The number of people being arrested for driving while high on drugs is up 20 percent in Georgia in the past five years.

WSB went to Colorado -- where marijuana use is legal -- to see how officers are cracking down on people driving while high.

Colorado voters approved the use of recreational marijuana a few years ago. Since then, more people are smoking marijuana and eating edibles, and then getting behind the wheel.

"I've seen somebody driving down the road hitting a bong before," a man who works in the marijuana industry told WSB.

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Cpl. Roger Meyers, a Colorado State Patrol officer who has been trained as a drug recognition expert, said when he suspects someone is driving while impaired by marijuana, he starts a conversation with the person.

"How much cannabis have you smoked tonight or how much cannabis have you used tonight?" Meyers said.

Meyers responded to a call about a pickup truck going 100 mph and weaving through traffic without its headlights on. Officers initially suspected the driver might be high on marijuana, but after spotting an open container of beer in his truck, they arrested him for driving under the influence of alcohol.

Under Colorado law, the legal limit for marijuana use is five nanograms of THC -- five-billionths of a gram.

An estimated 12.4 percent of the deadly crashes in Colorado in 2015 involved a driver who tested positive for cannabis, up 8.1 percent since 2013, according to the Colorado Department of Transportation.

"Now as far as crashes, that's a challenge also, because everybody that's in a crash impaired is required to test, but some people don't test," said Glenn Davis, highway safety manager with the Colorado Department of Transportation.

Davis said anyone who refuses to take a blood test faces losing his or her driver's license for one year.

Colorado is working to change attitudes about driving high, but many people still think it’s OK.

"But if I go to a friend's house and we get high, and I need to get home, I don't think that I'm being unsafe driving," said a man who works in the marijuana industry.

The Colorado Department of Transportation takes a car that fills with smoke to big events and puts up a billboard to warn people that if you drive high, you'll get a DUI.

"Marijuana is fine. Driving with marijuana is not," Davis said.

The Colorado State Patrol is running a pilot program with marijuana DUI devices that test saliva. But there are concerns about those devices.

"Some of those instruments are fairly large and I think that would preclude them being used in a patrol car," Meyers said.

Many of the devices test enzymes that are sensitive to heat and cold.

"If it's below a certain temperature, if it's below freezing, which in Colorado, God forbid, it gets below freezing," Meyers said.

Davis says devices should not replace good old-fashioned law enforcement.

"It's not about a device," Davis said. "Can law (a) enforcement (officer) who stops somebody detect impairment and articulate that impairment?"