Background and aims
Cannabis and alcohol are frequently detected in fatal and injury motor vehicle crashes. While epidemiological meta‐analyses of cannabis and alcohol have found associations with an ...increase in crash risk, convergent evidence from driving performance measures is insufficiently quantitatively characterized. Our objectives were to quantify the magnitude of the effect of cannabis and alcohol—alone and in combination—on driving performance and behaviour.
Methods
Systematic review and meta‐analysis. We systematically searched Academic Search Complete, CINAHL, Embase, Scopus, Google Scholar, MEDLINE, PsycINFO, SPORTDiscus and TRID. Of the 616 studies that underwent full‐text review, this meta‐analysis represents 57 studies and 1725 participants. We extracted data for hazard response time, lateral position variability, lane deviations or excursions, time out of lane, driving speed, driving speed variability, speed violations, time speeding, headway, headway variability and crashes from experimental driving studies (i.e. driving simulator, closed‐course, on‐road) involving cannabis and/or alcohol administration. We reported meta‐analyses of effect sizes using Hedges’ g and r.
Results
Cannabis alone was associated with impaired lateral control e.g. g = 0.331, 95% confidence interval (CI) = 0.212–0.451 for lateral position variability; g = 0.198, 95% CI = 0.001–0.395 for lane excursions) and decreased driving speed (g = –0.176, 95% CI = –0.298 to –0.053. The combination of cannabis and alcohol was associated with greater driving performance decrements than either drug in isolation e.g. g = 0.480, 95% CI = 0.096–0.865 for lateral position variability (combination versus alcohol); g = 0.525, 95% CI = 0.049–1.002 for time out of lane (versus alcohol); g = 0.336, 95% CI = 0.036–0.636 for lateral position variability (combination versus cannabis; g = 0.475, 95% CI = 0.002–0.949 for time out of lane (combination versus cannabis). Subgroup analyses indicated that the effects of cannabis on driving performance measures were similar to low blood alcohol concentrations. A scarcity of data and study heterogeneity limited the interpretation of some measures.
Conclusions
This meta‐analysis indicates that cannabis, like alcohol, impairs driving, and the combination of the two drugs is more detrimental to driving performance than either in isolation.
•Youth aged 16–24 years have the highest prevalence rates of cannabis use.•A scoping review explored predictors of driving under the influence of cannabis (DUIC).•Nineteen primary studies, which met ...inclusion criteria, were identified.•A variety of demographic and consumptive predictors of DUIC in young drivers were identified.•Gaps in research and future directions are discussed.
Recreational and medical legalization of cannabis or marijuana use in countries and states continues to increase. Young adults aged 16–24 years have the highest prevalence rates of cannabis use. Young driver cannabis use is an incompletely understood traffic safety issue.
The purposes of this scoping review were to characterize the predictors of driving under the influence of cannabis (DUIC) among healthy young drivers and to identify research gaps.
A self-reported measure of DUIC and a correlation (r, odds ratio, risk ratio) to demographic or behavioral variables such as age, gender and frequency of use was required for inclusion
APA PsycInfo, SPORTDiscus, Academic Search Complete, Google Scholar, MEDLINE Complete, Scopus, Embase, ERIC, TRID and POPLINE databases were searched using an a priori protocol.
The PRISMA-ScR methods and checklist were used to conduct the scoping review. After the removal of duplicates, abstract screening (N = 999), and full-text review (N = 173), 19 primary studies met inclusion criteria. Predictors were coded and mapped into four primary thematic categories: social, individual, driving and substance use.
Of the included studies, a total of 52,197 respondents were surveyed in-person or online and 51.8 percent were males. The predominant predictors of DUIC included being a male, high school senior, with lower grades, having a younger ‘age of first cannabis use’, a higher frequency of consumption, a reduced perception of danger, repeatedly binge drinking, a history of driving under the influence of alcohol and living with fewer parents.
Identified research gaps include methods used to study young drivers, cannabis edibles, chronic user tolerance, driver adaptation, passengers of drivers who consumed cannabis, combined use with other legal and illicit drugs, and combined smartphone and cannabis use.
The results of this scoping review can be used to develop and target general and specific predictors of DUIC in novice, teen and young drivers. Additional research designs will be required to gain a more complete evidence-based understanding of the effects of cannabis on young drivers.
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