CHICAGO (CBS) Would you like to legally light up in Cook County? That’s the question voters will be asked when they go to the polls next week.

Medical marijuana is already legal. CBS 2’s Dorothy Tucker reports on the impact on the roads if pot goes recreational.

Riverside Police Chief Tom Weitzel said he is seeing more pot DUI’s, adding, “It exploded after medical marijuana was approved.”

Of the 113 DUI arrests in 2017, 20 percent were drugged driving, and almost half of those involved marijuana.

“If we make recreational cannabis in Illinois legal, you’re going to see that 20 percent, in my opinion, jump to 30, 35 percent,” Weitzel said.

It happened in Washington State. After years of medical marijuana, the state approved weed for recreational use in 2012. That year, the percentage of drivers involved in fatal crashes who had recently smoked pot was 57 percent. By 2014, the year recreational sales began, the number jumped to 84 percent.

“Legislators need to understand that with that increased accessibility is going to become increased usage, and you’re going to see increased impairment behind the wheel,” said Mark Medalen, who’s with the Washington Traffic Safety Commission.

At the National Advanced Driving Simulator (NADS) in Iowa, researchers are testing how people drive when they’re high.

“What we see here is the driver drifting off the roadway as they’re trying to turn a corner,” Timothy Brown said, a NADS researcher.

And the more pot they consumed, the worse they drove, according to their tests. But, unlike alcohol, where anything over .08 is considered intoxicated, there’s no magic number for pot yet.

“Five nanograms might be an OK level in a certain group of individuals, and it might be very dangerous in another group,” said Gary Milavetz, who’s with the University of Iowa College of Pharmacy.

Michael Mayes, a medical marijuana patient who owns a dispensary, says he would never drive impaired, adding neither should anyone else. “They could have lack of motor functions. They could have mental blocks of sorts.”

Michigan State Police just began testing a roadside device that measures recent use of marijuana in saliva. Trooper Tim Gean says the device, used along with roadside sobriety tests, could make a difference. “It’s another tool for the police to take impaired drivers off the road,” he said.

The testing on the roadside device in Michigan will last until November. Proponents of recreational marijuana believe the increase in traffic fatalities in Washington State is because more drivers are being tested for pot since legalization.

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