Among adult cannabis users across three U.S. states, earlier age of first use, male sex, and residing in Colorado (where recreational use is legal) were associated with more frequent cannabis use, more driving after use, and more positive perceptions of driving safety after cannabis.
Public health professionals, traffic safety researchers, policymakers, and cannabis users.
Each year of delayed onset: 0.51 fewer use days/month
What the researchers found
Each year of delayed cannabis onset was associated with 0.51 fewer use days/month and a lower proportion of driving-after-use days. Women used cannabis 2.3 fewer days/month and drove after use less often than men. Colorado residents reported the most use days, highest likelihood of driving within 2 hours, and most positive perceptions of safe driving after cannabis.
Why it matters
With cannabis legalization expanding across U.S. states, understanding which factors predict cannabis-impaired driving can help target prevention efforts to the highest-risk groups.
The numbers in context
Each year of delayed onset: -0.51 days use/month, -0.02 proportion driving-after-use days, -0.06 safety perception score. Female vs. male: -2.3 days/month, -0.06 driving proportion, -0.29 safety perception.
How the study worked
Online survey of adults aged 25-40 from Colorado (recreational legal), Illinois (medical legal at time), and Iowa (limited legal) who reported past-year cannabis use. SAS GLMSELECT procedure used for analysis.
What this study cannot tell us
Cross-sectional online survey with self-selected participants. Self-reported driving behavior may be underreported. Cannot determine causation. Only three states compared. Age range limited to 25-40.
How to read the evidence
Multi-state survey with statistical modeling, but cross-sectional design and self-selection limit causal claims.
When this study was published
Published in 2022.
The bigger picture
The finding that living in a legal state correlates with both more use and more positive perceptions of driving safety after cannabis suggests that normalization may affect risk perception, not just access.
Questions still open
- Does legalization cause more permissive attitudes toward impaired driving, or do states with more permissive attitudes legalize first? Would targeted public education campaigns change driving-after-use behavior?
Common questions
Do people in legal states drive more after using cannabis?
Does starting cannabis use later reduce driving risk?
Read the original research
A study of self-reported personal cannabis use and state legal status and associations with engagement in and perceptions of cannabis-impaired driving.
Traffic injury prevention, 23(sup1), S183-S186
Citation
Brown, Timothy; Banz, Barbara; Schmitt, Rose; Gaffney, Gary; Milavetz, Gary; Camenga, Deepa; Li, Kaigang; Brooks-Russell, Ashley; Vaca, Federico. (2022). A study of self-reported personal cannabis use and state legal status and associations with engagement in and perceptions of cannabis-impaired driving.. Traffic injury prevention, 23(sup1), S183-S186. https://doi.org/10.1080/15389588.2022.2124803