DENVER -

Marijuana is a hot item in Colorado. There are shortages at some shops, and plenty of supply at others.

But, where do all these people go after they buy weed? What if liquor was selling this fast at every liquor store across the state? No doubt, at least some of the people are getting behind the wheel of a car.

Lt. Mark Drajem has worked in the Denver Police Department traffic unit for more than three decades. He knows all of the signs of an impaired driver.

"Dilation of your pupils going from dark to light, light to dark, (we) do blood pressure tests, a lot of different things to detect what type they think it may be," he said.

A DUI is simply a DUI to most law enforcement, whether it's drugs or alcohol that makes you impaired. But, proving someone is drunk is easier to prove.

"If we suspect that it's alcohol, pretty much we're done there," Lt. Drajem said. "We have that probable cause to make that arrest for alcohol. If we suspect it may be drugs, we have to do further testing which can take up to about two hours to complete."

The Denver Police Department also added several more officers three years ago when medical marijuana became legal in Colorado.

"We ramped up our efforts to combat what we thought was going to be an increase in stoned driving. That actually never came to fruition like we thought it would be," Lt. Mark Drajem said.

Surely with 40 plus recreational shops around the state and people coming to Colorado specifically to smoke marijuana, stoned drivers would take over the roads right? Once again, not the case.

"We were anticipating a huge increase that we didn't get. So we still have that staffing on board ready for the commercial sales," Lt. Mark Drajem said.

Troopers in Colorado and Washington says nothing's really changed for them. They're all trained to detect impaired drivers, whether it's alcohol, marijuana, or something else.

At least for now in Denver, drugged driving doesn't appear to be a major problem.

"People we arrest, who we think have been driving while impaired, about three percent of them have only drugs on board. Whether that be THC, whether that be anti-depressant, whether that be pills," Lt. Drajem added.

Thursday the WSP sent KXLY the latest numbers of stoned driving cases. They show a slight increase since I-502 passed. In 2009 through 2011, about 20 percent of all blood tests taken by the WSP tested positive for marijuana. In 2012, it was 19 percent. But last year from January through November, that number jumped to nearly 25 percent.

The WSP also said it has started pulling blood during DUI stops more often.