A new way to study how cannabis use impacts safe driving

OG article by Gwen Sheldon

February 19, 2026

Virginia Tech Transportation Institute (VTTI) completed a two-year naturalistic driving study (2021–2023) analyzing cannabis's effects on road safety, gathering 105,000 miles across 14,700 trips from drivers aged 21–70 in Washington and Virginia. Sponsored by the National Surface Transportation Safety Center for Excellence, it used driver-facing cameras, sensors, journals (10,081 entries), and oral swabs for substance verification. Data covered 9,000 cannabis-involved miles, 1,000 with alcohol, 400 polysubstance, and baselines substance-free. Lead researcher Kaitlyn Bedwell highlighted cannabis impairment's complexity—no equivalent to blood alcohol content exists, as THC lingers up to 30 days and varies by metabolism and potency. The study tracked real-world patterns, like cannabis trips peaking at lunch, evenings, and Fridays, with some drivers choosing safer rural routes as compensation. Published in the 2025 report “Naturalistic Driving Study on Cannabis Use in Washington and Virginia,” findings offer a replicable, holistic method combining qualitative/quantitative data and individual baselines. As 40 states legalize marijuana, this addresses key research gaps to inform impaired-driving policies.