A study of 31 young occasional cannabis users found that while cannabis significantly impaired visual function, drivers did not self-regulate their speed to compensate.
Traffic safety researchers, cannabis users who drive, policymakers.
Cannabis impaired vision significantly but drivers did not slow down
What the researchers found
After smoking cannabis, visual acuity and contrast sensitivity were significantly impaired. However, drivers did not reduce speed. Road curves did prompt self-regulation. Males drove faster than females. Those with greater contrast sensitivity impairment showed some lateral control changes.
Why it matters
This challenges the argument that cannabis users "know they are impaired" and compensate by driving more cautiously.
The numbers in context
31 young occasional cannabis users. Significant visual impairment. No speed self-regulation. Males drove faster. Contrast sensitivity linked to lateral control.
How the study worked
Within-subjects design with 31 young occasional cannabis users assessed at baseline and post-cannabis in a driving simulator.
What this study cannot tell us
Small sample (n = 31). Simulator may not reflect real driving. Only occasional users. Single session.
How to read the evidence
Within-subjects experimental design provides good internal validity but small sample and simulator setting limit generalizability.
When this study was published
Published 2023.
The bigger picture
The absence of speed reduction is concerning because speed is the primary driver-controlled risk factor in crashes.
Questions still open
- Do experienced cannabis users self-regulate better?
- Would real-world driving show different patterns?
Common questions
Do cannabis users drive more carefully when high?
How does cannabis affect driving vision?
Read the original research
Self-Regulation of Driving Behavior Under the Influence of Cannabis: The Role of Driving Complexity and Driver Vision.
Human factors, 65(7), 1506-1524
Citation
Ortiz-Peregrina, Sonia; Oviedo-Trespalacios, Oscar; Ortiz, Carolina; Anera, Rosario G. (2023). Self-Regulation of Driving Behavior Under the Influence of Cannabis: The Role of Driving Complexity and Driver Vision.. Human factors, 65(7), 1506-1524. https://doi.org/10.1177/00187208211047799