High On Pot

"[The effects of cannabis are cognitively based] They're in your head. And you can see effects on things like concentration. When you're driving you have to concentrate on a million different things at once, but you can't switch your attention as easily [high on pot]."
"[When governments introduced the 0.08 blood limit for alcohol] we probably made a mistake. What we did essentially was tell people it was OK to drive after drinking [as long as the limit wasn't exceeded. Decades later] we're pondering the same question, and whether we set a limit, any limit, whatever it might be, for cannabis, we're still saying to people, 'It's still OK to go out and smoke cannabis and drive. Just don't get over that limit'."
"What we need to do is create a culture where driving after smoking cannabis is just not OK."
Doug Beirness, vice-chairman, Canadian Society of Forensic Science

Justin Tang/The Canadian Press    A woman takes part in the annual marijuana rally on Parliament Hill on April 20, 2016.

"There is no concentration -- no matter how high or low -- that we can use to reliably predict impairment in a driver."
Jake Nelson, director of traffic safety advocacy and research American Automobile Association

Postmedia News  Twenty per cent of Canadians who drive while high say nothing will make them stop.

Now that Canada is getting set to legalize marijuana possession and use, the question arises how to formally ensure through appropriate laws that a substance whose use will temporarily alter a user's capacity to think and react normally, doesn't constitute a potential menace on the highway? Just as alcohol consumption and driving don't mix, neither will the intake of recreational drugs and driving. Society knows well enough that alcohol and driving cause carnage on the road. Depending on people to be sensible and sensitive to the safety and security of other people is quite often a lost cause.

But now, in Canada a scientific advisory committee is in the process of preliminary work toward advising the government on how to arrive at what will be considered a 'safe' range of THC in the bloodstream, for driving purposes. THC is the major psychoactive component of marijuana. International literature is being studied by the advisory committee to try to ascertain what a consensus on appropriate blood-level limits might be.

Several states in the U.S. have set THC limits for safe driving. Those limits range from one nanogram of THC per millilitre of blood, to five. In other states the presence of any level of THC is forbidden. "What a lot of people want is a number for Canada. It's a legal shortcut. It means that the prosecutor does not have to prove that the person's ability to operate a vehicle is impaired. It's a given -- if you're over this number, it's a given you're impaired", pointed out Doug Beirness who is also a senior research associate for the Canadian Centre on Substance Abuse.

His concern is that in setting a legal THC limit a message would be conveyed to drug users that it is safe, within circumscribed limits, to drive while high. He points out that the effects of liquor are "profoundly physical", resulting in slurred speech, imbalance, warped motor co-ordination for example, while the effects of cannabis use are centred in the head; cognitively based. In a State Farm survey of 3,000 Canadians of driving age across Canada, almost nine of ten respondents claimed never to have driven under the influence of marijuana.

On the other hand, 44 percent of people who do drive while high feel they are capable of driving safely. According to Jake Nelson of the AAA, other research has indicated that many motorists believe marijuana "isn't that unsafe". And also go so far as to believe that the use of marijuana results in better driving.  The American Automobile Association sponsored a study to compare drivers testing positive for THC to drug-free 'controls'. Researchers studied how well THC concentrations correlated, or not, with scores on roadside sobriety tests by trained drug recognition experts.

Darren Calabrese/National Post     Police in Canada have been able to demand roadside sobriety tests on suspected drugged-drivers since 2008.

Weed-positive drivers, it turns out, were likelier to exhibit physical signs of being high, and they performed less well on -walk-and-turn' tests and one-leg stand tests. They also experienced greater misses on the finger-to-nose-test. The conclusion was reached nonetheless that "neither the walk-and-turn, nor one-leg stand tests demonstrated increasing rates of error as a function of THC concentration", according to the report. The significant difference was the finger-to-nose test where drivers with  higher THC concentrations found it more difficult to reach their noses.

Researchers found as well that minimal differences existed between people with THC levels above or below five nanograms. Just as some people 'hold their liquor well', and become less impaired than others who drink less but are more physically affected, the same can be said for pot users. Using a figure where it is believed those who have indulged in cannabis can safely drive is an arbitrary figure since people are affected differently. Which brings us right back to Mr. Beirness's conclusion that "What we need to do is create a culture where driving after smoking cannabis is just not OK".

And good luck on that one.