(KAIT/NBC) - Legalized marijuana in Colorado has added a new challenge for police on the lookout for drivers under the influence.
Denver police say more motorists are driving while high.
Denver Police Sgt. Rich Coisman has been with the department's DUI unit since 2008.
He's now part of an all-out effort to stop impaired drivers.
"It can be a little difficult trying to prove that somebody is driving high and is impaired by marijuana, again getting back to alcohol is scientific, validated and accepted by the courts, marijuana, we're just not there yet," Coisman said.
A preliminary study shows nearly 70 percent of Colorado marijuana users admit they've driven under the influence at least once in the past year.
More than 25 percent admit they drive high every day.
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