By JOHN O’CONNOR, AP Political Writer

SPRINGFIELD, Ill. (AP) — Proposed plans for the legalization of recreational marijuana use in Illinois have shifted from “when” to “how.”

Democratic Gov.-elect J.B. Pritzker campaigned on the legalization issue and its corresponding tax revenue of as much as $1 billion a year. And Democratic Illinois House Speaker Michael Madigan is on board .

Two key Democratic lawmakers, Sen. Heather Steans and Rep. Kelly Cassidy, have been meeting with interest groups ahead of the legislative session that begins in January. Both have worked on the issue for years.

Marijuana has been federally outlawed since 1937, but its surrounding stigma has been eased in the past few decades. President Jimmy Carter called for its national decriminalization 40 years ago, and 10 states now allow the recreational use of marijuana after voters in Michigan approved such a measure last month.

Although studies have reached differing conclusions on the impact legalization has on usage rates, advocates contend it stays about the same — those who used it before it was legal are the ones using it after legalization.

“You see some decreases among youth because you’re cutting off their access. The guy slinging weed on the corner in my neighborhood, I’ve never seen him ‘card,’ not once,” Cassidy said. “And you see slight increase in people over 50 because their knees hurt.”

The Steans-Cassidy plan would allow Illinois residents to purchase and possess 30 grams of marijuana for recreational use. Non-residents would be allowed 15 grams.

Law enforcement agencies remain opposed, fearing the law would allow for unregulated home cultivation, increase police officers’ difficulty in recognizing marijuana impairment in motorists and not require dosages on labels in the case of edible products. They also disagree with Cassidy’s assessment that young people wouldn’t have the same access.

“People are saying this (legalization) is inevitable because of the changes in the Legislature and the governor’s chair, and it’s clever on the part of the sponsors to keep repeating that in the hopes that people will believe it,” said Ed Wojcicki, executive director of the Illinois Association of Chiefs of Police. “I don’t know that we should assume that.”

Steans said lawmakers commissioned a study from an economist to get a handle on necessary capacity.

Advocates say the state’s medical cannabis program , adopted in 2014, is highly regarded nationally, and Steans said its tight regulations bode well for the adult-use program. The Department of Public Health administers medical cards for approved patients, while the Illinois Department of Financial and Professional Regulation monitors dispensaries and the Department of Agriculture regulates cultivation sites.

Dan Linn, executive director of the state chapter of the pro-cannabis lobbying group NORML, said cultivation centers have been frustrated because they have more capacity than is currently necessary for as few as 45,000 patients receiving state-approved medical cannabis cards. But that doesn’t mean they have the capacity, nor do the other 56 dispensaries, to meet recreational demand.

“With weekly inspection by the state, we (in Illinois) already have a safe and quality-controlled product,” Linn said.

While proponents believe revenue from legalization would help police agencies better equip officers on the road to judge impaired motorists, Wojcicki said that, currently, only a time-consuming blood test can verify marijuana use.

Studies released separately in October by the National Transportation Safety Board and the Insurance Institute for Highway Safety which found higher rates of traffic accidents in states that have legalized recreational pot.

“We just have to say, are we OK with that?” Wojcicki said.

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