Fatal Crashes Involving Marijuana-Positive Drivers Increased in Colorado After Dispensary Expansion
After medical marijuana became commercially widespread in Colorado in mid-2009, the proportion of fatal crash drivers testing positive for marijuana increased significantly, while no similar change occurred in states without medical marijuana.
Quick Facts
What This Study Found
Using federal crash data from 1994 to 2011, researchers found a significant positive trend in the proportion of drivers in fatal crashes who tested positive for marijuana in Colorado after mid-2009, when commercial medical marijuana became widely available. The change in trend was statistically significant (change = 2.16, p<0.0001).
In contrast, 34 states without medical marijuana laws showed no significant changes in marijuana-positive fatal crash drivers during the same period. Neither Colorado nor the comparison states showed significant changes in alcohol-impaired fatal crash proportions.
The study defined the pre-commercial period as 1994 to June 2009 and the post-commercial period as July 2009 to 2011, using 36 six-month intervals.
Key Numbers
Data: 36 six-month intervals (1994-2011). Change in trend after mid-2009: 2.16 (SE 0.45, p<0.0001) for marijuana-positive drivers in Colorado. No significant change in 34 comparison states. No significant change in alcohol-impaired proportions in either group.
How They Did This
Researchers analyzed data from the Fatality Analysis Reporting System (FARS) across 36 six-month intervals from 1994 to 2011. They compared temporal changes in the proportions of drivers in fatal crashes who were marijuana-positive and alcohol-impaired in Colorado versus 34 non-medical marijuana states. Statistical analysis used interrupted time series methods to detect changes in trends.
Why This Research Matters
This was among the first studies to examine the impact of marijuana commercialization on traffic safety using federal crash data. The finding of increased marijuana-positive fatal crashes after dispensary expansion raised important public health and policy concerns about marijuana legalization and driving safety.
The Bigger Picture
This study contributed to the growing debate about marijuana legalization and traffic safety. While the increase in marijuana-positive drivers in fatal crashes is concerning, interpretation requires caution: testing positive for marijuana does not mean a driver was impaired at the time of the crash, as THC metabolites can persist for weeks.
What This Study Doesn't Tell Us
Testing positive for marijuana does not equal impairment at the time of the crash. THC metabolites can be detected days or weeks after use. Testing protocols varied across jurisdictions and over time. Not all fatally injured drivers were tested for marijuana, and testing rates may have increased after commercialization (detection bias). The study could not determine whether marijuana was a causal factor in the crashes.
Questions This Raises
- ?Does the increase in marijuana-positive drivers reflect actual impaired driving or increased prevalence of marijuana use?
- ?How much of the trend is explained by increased testing?
- ?Would recreational legalization (which followed in 2012) amplify this trend?
Trust & Context
- Key Stat:
- Significant increase in marijuana-positive fatal crash drivers after Colorado dispensary expansion (p<0.0001)
- Evidence Grade:
- This is a well-designed ecological time series study using federal crash data and comparison states. However, the marijuana-positive test does not confirm impairment at the time of the crash.
- Study Age:
- Published in 2014 with data through 2011. Colorado subsequently legalized recreational marijuana in 2012, and additional studies have examined the longer-term trends.
- Original Title:
- Trends in fatal motor vehicle crashes before and after marijuana commercialization in Colorado.
- Published In:
- Drug and alcohol dependence, 140, 137-44 (2014)
- Authors:
- Salomonsen-Sautel, Stacy, Min, Sung-Joon, Sakai, Joseph T, Thurstone, Christian, Hopfer, Christian
- Database ID:
- RTHC-00860
Evidence Hierarchy
Follows a group of people over time to track how outcomes develop.
What do these levels mean? →Frequently Asked Questions
Does testing positive for marijuana mean the driver was high?
No. THC metabolites can remain detectable in blood for days or weeks after use. A marijuana-positive test means the driver used marijuana at some point before the crash, but does not confirm impairment at the time of driving.
Could increased testing explain the trend?
Possibly in part. As marijuana became more prevalent and discussed, law enforcement and coroners may have tested for marijuana more frequently after 2009. The study could not control for changes in testing rates.
Read More on RethinkTHC
Cite This Study
https://rethinkthc.com/research/RTHC-00860APA
Salomonsen-Sautel, Stacy; Min, Sung-Joon; Sakai, Joseph T; Thurstone, Christian; Hopfer, Christian. (2014). Trends in fatal motor vehicle crashes before and after marijuana commercialization in Colorado.. Drug and alcohol dependence, 140, 137-44. https://doi.org/10.1016/j.drugalcdep.2014.04.008
MLA
Salomonsen-Sautel, Stacy, et al. "Trends in fatal motor vehicle crashes before and after marijuana commercialization in Colorado.." Drug and alcohol dependence, 2014. https://doi.org/10.1016/j.drugalcdep.2014.04.008
RethinkTHC
RethinkTHC Research Database. "Trends in fatal motor vehicle crashes before and after marij..." RTHC-00860. Retrieved from https://rethinkthc.com/research/salomonsen-sautel-2014-trends-in-fatal-motor
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.