A new study has revealed a link between states with legalized medical marijuana and a reduction in traffic-related fatalities. The study was conducted by D. Mark Anderson, a Montana State University economics professor, and Daniel Rees, a professor at the University of Colorado Denver.

In looking at state-level data from sources such as the National Survey on Drug Use and Health, Anderson and Rees discovered that states that had legalized medical marijuana saw an average of a 9 percent decrease in traffic deaths.

"We were pretty surprised that they went down," Rees told the Denver Post.

In an attempt to explain the results, Rees said that the passage of medical-marijuana laws likely resulted in young people consuming less alcohol in favor of using marijuana.

"The result that comes through again and again and again is [that] young adults ... drink less when marijuana is legalized and traffic fatalities go down," Rees told the Post.

Anderson, Rees' fellow researcher, told the Missoulian that while the research doesn't prove that smoking marijuana impairs drivers less than alcohol, this is still a possibility.

"It could be that," Anderson told the paper. "We're saying our results would be consistent with that."

But Discover magazine is skeptical of any strong causal relationship between legalized medical pot and traffic deaths.

There isn't crystal-clear evidence that medical marijuana laws actually do get people to smoke more pot—the three states they discuss, Montana, Rhode Island, and Vermont, have widely varying numbers of people signed up for medical marijuana, and although there was an increase in reported marijuana use in two of the states for some age groups, it wasn't huge.

The study also does not look at states that have not legalized medical marijuana.

The research was posted on the Institute for the Study of Labor's website and is under peer review by the Journal of Law and Economics.