Accidents & Violence, Author Interviews, Cannabis / 11.05.2016
Traffic Deaths Related To Cannabis Impaired Drivers Doubled After Legalization
MedicalResearch.com Interview with:
Mr. Brian C. Tefft
Senior Research Associate
AAA Foundation for Traffic Safety
MedicalResearch.com: What is the background for this study? What are the main findings?
Response: In December 2012, a new law took effect in Washington state that effectively legalized the possession and use of small amounts of marijuana by adults aged 21 years and older for recreational purposes, and also created a legal limit for driving under the influence of marijuana such that having a concentration of 5.00 nanograms or greater of delta-9-tetrahydrocannabinol (THC, the main psychoactive chemical in marijuana) per milliliter of whole blood while driving in the state of Washington is per se driving under the influence.
Data from population-based surveys indicate that the proportion of Washington state residents who report using marijuana increased after this law took effect; however, not much was known about the impact of this new law on traffic safety in the state. To investigate the traffic safety impact of the new law, we examined drug test results from drivers involved in motor vehicle crashes that occurred in years 2010 – 2014 in Washington and resulted in the death of at least one person within 30 days of the crash. Specifically, we looked at the proportion of all drivers involved in fatal crashes who had detectable THC in their blood at or shortly after the time of the crash, which generally suggests that the driver had used marijuana within the past few hours.
Results showed that from 2010 through 2013, approximately 8-9% of drivers in fatal crashes each year were positive for THC, and that proportion was basically flat from 2010 through 2013. In 2014, the proportion basically doubled, to 17%. Our modelling suggests that an increasing trend in the proportion of drivers who were positive for THC began in late 2013, about 9-10 months after the new law took effect.
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