An interrupted time-series analysis found that cannabis legalization in Uruguay was associated with a 52% immediate increase in light motor vehicle driver fatality rates, particularly in urban settings.
Traffic safety researchers, cannabis policy makers, and countries considering legalization.
52.4% immediate increase in light motor vehicle driver fatalities after legalization
What the researchers found
Following Uruguay 2013 cannabis legalization, light motor vehicle driver fatality rates showed an immediate 52.4% increase (95% CI 11.6-93.3%, p=0.012). The increase was concentrated in Montevideo (urban), not rural areas. Motorcyclist fatality rates were not significantly affected.
Why it matters
As more countries legalize cannabis, understanding traffic safety implications is critical. Uruguay was the first country to fully legalize recreational cannabis, making it a unique natural experiment.
The numbers in context
52.4% immediate increase in light motor vehicle driver fatalities (p=0.012); Montevideo absolute increase of 0.06 per week (p=0.025); no significant change in motorcyclist or rural fatality rates.
How the study worked
Interrupted time-series analysis of weekly traffic fatalities of light motor vehicle drivers and motorcyclists in Uruguay from 2012-2017, comparing trends before and after cannabis legalization.
What this study cannot tell us
Interrupted time-series cannot prove causation; other factors may have changed around legalization; relatively short post-legalization period (2013-2017); ecological design cannot link individual cannabis use to crashes.
How to read the evidence
Moderate: rigorous time-series methodology applied to national data, but cannot prove causation and relies on ecological data.
When this study was published
Published 2020.
The bigger picture
This is one of the first studies examining traffic fatality outcomes following national-level cannabis legalization. The finding of an urban-specific effect on car (but not motorcycle) fatalities suggests a complex relationship that may involve changes in use patterns rather than simple impairment.
Questions still open
- Did the traffic safety effect diminish over time as novelty wore off? Would different legalization frameworks (e.g., stricter impaired driving laws) mitigate the association?
Common questions
Did cannabis legalization increase traffic deaths in Uruguay?
Were all types of drivers affected?
Read the original research
The association between legalization of cannabis use and traffic deaths in Uruguay.
Addiction (Abingdon, England), 115(9), 1697-1706
Citation
Nazif-Munoz, Jose Ignacio; Oulhote, Youssef; Ouimet, Marie Claude. (2020). The association between legalization of cannabis use and traffic deaths in Uruguay.. Addiction (Abingdon, England), 115(9), 1697-1706. https://doi.org/10.1111/add.14994