|
Citation
|
Ward NJ, Otto J, Finley K. Montana Department of Transportation (SPR)- Research Programs. Bozeman, MT USA: Center for Health and Safety Culture, Montana State University, 2019. |
|
Abstract
|
There is growing concern about driving under the influence of cannabis (DUIC), especially as more states consider changing laws to legalize cannabis. A key question regarding the legalization of cannabis for recreational or medical purposes is its potential impact on public health issues such as traffic safety. To address the needs of traffic safety practitioners and policymakers, this synthesis report seeks to summarize key information about the role of cannabis in traffic safety in order to inform policy regarding cannabis legalization and traffic safety.
Main conclusions include:
• Cannabis is a plant-based drug that is typically smoked or ingested.
• Cannabis is the most commonly used illicit drug in the U.S.
• The primary psychoactive compound of cannabis is delta-9-tetrahydrocannabinol (THC).
• THC is transported by the circulatory system to the brain where it alters neural activity and brain functions.
• Changes in neural activity and brain functions can impair core cognitive functions such as attention.
• Cognitive impairment results in impaired driving behaviors.
• Impaired driving behaviors increase driver responsibility for motor vehicle crashes.
• THC-positive drivers are twice as likely to be killed in a motor vehicle crash.
• The fatal crash risk is much higher when THC is combined with alcohol.
Currently, there is some evidence that the legalization of recreational cannabis increases crashes. However, because it has been only recently that relatively few states have adopted this legislation, the amount of evidence is insufficient for a definitive conclusion. Thus, there is a need for more research to examine the effect of cannabis legalization on traffic safety. Such research will require longer post-legalization periods and more states that have enacted these legislative changes.
There is much debate and conflicting evidence about the effect of cannabis on fatal crash risk. However, an examination of international literature reviews and meta-analyses suggests that the preponderance of evidence indicates that driving under the influence of cannabis (DUIC) increases the risk of the driver being fatally injured in a motor vehicle crash, especially when combined with alcohol. Indeed, THC-positive drivers also appear more likely to be responsible for these crashes, probably because of insufficient attention or excessive speeding.
The mechanism for this increased crash risk appears to begin with the effect of THC on brain activity and functioning. These neural changes then impair cognitive functions that are 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 on conscious control for these behaviors means that it is not possible for drivers to compensate for their impairment.
To the extent that decriminalization of cannabis increases access within a population – including drivers – it is logical to expect an increase in DUIC and associated motor vehicle crashes, especially those related to the behavior of impaired drivers. However, it is pragmatically difficult to isolate the causal effect of cannabis laws on traffic safety metrics. Moreover, there have been too few rigorous 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, it is insufficient evidence to make any conclusions about the legalization of cannabis on traffic safety.
Such conclusions may be disputed by individuals who believe they drive safely after using cannabis. However, evidence that tolerance to the acute effects of cannabis can be developed is inconclusive. Even those cannabis users professing they can compensate for the acute effects of cannabis are truly unable to compensate completely for their impairment. Regardless, laws regarding DUIC are a public health issue – and as such – 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.
Key Words: Cannabis impaired driving; DUID; Ethanol impaired driving, Impaired Drivers, Drugged Drivers, Drugs, Marijuana, Traffic Safety, Crashes, Policy, Safety Culture, Safety, Risk Taking, Alertness, Attention Lapses, Attention, Fatalities, Social Factors, Social Impacts, and Externalities |