Linked crash and toxicology records from Connecticut show that testing positive for alcohol, cannabis, or both significantly increased the odds of driver injury.
Anyone interested in cannabis and driving safety, traffic policy researchers, public health officials
Lack of safety equipment increased severe injury odds nearly 20x
What the researchers found
Drivers who tested positive for alcohol alone, cannabis alone, or a combination of substances had significantly higher odds of injury in motor vehicle crashes. Lack of safety equipment was the single strongest predictor, increasing severe injury odds nearly 20-fold.
Why it matters
Most impaired driving research relies on either crash data or toxicology data separately. Linking these datasets provides a more detailed picture of how specific substances relate to injury outcomes.
The numbers in context
Alcohol alone, cannabis alone, and combinations all significantly predicted driver injury. Lack of safety equipment increased severe injury odds nearly 20 times. Driver errors appeared as protective factors, which the researchers attributed to masking by other variables.
How the study worked
Researchers linked toxicology records (urine, blood, serum, vitreous) with crash data from Connecticut for 2017-2023. They used logistic regression and correlation analysis to identify predictors of driver injury and overall crash severity.
What this study cannot tell us
The study covers a single state (Connecticut) and relies on toxicology data that may not reflect impairment at the time of the crash. The counterintuitive finding about driver errors suggests the model may have confounding issues.
How to read the evidence
Moderate: retrospective analysis linking two administrative datasets with large sample but limited ability to determine impairment timing
When this study was published
Published in 2025 using 2017-2023 Connecticut data
The bigger picture
As cannabis legalization expands, understanding its role in traffic safety requires better data integration. This study demonstrates that linking crash records with toxicology results can improve the analysis of impaired driving.
Questions still open
- How do THC blood levels at the time of crash compare to post-crash toxicology results? Would similar patterns appear in states with different cannabis laws?
Common questions
Does this study prove cannabis causes crashes?
What was the strongest predictor of severe injury?
Read the original research
Integrating crash and fluids toxicology data to examine injury outcomes and associated driver behaviors.
Accident; analysis and prevention, 221, 108200
Citation
Auguste, Marisa E; Pawelzik, Jennifer; Scholz, Caroline. (2025). Integrating crash and fluids toxicology data to examine injury outcomes and associated driver behaviors.. Accident; analysis and prevention, 221, 108200. https://doi.org/10.1016/j.aap.2025.108200