A study is to take place in Canada by the University of Victoria’s Centre for Addiction Research B.C (CARBC) and will investigate whether there is firstly a link between marijuana and car crashes but secondly what the risk of impairment is whilst driving at various levels of smoking pot.
This may be the first study in Canada but similar studies have been done by governments and scholars around the world. Many of which have found the effects of marijuana on driving as minimal. For instance the U.S department for transport published a report (Marijuana and Actual Driving Performance) where it states that the active ingredient in marijuana (THC) has a "relatively small" risk of causing dangerous driving. The report goes on to say that people under the influence of cannabis "retain insight in to their performance" and thus compensate such as driving slower. The study also notes that compared to medicinal drugs and alcohol marijuana’s effects are not exceptional.
Studies which have found a link between marijuana and crashes are also sometimes inaccurate due to the fact that they don’t necessarily take into account other variables such as alcohol. For instance as Ramaekers, Robbe and O’Hanlon openly admit previous studies have had a problem in that 50-90 % of those who crashed who had marijuana in their system also had alcohol in their system. This means the crash cannot possibly be blamed solely on the use of marijuana and neither can a study be completely legitimate if there are other factors at play, such as the use of other substances.
If anything studies which have been done have shown that is it more likely the fault of alcohol. A study by Institute for Human Psychopharmacology (Marijuana’s Effect on Actual Driving Performance) mentioned that their study supported the general perception that "drivers become overconfident after drinking alcohol" and "become more cautious and self-critical after consuming low doses of THC". Also there was a report by the Department for the environment, transport and regions (the influence of cannabis on driving) in the UK admitting that when it came to driving, alcohol was a much larger risk than marijuana.
Other studies such as the one conducted in a controlled environment by Sutton (The effects of alcohol, marijuana and their combination of driving ability) have show that marijuana alone does not impair "driving performance" , but the combination of even a low dose of alcohol and marijuana has a dangerous effect on driving. This study combined with the studies in the above paragraph surely show that the more dangerous substance when driving is not marijuana but instead is alcohol.
The study in Canada must therefore make sure that the results are based on incidents where the only substance found in each crash victim’s body is marijuana. If there is alcohol in their system then there is more likelihood that it is the alcohol that caused the crash and not the marijuana. Especially since studies have shown that marijuana actually makes people drive slower compared to alcohol where studies have shown that it causes reckless driving.
So far the only available information about how this study is going to be run is a media release by the University of Victoria. Where they state that they will test blood samples of those involved in car crashes for THC. The media statement continues by saying that "[t]his will indicate to researchers whether marijuana use contributed to the accident". There is no mention about checking for small doses of alcohol (which the Sutton study shows can in conjunction with marijuana cause dangerous driving) which could mean that this study due to the potential lack of checks for other substances and the lack of a controlled environment produces results which are not accurate or representative of the actual risk between marijuana and driving.
Though blood tests are a good indicator of impairment from marijuana and do tell if a person has recently used marijuana they are not completely accurate in determining how much of an effect it will have on the subject. Chronic users often develop tolerance to THC and therefore drive safely even with THC in their blood. In other cases THC can actually help someone to drive safely. One case mentioned by Strohbeck-Kühner involved someone with severe attention deficit disorder who failed a driving test when not on marijuana yet when he had 71 NG/ML of THC in his blood the subject performed well on a driving test. Therefore it is not safe to assume that just because there is THC within the subject’s blood that it was the cause of the crash.
The accuracy of this study has to be questioned even at this early stage due to the possible problems which have been highlighted above. It may be more accurate than some other studies which have used urine instead of blood but there are still fundamental problems with this study. The Victoria News says that the collisions caused by people under the influence of marijuana is hazy. That is questionable considering there have been countless studies which have been done by governments and researchers proving that the effects are relatively small compared to the dangers of drinking and driving.