Countermeasures and Strategies to Address Cannabis-Impaired Driving; A Multi-State Survey Study
October 23, 2025
At the October CMCR Investigators’ Meeting, Dr. Linda Hill, Distinguished Professor at UC San Diego and Director of the Transportation Research and Education for Driving Safety (TREDS) program, and Sarah Hacker, Research Program Manager and Data Analyst at the Herbert Wertheim School of Public Health, presented findings from a multi-state study conducted by UC San Diego’s TREDS team in collaboration with the AAA Foundation for Traffic Safety to understand how to reach drivers who use cannabis and still get behind the wheel.
The project unfolded in three parts: interviews with national subject-matter experts; a broad, anonymous survey of 2,000 adults from eight states spanning fully legal, medicinal-only, and illegal cannabis laws; and a second survey (n ≈ 846) testing specific public-safety messages among medium- to ultra-high-risk same-day users.
Key patterns emerged. First, legality didn’t neatly predict use: self-reported cannabis prevalence was similar across legal and illegal states. Risky driving behavior was common—about half of users reported driving within an hour of use. Many believed cannabis did not worsen their driving, and a sizeable minority believed it improved it. Knowledge gaps were striking: in medicinal-only and illegal states, many participants misunderstood their state’s legal status and driving restrictions, and few cited fear of being stopped by police as influencing wait times before driving.
Message testing offered practical direction. Three messages consistently resonated: “Driving high is driving impaired,” “If you feel different, you drive different,” and “THC slows reaction time.” Pairing messages with images emphasizing consequences and community safety—along with clear alternatives such as rideshares—enhanced impact. Trust mattered: safe-driving advocates, healthcare providers, and science organizations were more credible than influencers or polarizing law-enforcement imagery. The toughest audience was the ultra-high-risk group (often younger, male, frequent users), who tended to be less trusting and more likely to feel “immune” to impairment; however, medium-risk users showed meaningful openness to changing behavior.
Bottom line: Broad, evidence-based campaigns already in use work, especially when they highlight impairment, promote alternatives to driving, and come from trusted messengers. To reduce cannabis-related crashes, prioritize targeted education in lower-knowledge states and tailor outreach to move medium-risk drivers toward safer choices.
Dr. Linda L Hill, MD, MPH
Dr. Linda L Hill, MD, MPH, is a Distinguished Professor and Founding Faculty of the Herbert Wertheim School of Public Health, where she is also Associate Dean. Dr. Hill obtained her MD from the University of Ottawa, in Ottawa, Canada in 1978 and completed a transitional internship at McGill University in 1979. She completed her residency in Preventive Medicine from the University of California San Diego (UCSD)/San Diego State University (SDSU) General Preventive Medicine Residency in 1985. She is a Fellow of the American College of Preventive Medicine. She was the founding Medical Director of the Exercise and Physical Activity Resource Center at UCSD at Qualcomm Institute. She is Faculty and immediate past Program Director of the UCSD/SDSU General Preventive Medicine Residency since 1989. San Diego Family Care, a Federal 330 Community Health Center, is the site of her clinical activities, as Medical Director 1980 to 2001, and Senior Staff Physician since 2001. She is the Director of the UCSD Training, Research and Education for Driving Safety (treds.ucsd.edu) and Co-Director of the UCSD Center for Human and Urban Mobility. She is the Executive Director of the Asylum-Seeker Shelter Health Assessment Program. Dr. Hill is engaged in prevention research and teaching, with current and past support from the NIH, the California Office of Traffic Safety, Robert Wood Johnson, American Cancer Society, Health Services Resource Administration, Caltrans, Federal Motor Carriers Service Association, and AAA Foundation for Traffic Safety, Caltrans, and the Bureau of Cannabis Control and is the author of 110+ peer reviewed papers, 4 book chapters, and 140+ abstracts. Her hobbies include classical piano and ocean sports.
Sarah Hacker
Sarah Hacker is currently a Research Program Manager and Data Analyst at the Herbert Wertheim School of Public Health at UC San Diego. Sarah currently works with Dr. Linda Hill and TREDS (Transportation Research and Education for Driving Safety) on a variety of transportation safety projects. Her educational background is in psychology (cognition and neuroscience) and statistics, and she has used this to study driving behavior in a variety of populations. She has produced several grants, technical reports, and presentations on impaired driving, including cannabis-impaired driving.