By Karen Morfitt

DENVER (CBS4)– The results of a new study show legalized marijuana use is linked to a rise in car crashes in Colorado.

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The Highway Loss Data Institute, a nonprofit research group that publishes insurance loss statistics, released the findings late Wednesday.

(credit: Andrew Caballero-Reynolds/AFP/Getty Images)

Since recreational marijuana was legalized for sale in 2014, the impact on drivers has been unclear.

Colorado State Trooper Josh Lewis with the Colorado State Patrol says for their agency, the data simply isn’t there.

CBS4’s Karen Morfitt interviews State Trooper Josh Lewis (credit: CBS)

“Ultimately when it comes down to its one more thing that we are looking at… but marijuana is not new,” Lewis said.

The Highway Loss Data Institute, however, says their researchers have found a link between legalization and a rise in crashes.

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“Worry that legalized marijuana is increasing crash rates isn’t misplaced,” says David Zuby, Executive Vice President and Chief Research Officer of the Insurance Institute for Highway Safety.

(credit: CBS)

The group looked at collision claims from Colorado, Oregon and Washington before and after retail marijuana became legal.

They compared the numbers with states where its not allowed – factoring in a number of controlled differences including population.

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Colorado saw the biggest estimated increase in claim frequency compared with its control states.

(credit: CBS)

After retail marijuana sales began in Colorado, the increase in collision claim frequency was 14 percent higher than in nearby Nebraska, Utah and Wyoming.

Washington has estimated increase in claim frequency was 6 percent higher than in Montana and Idaho, and Oregon’s estimated increase in claim frequency was 4 percent higher than in Idaho, Montana and Nevada.

“The combined effect for the three states was smaller but still significant at 3 percent,” Moore says. “The combined analysis uses a bigger control group and is a good representation of the effect of marijuana legalization overall. The single-state analyses show how the effect differs by state.”

Jeri Shepherd with Colorado NORML (credit: CBS)

Jeri Shepherd with Colorado NORML, a group advocating for the marijuana industry, questions the group’s methods.

“I see what is called an increase in collision claims but it does not indicate that these claimers are using cannabis themselves or under the influence of cannabis or alcohol or other substances,” Shepherd said.

Because marijuana effects everyone differently, there’s also the question of when someone is considered impaired.

“Part of the problem is they’ll say you find cannabis in somebody’s system that doesn’t mean you’re under the influence,” Shepherd said.

Lewis says for the State Patrol reducing the number of marijuana accidents comes down to education, “People don’t always understand what marijuana can do.”

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Karen Morfitt joined the CBS4 team as a reporter in 2013. She covers a variety of stories in and around the Denver metro area. Connect with her on Facebook, follow her on Twitter @karenmorfitt or email her tips.