramping up their roadside drug detection program, introduced the previous year when Victoria became the first jurisdiction in the world to do so. Police screened 13,158 drivers in 2005, returning 300 positive results.

From 2006 until 2009 (the most recent figures available) the number of drivers screened rose steadily year on year, while those returning positive readings fell from 1.75 per cent to just over 1 per cent. Meanwhile, the number of road users killed as a result of targeted drugs (cannabis, MDMA/ecstasy, and methamphetamine) also reached its lowest point since 2001.

One conclusion is that the current zero tolerance policy is having the desired effect, however 1 per cent does represent 297 drivers who fell foul of the law in 2009.

And there is growing evidence – presented by the Australian Institute of Criminology in a research brief released last year – to suggest that many regular cannabis users are wildly underestimating the risks involved in driving while under the influence.

For every driver caught, there are others who aren’t, and those drivers screened out through roadside testing may only represent the tip of a much bigger problem.

In the latest National Drug Strategy Household Survey, conducted by the Australian government’s Institute of Health and Welfare in 2010, nearly one fifth of users reported having driven while under the influence of illicit drugs in the previous 12 months.

The same year, a NSW study found that nearly 80 per cent of regular cannabis users reported driving while high at least once in the past 12 months, including 27 per cent who did so “as frequently as once a week or more”.

These figures are illuminated by the results of a 2008 study of police detainees, in which the majority reported a belief that cannabis had no impact on their driving ability, with some even reporting a positive effect.

While Trent King’s own assessment of the risks he was taking on that night in 2005 may never be known (he told police he had no memory of the events leading up to the crash), his actions are a sobering reminder of the potentially deadly consequences of the attitudes represented in the research.

Questions on the science

Free Cannabis Party president Matt Riley is a long-term cannabis user who is far from convinced of the dangers of smoking and driving. He doesn’t believe laws that target cannabis use among drivers make sense, and questions their scientific basis.

“I think people have just made the assumption that because alcohol causes a problem with driving then cannabis automatically is going to, which I think is a bit silly,” he said.

Echoing the respondents in the 2008 study, Mr Riley even goes as far as to suggest that, in regular users, smoking cannabis may even improve driving ability because of a tendency to drive more slowly and carefully, while taking fewer risks than other drivers (one participant in a 2000 study reported feeling safe behind the wheel because he drove “like an old lady” when stoned).

“There's car insurance companies in Colorado and Washington [where recreational cannabis use was recently legalised] that offer discounts for medical marijuana card holders because they know that people with THC [the active component of cannabis] in their system have less accidents,” he said.

When pressed for a source for these claims, Mr Riley could only point to a single study, conducted by an online car insurance quote provider, which “seeks to dispel the thought that ‘driving while stoned’ is dangerous”.

The website has not made the study or its methods available publicly, but in a press release  the company’s CEO, James Shaffer, defended the view.

“The hypocrisy of it all is that if you get caught driving under the influence of marijuana, you will be fined and perhaps thrown into jail. What’s worse is that your insurance rates will definitely increase due to the traffic violation,” he said.

“What law enforcement agencies and insurers do not understand is that driving while high is actually a safe activity. I guess the key to safer driving is to use marijuana, but to do it under wraps.”

Head of Forensic Scientific Services at the Victorian Institute of Forensic Medicine Professor Olaf Drummer has been researching the links between cannabis and road trauma for over a decade. He said his work had shown a strong correlation between the two, and that regular use was far from a guarantee of a lack of impairment.

“In Victoria it's [involved in] around 15 or so per cent [of fatalities] and it's even a bit higher percentage of injured drivers … so it certainly is, after alcohol, the second-most common impairing drug found in drivers,” he said.

“So yes, you may well be a heavy user, it doesn't mean heavy users aren’t impaired, they are impaired, [even though] they might not be impaired to the same degree, if they use the same amount, as an occasional user.”

Further studies by the University of Adelaide’s Centre for Automotive Safety Research support this view, and research fellow Matthew Baldock provides a possible explanation for the discrepancy between the established risk and users’ perceptions.

He said that while cannabis use was not associated with the recklessness observed in people affected by alcohol, any inference that this meant driving while under the influence of cannabis was therefore safe, was false.

Instead, he said the impairment relating to cannabis use came from factors such as difficulty focusing on two things at once, increased risk of distraction, and an inability to drive in a straight line.

“The effect of cannabis is more on your performance, your ability to actually perform the task well and safely, rather than creating the recklessness that often comes with alcohol,” he said.

“The thing about driving is, everyone when they drive will make mistakes and do things not quite so well and it’s very, very rare that that leads to a crash. So the feedback you get from driving is – when you make an error usually nothing happens, and so we tend to feel very safe when we drive even if we're not driving very well.

“So people who smoke a lot of cannabis and drive very often on cannabis will get the feedback from their driving that, you know, ‘I do this quite often and I tend not to have a crash’ and they're sort of unaware that the whole time they actually have a higher risk of being involved in a crash.”

The rules on drugs and alcohol 

The disconnect between user attitudes and statistical evidence may also be partly explained through questions of legitimacy. Victoria’s “zero tolerance” drug-driving laws mean that drug users are treated differently to drinkers – who are free to have one or two drinks and then drive home without risking a fine – despite alcohol’s own prominent overrepresentation in crash statistics.

The argument goes that since it is illegal to drive with even tiny amounts of a proscribed drug in your blood (and in the case of cannabis these can remain present for days or even weeks), users can be stung even if they do the right thing by waiting before getting behind the wheel, leading them to feel unfairly singled out.

For his part, Free Cannabis Party’s Matt Riley believes the law discriminates against heavy users who would effectively maintain trace amounts of the drug in their system at all times, without necessarily being impaired.

Mr Riley, who has suffered from depression and anxiety, considers himself a “medical cannabis user” and compares the zero-tolerance approach to cannabis with prescription drugs, which aren’t routinely tested for.

“It automatically means that anyone who uses cannabis is excluded from having a driver’s licence,” he said.

“It would be like saying ‘Okay, anyone who's on antidepressants is not allowed to drive’, you know, ‘Okay, you've got depression, let's help you out by banning you from driving’.”

With these arguments in mind, an expert panel on drug-driving last year recommended to the UK Transport Department a threshold of 5ug/ml for establishing a legal driving limit (since adopted by Colorado legislators), bringing the laws into line with those targeting alcohol, but even this approach is controversial.

Unlike alcohol, there is no easy measure of cannabis intoxication akin to standard drinks, and users who may be completely unimpaired can still potentially return relatively high readings.

Prof Drummer acknowledges that the relationship between THC blood concentration and impairment is much more variable than with alcohol.

“We know that cannabis impairs, and the more you take the more you’re impaired,” he said, but in terms of setting a limit “it’s very hard to come up with a number”.

But what isn’t widely known, and despite the zero tolerance message, is that the current testing regime already comes with built in accommodations for this margin of error.

“The devices that [police] use to do the initial testing are not so sensitive that it will pick up really trace amounts. For example if somebody had used some cannabis the day before, they wouldn't be picked up today, even if they're really heavy users,” Prof Drummer said.

“So there is a protection for them, even though there is [ostensibly] a zero tolerance approach to cannabis.

“The reality is that … they’ll need to have [had] a fairly recent smoke in order for them to test positive.”

This is confirmed by the University of Adelaide’s Dr Baldock, who in doing so also recognises the challenges in communicating that message to the public.

“I think great pains have been taken to try and get that message across, but yeah, I’m not sure how well that's got through,” he said.

“You know sometimes people get on, say internet forums, and make that claim and it can take on a life of its own.

“But no you won’t be detected for being positive to cannabis unless you’ve consumed it recently … it’s not going to detect cannabis that was used the day before or anything like that.”

Trent King appealed against his sentence in the Supreme Court, where he was successful in gaining a one-year reduction based on his age and previous good record. However, the judges rejected a separate appeal against his conviction in a decision reaffirmed by the High Court in 2012. At least three-and-a-half years of King’s life would be spent behind bars, the result of what County Court Judge Carolyn Douglas described as “one tragic incident in which two young men’s lives were taken with consequences that devastated two households and would continue to do so”. 

Cannabis users underestimate risk

By JASON WALLS

Australian cannabis users are consistently underestimating the risks involved in driving while under the influence of the drug, according to a research brief published by the National Cannabis Prevention and Information Centre last year.

The brief presents findings from the Australian Institute of Criminology’s drug use monitoring program, which surveyed 857 police detainees in 2008, and found that a third of those who admitted to having used cannabis in the past 12 months also admitted to driving soon after.

The findings back up earlier research indicating that cannabis users tend to lack an awareness of the impact of intoxication on driving, concluding that “those who drive under the influence of cannabis tend to believe that their intoxication has little or no effect on their driving ability”.

NCPIC senior research officer Peter Gates said the data highlighted a need for more resources to be devoted to the issue.

“The problem with a lot of users … is that they are under that incorrect opinion that it’s not affecting their driving, so the research not supporting that [view] just needs to be made more public,” he said.

“Definitely the resources aren't there that need to be.”

Dr Gates nevertheless cautioned against making too many generalisations from the study given its limited focus on detainees.

“That sample of course would be biased to things like risk-taking and driving under the influence in the first place,” he said.

However in a previous study cited in the brief, up to 80 per cent of regular cannabis users reported driving while under the influence at least once in the previous 12 months, with a quarter having done so at least once a week. In that study, only half the participants reported a belief that cannabis use increased their risk of crashing, while 10 per cent believed their risk was decreased.

The Transport Accident Commission’s Elizabeth Waller said the TAC’s Swap campaign, which began in 2009, targeted “the view by some cannabis users that is it okay to drive after using cannabis”.

“The TAC’s message is that if you use drugs, do not drive and put yourself and other road users at risk of serious injury or being killed,” she said.

Cannabis is the most widely used illicit drug in Australia with over 10 per cent of the population admitting to have used it in the previous 12 months in 2010. It is involved in 15 per cent of driver deaths in Victoria, second only to alcohol.