Researchers at the Colorado School of Public Health (CSPH) are investigating the effects of cannabis use on driving performance. Utilizing a driving simulator that mimics real-life scenarios, they assess how participants drive before and after consuming cannabis products, specifically those containing tetrahydrocannabinol (THC), the main psychoactive component that influences perception, coordination, and reaction times.
Ashley Brooks-Russell, PhD, MPH, an associate professor at CSPH, highlights that approximately one in five Coloradans reported cannabis use in the past month, with nearly half of those individuals using it daily. This raises questions about the impact of cannabis on driving, especially among older adults.
CSPH Study Focuses on Older Adults
To explore these effects, CSPH is currently recruiting healthy adults aged 65 to 89 who drive and have consumed cannabis at least once a month over the past two months. Data from 2024 reveals concerning trends regarding cannabis use among drivers in Colorado:
- 16.3% of Colorado drivers who used cannabis in the past 30 days reported driving within two to three hours of use.
- 45 fatalities occurred due to impaired drivers under the influence of cannabis.
- The rate of combined drug and alcohol fatalities rose from 26% to 32% since 2017.
Brooks-Russell emphasizes the need for caution, stating, “Given that a substantial part of the population is using cannabis, we should have concerns about road safety.” Notably, cannabis affects driving differently than alcohol, as cannabis users do not typically exhibit aggressive driving behavior.
Impact of Cannabis on Driving Performance
Key findings from CSPH’s research indicate significant variations in driving performance attributed to cannabis use:
- Cannabis use was linked to changes in driving performance, particularly with lane-control metrics such as weaving and lane departures.
- Inhaled cannabis produced less consistent changes in driving behavior compared to edibles.
- Edible cannabis resulted in notable impairments, including reduced speeds and increased lane variability.
- Occasional cannabis use led to greater impairment than daily use, indicating that tolerance affects driving performance.
- Differences in driving behaviors became more obvious at higher speeds, where maintaining lane position proves more difficult.
Understanding Different Forms of Cannabis
Brooks-Russell’s team has researched various forms of cannabis, focusing on inhaled products and edibles. Inhaled cannabis, including smoked flower and vape oils, produces immediate effects, while edibles are metabolized slowly. “Edibles are processed through the digestive system, so the onset is slower, and the effects last longer,” Brooks-Russell noted. This delay in effects can lead individuals to consume more than intended or drive before the impairment manifests, with some edibles causing impairment for several hours.
Researchers examined three groups in their studies: a control group with no cannabis use in the past 30 days, an occasional use group, and a daily use group. Participants self-administered their usual cannabis dosages to reflect real-world usage accurately.
Driving Simulator Research
Participants operated a driving simulator designed to replicate the experience of driving a real vehicle, complete with a steering wheel, pedals, and a dashboard. The simulator features a large touchscreen, allowing for distractions like music and text messages. Each participant experienced a sober baseline drive before consuming cannabis and completing two additional drives.
The focus was on key indicators of risky driving behaviors, such as lane position and lane departures, which serve as reliable proxies for crash risk. The study found that drivers consuming inhaled cannabis exhibited minimal performance changes, with occasional users showing some increase in lane departures. In contrast, those using edibles displayed reduced speeds and increased lane weaving.
Research on Cannabis and Aging Drivers
Professor Carolyn DiGuiseppi, PhD, MD, MPH, is also examining how cannabis impacts the driving behaviors of older adults, particularly those aged 65 and above. This research focuses on individuals without dementia but may have mild cognitive decline associated with aging. Understanding how cannabis affects this demographic is vital, especially as their usage rates increase.
As cannabis use becomes more widely accepted, clear guidelines for impairment are lacking, with no standardized roadside tests available akin to those for alcohol. Both Brooks-Russell and DiGuiseppi stress the importance of safe driving practices, urging individuals to refrain from driving if they feel impaired.