Data from the Colorado State Patrol show that marijuana DUIs dropped 33 percent so far this year compared to the same time last year.
Total DUIs, including alcohol and other drugs, have fallen 21 percent.
The drop began to be noticed in the summer. State Patrol data showed a 21 percent decline in marijuana DUIs in the first half of the year.
The State Patrol can't explain the declines. A spokesman says there are just too many factors to find any one thing driving down the numbers.
Still, the number of fatal crashes caused by drugs and alcohol is up. There have been 20 more fatal crashes compared to last year.