A marijuana grow in Denver.

(Nathaniel Minor/CPR News)

Fewer Colorado motorists have been cited for driving under the influence of marijuana so far this year.  

Colorado State Patrol data shows a 21 percent decline in marijuana DUIs in the first half of the year.  Citations spiked last year, but this year they’ve gone back down. A total of 416 marijuana citations were recorded in 2016 through June, while there’s only been 329 citations in 2017 so far.

Marijuana citations have only been tracked since 2014 so there’s no long-term data. The state patrol did not give a reason for the change in numbers.

DUI attorneys say a statewide ad campaign against marijuana-impaired driving may be helping, along with the rise of ride-hailing services like Uber and Lyft.

Alcohol is implicated in the vast majority of DUIs. But marijuana impairment is difficult to establish because there's still no easy, breathalyzer-type test.