Police, prosecutors find fault with legal pot: How do you test drivers for it?

A plan to legalize recreational marijuana leaves some Illinois lawmakers on a collision course with many cops and prosecutors tasked with catching stoned drivers.

"It's a nightmare," McHenry County State's Attorney Patrick Kenneally said of legislation under debate in Springfield. He and other local law enforcement experts worry legalization will embolden more people to drive while high and raise crash rates.

Proving a driver is impaired by marijuana beyond a reasonable doubt is no slam dunk for law enforcement.

While Breathalyzers provide an exact measurement of how drunk a driver is, "the technology doesn't exist" yet for precisely capturing marijuana impairment, Kenneally contends.

And training officers to conduct flawless sobriety tests for weed or buying experimental pot-detection devices is expensive, police say.

"I think some of the lawmakers are out of touch with reality," Des Plaines Police Chief Bill Kushner said.

Supporters of the Senate bill assert that taking marijuana use "out of the shadows" will reduce crime and unjust arrests while emerging tests are proving successful at catching impaired drivers.

Marijuana "is widely available today on the streets funding criminal enterprises," state Rep. Laura Cassidy of Chicago said Wednesday.

"I believe by legalizing it, it will make their jobs easier," she said. "We'll know it's a safer product, it is regulated, it is tested, it is labeled. And it is easier to keep out of hands of young people."

A driver is considered under the influence of marijuana if tests show five or more nanograms of THC concentration in blood or 10 or more nanograms of THC in other bodily fluids, under current state law. THC, or tetrahydrocannabinol, is the active ingredient in marijuana.

But the science of pot impairment is so new it's easily challenged in court, Kenneally said. A National Highway Traffic Safety Administration study shows the drug's effects can be elusive to pin down.

Marijuana can migrate from a person's blood within 30 minutes, and ends up being stored in fatty tissue, the NHTSA reported in 2017. Scientists also found the level of THC in someone's blood and how stoned they are "do not appear to be closely related" in some studies. Meanwhile, a pot user can be most impaired 90 minutes after smoking, experts said.

Cassidy pointed to a recent one-year test in Michigan where state troopers used mouth swabs to obtain fluid from drivers suspected of using marijuana. Cheek swabs are used in California, too. "This is not a mysterious new thing, it's something that's seen as useful and effective," she said.

The test quickly provides a positive or negative result for marijuana, but doesn't indicate the amount in someone's system. Ninety-two tests were conducted and 38 drivers were convicted on charges related to impairment or drug use as of Dec. 20, 2018, in Michigan.

But if a driver refuses to take a swab, officers typically would have to obtain a search warrant, Kushner said, and that's time-consuming.

"In Cook County, you need to get an assistant state's attorney to write it up, review it, and then find a judge to issue it," he said. "I don't know how many judges would be happy to get up at 3 in the morning" in that scenario.

DuPage County Sheriff James Mendrick cautioned that police will need specially trained drug enforcement experts to handle increasing marijuana cases. Training will be expensive and take officers off the street, he said.

"The passage of this law is preceding the technology and enforcement ability. It's moving so fast," Mendrick said.

Cassidy said revenue from the sale of marijuana would help fund the enforcement program and a task force would be established to evaluate new testing technology so "Illinois stays ahead of the curve."

Retired Chicago Police Officer David Franco, a member of the Law Enforcement Action Partnership that supports legalization, agreed.

"Once legalization becomes prevalent around the country, technology will catch up," he said.

Got an opinion on legalizing pot and how we measure impairment? Drop an email to

Gridlock alert:

A new tentacle is being added to the gnarly reconstruction of the Reagan Memorial Tollway (I-88) between I-290 and York Road near Oak Brook. This week, two eastbound lanes will be shifted onto the westbound side. Access to certain exits will be restricted, so watch out for signs and drive carefully.

Tri-State forums:

Share your angst or excitement about the Tri-State widening at upcoming forums by the Illinois tollway. Events are 6 to 8 p.m. and occur: Monday at the Burr Ridge Police Department, 7700 S. County Line Road; Tuesday at the Lipinski Center, 7256 Skyline Drive, Justice; and Wednesday at the Schiller Park Community Center, 4501 25th Avenue.

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