Study to explore link between marijuana use and car crashes next, permission, collected, question, explore

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Study to explore link between marijuana use and car crashes


VANCOUVER -- Injured drivers taken to B.C. hospitals over the next five years will help answer the question: Do those who are high on marijuana cause more crashes than sober drivers?

In the marijuana-impairment study — the first of its kind in Canada — injured drivers will not be asked permission before their blood is collected. Since the data is collected anonymously and not used to pursue legal charges, researchers don’t have to seek approval from drivers to analyze their blood under the ethics-approved terms of the study.

Blood is drawn for treatment of any injuries and the excess amount is then analysed. The sample is assigned a code that is not shared with police, and the resulting data is then linked to police accident reports to eventually show researchers if cannabis contributed to the accident.

A recent random sampling of B.C. drivers showed that 10 per cent were impaired by alcohol and 7.2 per cent by drugs, usually marijuana or cocaine. Concentrations of THC, the active ingredient in cannabis, are what will be measured in the study, which is led by Dr. Jeffrey Brubacher, an emergency doctor at Vancouver General Hospital.

After alcohol, cannabis is the most widely used intoxicating substance in the world; in the aforementioned B.C. survey it accounted for about two-thirds of the drugs detected after police roadside stops (followed by cocaine). Many marijuana users think it’s less hazardous because cannabis tends to make people drive more slowly and less aggressively than, say, drivers who are drunk on alcohol, according to studies.

But, at the same time, drivers high on marijuana have a harder time staying within lanes and their reflexes are slower, which means they are more likely to crash into obstacles that suddenly appear. On the other hand, “cannabis users tend to overestimate their impairment whereas people who used alcohol underestimate theirs,” Brubacher stated in an explanation of his study in the B.C. Medical Journal.

Brubacher said data on the first 100 injured drivers have already been collected for the study, which aims to include information on 3,000 crash-involved drivers at five B.C. hospitals.

THC levels in blood — which are measurable no matter how the cannabis is consumed (smoked, sprayed, drunk, or eaten) — yield a blood THC concentration considered more accurate than THC metabolites in urine. Brubacher said urine metabolites remain active for days after cannabis exposure, even though impairment typically lasts less than four hours.

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“Our primary objective is to determine whether injured drivers who used cannabis before a motor vehicle accident are more likely to have caused the crash than those who did not,” said Brubacher, adding that the number of crashes caused by impaired drivers will be compared to a control group of drivers who were found to be not culpable.

The ultimate goal of the $1-million study, funded by the federal Canadian Institutes of Health Research, is to help traffic-safety experts develop safer driving policies. It is possible, for example, that the study might show whether there should be a legal cutoff level for THC blood concentration, just as there is for alcohol. The study results should also help inform the debate around whether marijuana possession should be decriminalized.

When it comes to drug-impaired drivers, current practice is for police to do a roadside sobriety test if they have suspicions. If the driver fails the initial observational tests (walking a straight line, etc.) then the driver must accompany the officer to a police station for further examination by a specially trained Drug Recognition Expert. Drivers may be ordered to submit blood, saliva or urine samples, or face a fine for refusing to comply.

While there have been some surveys showing that drivers impaired by cannabis were nearly twice as likely to crash, Brubacher and his co-investigators are using a similar “culpability” study design as was used in studies in Australia and France, linking data from injured drivers to police reports to show who caused the accident and their level of impairment.

Those studies had a few drawbacks, however, including a cumbersome process in which the drawing of blood was delayed about three hours from the time of the crash.

“We anticipate that our data will provide a more accurate reflection of true THC levels at the time of crash,” Brubacher said, noting that in a pilot project, the average time from crash to blood draw was 53 minutes.

RCMP Supt. Norm Gaumont said he’s pleased the study is being conducted because compared to the evidence about the dangers of drunk driving, there is little research on the effects of drug-impaired driving. Gaumont, who heads traffic services in B.C., said there is urgency to get the type of data in the study because of a steady increase in the number of deaths caused by drug-impaired drivers. At last count, B.C. coroners showed there were 62 deaths (out of 374 in 2008) attributable to drug-impaired drivers.

“Drug impairment is becoming a bigger and bigger problem. We’ve done a good job educating people about drunk driving, but [offered] very little on drugs. So certainly this study will be a benefit,” Gaumont said. He added that B.C. law-enforcement authorities are monitoring studies in Europe and Australia, where police are experimenting with roadside saliva tests that can yield instant information about what drugs drivers have used, and their level of impairment.

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In the marijuana-impairment study — the first of its kind in Canada — injured drivers will not be asked permission before their blood is collected

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