Despite a city ordinance legalizing recreational marijuana for adults, Portland police continue to cite people for possessing small amounts of a drug that remains illegal under federal law.

Police are also expressing concern for the first time about the number of drivers who appear to be operating vehicles under the influence of marijuana.

From January through September, police issued 23 marijuana citations – about half as many as the 44 citations issued during the same period in 2014, when the ordinance went into effect. Police issued 33 citations over the same period in 2013, before the ordinance was adopted. Among the 23 most recent citations, 30 percent involved a traffic violation – up from 23 percent in 2014.

“It is troubling that officers continue to encounter individuals impaired by or actively using marijuana while operating a motor vehicle,” Police Chief Michael Sauschuck said in a report that will be presented to a City Council subcommittee Tuesday.

The report comes as debate is heating up both statewide and nationally about the merits of legalizing marijuana for recreational use. Proponents claim marijuana is safer than alcohol, but opponents worry that legalization will increase drug use among minors and lead to more impaired drivers on the road.

In 2013, Portland became the first city on the East Coast to vote in favor of an ordinance making it legal for adults over the age of 21 to possess up to 2.5 ounces of marijuana for recreational purposes. However, Sauschuck said the city’s police officers would continue to enforce state law, which only allows people with a doctor’s recommendation to possess the drug.

Maine decriminalized marijuana possession in the 1970s, making it a civil offense. In 1999, voters approved a measure to allow patients to receive medical marijuana with a physician’s referral. A system of licensed medical marijuana dispensaries began operating in 2011.

Portland Green Independent Committee Chairman Tom MacMillan, who helped spearhead the successful legalization campaign in Portland, said police should be issuing citations only to people who are using marijuana in public and on the roads, because those actions are prohibited under the ordinance.

“Right now officers are violating the city ordinance and not respecting the civil liberties of the people who live and work in Portland,” MacMillan said. “If they were just possessing it, they shouldn’t have been cited under city law.”

The ordinance, adopted by a citizen-led petition in 2013, requires police to issue an annual report detailing enforcement. The council’s Public Safety, Health and Human Services Committee will receive the report.

Sauschuck said the report confirms that police are enforcing state law appropriately.

“I am satisfied that Portland’s officers are mindful of the ordinance, but are also taking appropriate enforcement action when it is warranted,” Sauschuck concluded. “Officers are not seeking out violations of Maine’s civil possession law, nor are they failing to enforce the law when the situation requires it.”

Had police followed the city ordinance, 15 people would have been spared a marijuana citation, since police contact was initially made for a separate offense.

Eleven of those cited for marijuana were arrested on separate charges, including operating under the influence, carrying a concealed weapon, furnishing alcohol to a minor and unlawful possession of drugs.

Seven people were cited after getting pulled over for traffic violations, including erratic operation, expired registration, defective lights and a stop sign violation. In 2014, 10 of the 44 citations issued were the results of traffic stops.

“In those cases, the operator appeared to be impaired to some degree and/or there was a pronounced smell of marijuana within the vehicle,” Sauschuck wrote.

Police depend on direct observations to make traffic-related citations for marijuana because there are no reliable blood or breath tests for marijuana impairment. Highway safety advocates have raised concerns about the lack of an adequate testing mechanism, as more states legalize medical or recreational use of the drug.

So far this year, police issued citations to eight people who were under the age of 21 (three people under the age of 18 and five between the ages of 18 and 20), who are barred from possessing the drug even under the city ordinance.