Blacksburg, VA: Drivers increase their speed following the use of alcohol while they reduce their speed following the use of cannabis, according to an assessment of real-world driving performance published in the journal Accident, Analysis & Prevention.
Researchers at Virginia Tech’s Transportation Institute and the Transportation Research Center assessed real-world driving performance in a cohort of 41 participants. Participants drove personal vehicles equipped with data acquisition systems recording location, kinematics (vehicle acceleration, motion, and velocity), and video. Substance use was assessed through pre-drive self-reported surveys and periodic breathalyzer and saliva tests, allowing trips to be categorized as substance-negative, alcohol-only, cannabis-only, or polysubstance (alcohol and cannabis).
Consistent with driving simulator data, participants who consumed cannabis engaged in compensatory driving behavior. Researchers reported: “Alcohol-involved trips showed increased proportions of speeding on primary and secondary roads, suggesting impaired judgment or compromised longitudinal vehicle control. In contrast, cannabis-positive trips had speeding proportions closely aligned with baseline conditions, likely indicating habituation or compensatory driving behaviors.”
The study’s authors concluded: “This study marks a significant advancement in impaired driving research by conducting the first large-scale, naturalistic analyses of cannabis, alcohol, and their combined use in real-world driving contexts. … Overall, this study contributes valuable real-world evidence to a field that has long relied heavily on experimental paradigms. It offers early estimates of how cannabis and polysubstance use may affect driving behavior and begins to bridge the gap between tightly controlled experimental studies and the complexity of real-world behavior. As cannabis legalization continues to expand and polysubstance use becomes increasingly common, efforts like this will be essential in shaping more informed, evidence-based traffic safety policies and public health strategies.”
Full text of the study, “Real-world driving behavior, performance, and risk following alcohol and cannabis use in habitual cannabis users,” appears in Accident, Analysis & Prevention. Additional information on cannabis and driving is available from the NORML Fact Sheet, ‘Marijuana and Psychomotor Performance.’