Drivers who perceived more stimulation from cannabis showed less negative impact on driving, while those who felt more "stoned" or "high" showed greater impairment.
Driving safety researchers, cannabis users concerned about impairment, impairment testing developers
Stimulation effects were associated with less driving impairment
What the researchers found
Subjective cannabis effects predicted changes in driver inputs (steering frequency, reversal rate), while actual driving performance measures like lane weaving were better predicted by dosing condition. Drivers reporting more stimulation showed better performance, while those feeling more stoned showed worse performance.
Why it matters
If different subjective experiences from cannabis predict different levels of driving impairment, this could have implications for how we think about cannabis strain effects and impairment testing.
The numbers in context
10 subjects; driving measured ~2 hours after inhalation; 6.9% THC vs placebo; subjective measures collected at peak and before driving
How the study worked
Analysis of 10 subjects in a driving simulator study approximately two hours after cannabis inhalation (6.9% THC vs placebo), examining relationships between subjective effects and driving performance using visual analog scales and simulator metrics.
What this study cannot tell us
Very small sample (10 subjects), single THC potency tested, simulated rather than real-world driving, subjective self-reports may not be reliable measures of actual impairment.
How to read the evidence
Very small randomized study with only 10 participants using simulated driving
When this study was published
Published in 2021. Research on how subjective cannabis effects relate to driving impairment is in early stages.
The bigger picture
This suggests that different cannabis strains producing different subjective experiences could have varying impacts on driving safety, complicating blanket impairment laws.
Questions still open
- Do indica vs sativa strains reliably produce different driving impairment levels? Could self-reported subjective effects be used as a practical impairment screening tool?
Common questions
Does how cannabis makes you feel predict driving impairment?
Can cannabis users tell if they are too impaired to drive?
Read the original research
Perceived effects of cannabis and changes in driving performance under the influence of cannabis.
Traffic injury prevention, 22(sup1), S8-S13
Citation
Burt, Thomas S; Brown, Timothy L; Schmitt, Rose; McGehee, Daniel; Milavetz, Gary; Gaffney, Gary R; Berka, Chris. (2021). Perceived effects of cannabis and changes in driving performance under the influence of cannabis.. Traffic injury prevention, 22(sup1), S8-S13. https://doi.org/10.1080/15389588.2021.1933459