Colorado State Patrol troopers cited 60 people in January for driving offenses in which marijuana was believed to be involved, a CSP sergeant said last week in reporting the first such numbers in the state.

Trends in stoned driving have proved difficult for state officials to track, and the State Patrol began keeping tallies on impaired-driving cases involving marijuana only in January. In that month, stoned-driving citations made up about 15 percent of the total impaired-driving citations for the month, Sgt. Mike Baker said.

The state is stepping up training so that law officers will be able to spot drivers who are high on marijuana and to differentiate them from drivers who are impaired by alcohol.

"Pot use behind the wheel is really the big bear in the room," Colorado State Patrol Trooper Brian Pettit said. "You know it's there, but nobody wants to touch it."

Pettit is among 25 state troopers who are taking an intensive nine-day course on how to recognize and prosecute drivers under the influence of marijuana.

"In my opinion, I think marijuana-impaired driving is going to become more prevalent, so this was a good opportunity to better detect these things," he said.

When Pettit finishes, he will join 50 other state troopers who are certified as specially trained drug recognition experts (DRE). State and federal officials are pushing to get more DRE officers on Colorado's roads and highways.

The Colorado Department of Transportation used to hold a DRE session once a year. But now, at least one other is scheduled for this year, and more are likely to come to help fill local and state departments with marijuana-detection specialists, said Glenn Davis, program manager for CDOT's office of transportation safety.

DRE candidates will be schooled on the basics of roadside evaluations, including the walk and turn, one-leg stand, and finger-to-nose and eye examinations.

Some of the tests for pot and booze impairment are similar. A Romberg test — maintaining balance with eyes closed — is used to gauge the loss of motor coordination. A suspect also is asked to estimate 30 seconds in his or her head, to gauge the internal clock. Failure of this test can be an indicator of stimulant or depressant use.

Other tests zero in on pot use exclusively. A pot smoker may have a reddish cast to the whites of the eyes, and pupils may be dilated.

The training is needed since stoned driving can be tougher to spot than drunken driving, at least at first glance, he said. "You take the smell of alcohol away, and it's a bit more difficult," Sharp said.

Under Colorado's newest DUI laws, a motorist is presumed to be under the influence of marijuana if the driver's blood contains 5 nanograms or more of active THC (delta-9 tetrahydrocannabinol) per milliliter of blood at the time of driving.

A nanogram is one-billionth of a gram.

But there is no consensus on the exact amount of pot a driver must consume before he or she is considered under the influence. That's because THC is absorbed differently into the bloodstream than alcohol.

DREs are brought into cases once a street officer suspects a motorist is under the influence of cannabis after the roadside tests. Trainers on Monday emphasized the importance of going through a checklist of procedures before putting someone in custody.

"Everything we do is included in each standardized evaluation," said senior instructor and State Patrol Sgt. Rod Noga.