New research from the Monash University looks at the effect cannabis legalization has on traffic fatalities.

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Three US states have legalized recreational cannabis sales (RCS) so far: Colorado and Washington in 2015, followed by Oregon in 2015. But does the ol’ herb impact traffic fatalities? New research from the Monash University says yes — especially in areas bordering these states.

Cannabis tourism

“The effect of cannabis legalisation on traffic fatalities is a growing public health concern,” says Dr. Tyler Lane, lead author of the study.

“The results suggest that legalising the sale of cannabis for recreational use can lead to a temporary increase in traffic fatalities in legalising states. This spills over into neighbouring jurisdictions through cross-border sales, trafficking, or cannabis tourists driving back to their state of residence while impaired.”

The team calculated a baseline number of deaths resulted from traffic accidents in the three states and nine neighboring jurisdictions — Kansas, Nebraska, New Mexico, Oklahoma, Utah, British Columbia, Oregon, California, and Nevada — prior to legalization.

They compared this with figures of traffic fatalities recorded after legalization to get the number of additional deaths per month compared to states that had not changed cannabis laws. Traffic fatalities increased only temporarily, they report — this increase lasted for about one year following legalization. The study area sums up a population of roughly 27 million people, and saw an additional 170 deaths in the first six months following legalization, the team reports.

However, the team was also surprised to find that neighboring states and provinces saw a slightly larger increase in fatalities than the studied areas. This effect was more pronounced in population centers closest to the border of a legalizing state. The team believes this comes down to cannabis users driving interstate to make purchases before returning under the influence.

This ‘cannabis tourism’ has important implications for both legalizing states and their neighbors, the team explains. Furthermore, the results may be applicable elsewhere, too, as prohibitions against cannabis are lifted.

“Our findings suggest that policymakers should consult with neighbouring jurisdictions when liberalising cannabis policy to mitigate any deleterious effects,” says Dr. Lane.

She adds that these results stand in contrast to research on medicinal cannabis, which suggests it decreases traffic fatalities. One reason for the difference may be that medicinal users tend to substitute cannabis for other substances, including alcohol, which have a greater effect on impairment. Recreational users are less likely to substitute and more likely to combine alcohol and cannabis, which has a much bigger effect than either in isolation.

The paper “Traffic fatalities within US states that have legalized recreational cannabis sales and their neighbours” has been published in the journal Addiction.