I have long wondered about the facts of this issue when I compare such reports with decades of observing drunks often pranging cars and smokers generally not. I have noticed that laboratory studies usually demonstrate higher risk but population studies don't -- and this report reflects that observation.
I would be interested in the views of others. Comments are open below!
I am automatically suspicious of anything that comes out of NCPIC, which seems to have a mission to demonise cannabis and so-far has a woeful record of amplifying junk science. The new campaign seems much more considered.
However I note a drastic disconnect between the lurid posters they will be flooding schools with, and the conclusion of the research, which begins:
There are numerous methodological limitations in the studies reviewed above that may account for the great variations and inconsistencies in their findings, which detracts from the likelihood of a clear synthesis of results.
The conclusion also speaks about developing new guidelines for cannabis/driving research. I have long thought that a large population study could provide a clearer answer. Take 1,000 or more long-term users (with, say three decades of smoking cannabis) and the same number of people who have never smoked. Then compare their driving and crash records. The study could also look at other factors such as health history, employment, family dynamics, social factors and the like.
Some things I note about the NCPIC report:
• It is not clear whether alcohol has been eliminated as a confounding factor for car accidents in the various population studies.
• Where studies show a percentage of injured drivers testing positive for cannabis, this percentage often seems to be below the percentage of the population which uses cannabis -- so is this statistically significant? There is also a drastic diversity of results from different studies, which makes me wonder about the alcohol factor.
• A common belief among counter-cultures which use cannabis is that the well-known 'paranoid' effects of cannabis cause drivers to be extra-cautious when driving while its other effects make them less aggressive and more relaxed. The old joke about the hippies being pulled over for driving at half the speed limit is legion. This could explain why the laboratory and driving simulator tests show such different results.
• While it is no doubt prudent to advise young people NOT to drive under the influence of cannabis (especially for inexperienced drivers, I would think), this report will be used to justify more drug-testing of drivers who will be penalised at the same levels as for drunk driving when the risk they pose to others is far lower.