Cannabis was found in 1 in 10 crash-injured drivers in South Australia, but alcohol was the bigger problem
Among over 1,000 crash-injured drivers, alcohol was involved far more often than cannabis, and more than a third of cannabis-positive drivers were also drunk.
Quick Facts
What This Study Found
Researchers analyzed hospital and forensic data from 1,074 crash-involved drivers and motorcyclists admitted to hospitals in South Australia over three years. About 1 in 5 had blood alcohol above the legal limit of 0.05. Routine drug testing found about 1 in 10 tested positive for drugs, with cannabis being the most common.
A key finding was the overlap: more than a third of cannabis-positive cases also involved alcohol, and when alcohol was present alongside cannabis, blood alcohol levels tended to be very high (above 0.15 g/100 mL). The coroners' reports from fatal crashes showed similar patterns.
The authors concluded that while drug driving is a genuine problem, alcohol remains the primary substance driving road trauma, and roadside drug testing should not come at the expense of random breath testing programs.
Key Numbers
1,074 crash participants studied over 3 years. 1 in 5 had BAC above 0.05. 1 in 10 tested positive for drugs. Over half of drug-positive cases involved cannabis. More than a third of cannabis cases also involved alcohol. BAC in combined cases typically exceeded 0.15 g/100 mL.
How They Did This
Cross-sectional study linking hospital admission data, police crash reports, and forensic blood test results for 1,074 crash participants over three years. A supplementary sample of 135 coroners' reports from fatal crashes was also analyzed.
Why This Research Matters
Understanding the relative contribution of different substances to road crashes helps allocate enforcement and prevention resources effectively. The frequent co-occurrence of cannabis and high-level alcohol use suggests that polydrug impairment, not cannabis alone, may be the more relevant safety concern.
The Bigger Picture
Debates about cannabis-impaired driving often focus on cannabis in isolation, but this study highlights how frequently cannabis and alcohol co-occur in real-world crashes. Policies addressing impaired driving need to account for polydrug use rather than treating each substance independently.
What This Study Doesn't Tell Us
Cross-sectional design cannot establish whether cannabis directly contributed to crashes. THC detection in blood does not necessarily indicate impairment at the time of the crash. The study was limited to South Australia.
Questions This Raises
- ?How much of the crash risk attributed to cannabis is actually driven by concurrent high-level alcohol use?
- ?Would the crash involvement patterns differ if cannabis-only cases were analyzed separately from polydrug cases?
Trust & Context
- Key Stat:
- 1 in 5 crash drivers had illegal BAC; 1 in 10 tested positive for drugs
- Evidence Grade:
- Cross-sectional analysis of hospital, police, and forensic data from over 1,000 crash participants.
- Study Age:
- Published in 2015 using data from 2008-2014 in South Australia.
- Original Title:
- Examination of the role of the combination of alcohol and cannabis in South Australian road crashes.
- Published In:
- Traffic injury prevention, 16(5), 443-9 (2015)
- Authors:
- Baldock, M R J, Lindsay, V L
- Database ID:
- RTHC-00908
Evidence Hierarchy
A snapshot of a population at one point in time.
What do these levels mean? →Frequently Asked Questions
Is cannabis or alcohol more dangerous for driving?
In this study, alcohol was involved in far more crashes and at much higher rates. When cannabis was present, alcohol was also involved more than a third of the time, usually at very high levels.
Does testing positive for cannabis mean you caused a crash?
No. THC can be detected in blood for hours to days after use. A positive test indicates recent use but does not prove impairment at the moment of the crash.
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Cite This Study
https://rethinkthc.com/research/RTHC-00908APA
Baldock, M R J; Lindsay, V L. (2015). Examination of the role of the combination of alcohol and cannabis in South Australian road crashes.. Traffic injury prevention, 16(5), 443-9. https://doi.org/10.1080/15389588.2014.969804
MLA
Baldock, M R J, et al. "Examination of the role of the combination of alcohol and cannabis in South Australian road crashes.." Traffic injury prevention, 2015. https://doi.org/10.1080/15389588.2014.969804
RethinkTHC
RethinkTHC Research Database. "Examination of the role of the combination of alcohol and ca..." RTHC-00908. Retrieved from https://rethinkthc.com/research/baldock-2015-examination-of-the-role
Access the Original Study
Study data sourced from PubMed, a service of the U.S. National Library of Medicine, National Institutes of Health.
This study breakdown was produced by the RethinkTHC research team. We analyze and report published research findings without making health recommendations. All interpretations are based solely on the published abstract and study data.