Many posts ago, I observed that while bicycling home at night, I occasionally chanced upon the smell of marijuana drifting out of cars that had stopped next to me at red lights.
A few readers said they thought that, from my tone, I disapproved.
I guess I do. Guy on bicycle riding in traffic with operators of big motor vehicles who might be stoned. Hmmm.
But is there really reason for concern? Where’s the proof that smoking marijuana while driving causes impairment?
A story at nytimes.com reports that there have been several studies, but they have not been conclusive. There’s a great deal of evidence showing that drinking alcohol and then driving is very dangerous. But the stack of evidence arguing against marijuana use and driving isn’t as substantial.
In fact, in your typical sobriety test, involving things like standing on one foot for 30 seconds and walking in a heel-toe straight line, people who had just smoked marijuana often pass.
Still, studies have found that there’s definitely reduced driving ability when a driver smokes marijuana immediately before or while driving, though being stoned tends to be less dangerous than being drunk. A consensus among experts is that someone with measurable THC, marijuana's active ingredient, in the bloodstream is twice as likely to have an accident, versus someone who is sober.
Here’s a link to the New York Times story, by Maggie Koerth-Baker.
And a link to one of the studies.
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A 2010 study in British Columbia sought to gauge the amount of alcohol and drug use among motorists. Researchers asked for voluntary oral fluid samples from motorists who were stopped by police in Saanich, Vancouver, Kelowna, Abbotsford and Prince George. Those oral fluid samples were taken using a swab designed for that purpose. Of 2,840 drivers stopped, 71% provided an oral fluid sample. The least willing were in Vancouver, most willing in Prince George.
Lab analysis of the oral fluid samples found 9.1% were positive for drugs. Those drug included:
• 63.8% cannabis
• 31.8% cocaine
• 11.1% opiates
• 4.8% amphetamine
• 4.2% methamphetamine
• 2.4% benzodiazepines
After weighting the data for traffic volume, the study reported that out of 494 oral fluid samples taken in Saanich, 35 tested positive for a drug — 7.1%. For all five communities, 7.2% tested positive.
The study’s authors cautioned that their results were based on voluntary participation. People were told that the results would remain confidential. Despite that, people who had taken drugs were probably less likely to volunteer an oral fluid sample, the authors said.
Read the full study here (it’s a slow-loading PDF).
The study was done for the Canadian Centre on Substance Abuse, and partially financed by the B.C. government and the Insurance Corporation of B.C.
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There are no accurate tests for finding the level of intoxication in a marijuana user, says an article by Mike Adams at hightimes.com.
It quotes Dana Larsen of Sensible BC, a group that wants to decriminalize simple possession of marijuana in British Columbia. This is an excerpt from that article:
“There’s quite a bit of difference with a first-time, non-experienced marijuana user and somebody who’s using it every day for medical purposes or otherwise, in terms of impairment and how it affects you,” said Dana Larsen of Sensible BC.
Larsen says that unfortunately, the issue is touchy and difficult to remedy because no one wants to come across as if they are promoting impaired driving. However, he contends that in the case of medical marijuana, patients may actually drive better when they are high because they are less likely to be distracted by the symptoms of their conditions.
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Some more articles to add to the uncertainty:
The confusing science of stoned driving, by David Bienenstock
He points to a story in the Denver Post:
Report shows fewer traffic fatalities after states pass medical-pot laws. A reason cited by a researcher quoted in the article: young people are spending less time drinking alcohol and more time smoking marijuana.
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