Among 5,069 injured drivers aged 16-20 at Arizona trauma centers, 19% tested positive for alcohol and 30% tested positive for THC, with substance-positive drivers less likely to wear seat belts or helmets.
Traffic safety researchers, youth health advocates, and policymakers addressing impaired driving.
30% of tested injured young drivers were THC-positive
What the researchers found
Of drivers with BAC results, 19% tested positive (82% of those at or above 0.08 g/dL). Of drivers with THC results, 30% tested positive. American Indians had the highest THC-positive rates (38%) and highest dual positive rates (28%). Substance-positive drivers were less likely to wear seat belts or helmets.
Why it matters
The high rate of THC positivity (30%) among injured young drivers, combined with reduced safety behavior, suggests cannabis-impaired driving is a substantial contributor to youth traffic injuries.
The numbers in context
5,069 injured drivers. 19% BAC-positive (82% at 0.08+). 30% THC-positive. American Indians: 38% THC-positive, 28% dual positive. Annual injured drivers declined 41% over the study period.
How the study worked
Retrospective analysis of 5,069 injured drivers aged 16-20 evaluated at Arizona level 1 trauma centers (2008-2014) using the Arizona State Trauma Registry. Descriptive analysis of BAC and THC test results by demographics and safety behaviors.
What this study cannot tell us
Only injured drivers at level 1 trauma centers, not representative of all young drivers. Not all drivers were tested for both substances. THC presence indicates recent use but not necessarily impairment at time of crash.
How to read the evidence
Moderate: seven-year trauma registry data with biological testing, but limited to one state and level 1 trauma centers.
When this study was published
Published in 2019.
The bigger picture
While alcohol-impaired driving among youth has received decades of public health attention, THC-impaired driving is an emerging concern. The higher THC-positive rate (30%) than alcohol-positive rate (19%) among tested drivers is notable.
Questions still open
- Are cannabis-positive crashes increasing over time? Do cannabis and alcohol have synergistic effects on crash risk? Would targeted prevention for high-risk populations (American Indian communities) reduce these disparities?
Common questions
Does THC-positive mean the driver was impaired?
Why were American Indian drivers disproportionately affected?
Read the original research
Alcohol and marijuana use among young injured drivers in Arizona, 2008-2014.
Traffic injury prevention, 20(1), 9-14
Citation
Shults, Ruth A; Jones, Jefferson M; Komatsu, Kenneth K; Sauber-Schatz, Erin K. (2019). Alcohol and marijuana use among young injured drivers in Arizona, 2008-2014.. Traffic injury prevention, 20(1), 9-14. https://doi.org/10.1080/15389588.2018.1527032