Criminal Justice Faculty Publications and Presentations

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Objective: Given the legalization of recreational cannabis in 2012 in Washington State and recent mixed results regarding the effects of cannabis on driver safety, we examine the link between Delta-9-Tetrahydrocannabinols (THC) and driver’s behavior, including speeding and driver errors which may have contributed to a particular fatal crash.

Methods: The current study utilized data from the Washington State Fatality Analysis Reporting System Analytical File (WA FARS) in years 2008-2016. A series of logistic regression were employed to compare THC positive and negative drivers, as well as drivers who tested positive for other intoxicants.

Results: The results of the study were mixed as Delta-9 THC positively predicted speeding, but not other driver errors. Interestingly, Carboxy THC, a non-psychoactive chemical that can be detected for a longer period of time, was a significant predictor of both speeding and driver errors.

Conclusions: This research further demonstrates that cannabis is a risk factor for fatal crashes, though it is not nearly a risk factor of the same magnitude as alcohol. Additional research is needed to better understand why Carboxy THC is a stronger and more robust predictor of poor driving behavior than Delta-9 THC.


© 2019, National Academy of Sciences: Transportation Research Board. Original published version available at

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Transportation Research Record: Journal of the Transportation Research Board





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