Real-world driving behavior, performance, and risk following alcohol and cannabis use in habitual cannabis users

Driving under the influence of alcohol and cannabis remains a significant public safety concern. Simulator studies have documented their impairing effects on driving, yet limited research has explored how these impairments manifest in real-world conditions. This study utilizes a large-scale naturalistic driving dataset to investigate driving behaviors following recent alcohol, cannabis, or combined substance use, aiming to inform effective detection methods and targeted safety interventions.

Naturalistic driving data involving 41 participants from Washington and Virginia were analyzed. Participants drove personal vehicles equipped with data acquisition systems recording location, kinematics, 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). Driving behaviors were analyzed within individuals, comparing driving decisions, roadway exposure, and vehicle control across conditions, supplemented by detailed video annotation for contextual insights.

Alcohol-positive drives were more common during nighttime and weekends, with significantly reduced highway driving exposure. Cannabis-positive trips resembled baselines in timing but demonstrated lower highway mileage, a 5% reduction in speeding, and potential lane-tracking difficulties. Polysubstance trips exhibited combined behaviors from both alcohol and cannabis conditions. Video analyses captured near-crash incidents across cannabis-positive and substance-negative drives.

This study provides the first large-scale naturalistic examinations of alcohol, cannabis, and their combined use during real-world driving. Substance-positive trips demonstrated context-specific behavioral differences, suggesting impairment may manifest in situationally detectable patterns rather than uniform driving deficits. These findings may inform enforcement, clinician counseling, public education, and regionally tailored prevention strategies.