There is growing concern about driving under the influence of cannabis (DUIC), especially as more states consider changing laws regarding cannabis possession and use. A key question regarding the legalization of cannabis for recreational or medical purposes is its potential impact on public health issues. Specifically, there is considerable uncertainty and debate about the impact of cannabis and its legalization on traffic safety. Among the general population, one study indicated that 36 percent of the population perceive no risk associated with DUIC. Ten percent even perceive that DUIC reduces crash risk.
This uncertainty and debate can be attributed to the complex effects of cannabis on traffic safety compared to alcohol, which is a very different form of drug with a long history of research and attention in traffic safety. Information that might increase understanding and resolve debate about the effects of cannabis on traffic safety is often published in academic journals. However, this information may not be accessible to lay audiences and traffic safety practitioners and policymakers. This inaccessibility can hinder attempts for traffic safety practitioners and policymakers to decide on appropriate polices and implement effective strategies to mitigate risk.
Research indicates that DUIC increases the risk of the driver being fatally injured in a motor vehicle crash, especially when combined with alcohol. THC-positive drivers appear more likely responsible for these crashes.
The mechanism for increased crash risk appears to begin neural changes impair cognitive functions necessary for driving, especially attention. The impairment of core cognitive functions translates to impairment of driver behaviors, most notably those not requiring conscious control. The absence of conscious control for these behaviors means that it is not possible for drivers to compensate for their impairment.
Decriminalization of cannabis increases access. It is logical to expect an increase in DUIC and motor vehicle crashes, especially those related to the behavior of impaired drivers. It is difficult to isolate the causal effect of cannibis laws on traffic safety metrics. There have been too few analyses of the effect of such laws on traffic safety using only a few states (CO, OR, WA) and relatively short post-legislation periods. Thus, there is insufficient evidence to make any conclusions about the effects of legalization of cannabis on traffic safely. Laws regarding DUIC are a public health issue, thus they need to reflect the risk imposed by the drug across the entire driving population, rather than reflect the unique circumstances of a small minority of individuals.
Prepared by Nicholas Ward, Ph.D.; Jay Otto, M.S.; Kari Finley, Ph.D.; Center for Health and Safety Culture, Western Transportation Institute, Montana State University, Bozeman.
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