As Massachusetts prepares next month to legalize the recreational use of marijuana, police chiefs in a number of cities and towns say they worry the new law will give rise to a wave of impaired drivers — a crime they say is challenging to investigate and prosecute.
“It’s extremely difficult for us,” Hanson Police Chief Michael Miksch said. “There’s no simple test like with OUI-alcohol where we have a breathalyzer. . . . With marijuana there’s no breathalyzer.”
Keeping marijuana users from getting behind the wheel, and arresting and prosecuting those who break that law, topped the concerns of many police officials interviewed by the Globe.
Police chiefs said they also worried about keeping the drug, especially in the edible form, out of the hands of underage users. The chiefs also fear that black markets may emerge once recreational use by adults age 21 and older becomes lawful on Dec. 15. Marijuana shops can open in January 2018.
“There are going to be a bunch of challenges, but we have to deal and prepare for the reality of it,” said Salisbury Police Chief Thomas Fowler. “Question 4 passed.”
Jim Borghesani, a spokesman for the “Yes on 4” campaign, said there’s no evidence marijuana legalization in other states has driven up impaired driving rates. He said research often cited by law enforcement about spikes in impaired driving from Colorado and Washington, which legalized marijuana, isn’t credible.
“I reject any suggestion that they’re going to see an increase in impaired driving,” Borghesani said.
Massachusetts voters approved the ballot initiative this month 54 percent to 46 percent despite opposition from several top state officials, including Governor Charlie Baker, the Massachusetts Chiefs of Police Association, all the state’s district attorneys, and county sheriffs.
The measure maintained some restrictions on marijuana use. Driving while under the influence of marijuana remains illegal and so does public consumption of the drug. People who violate the public consumption law can be fined up to $100, though some communities already have bylaws with stiffer fines.
The law also gives communities the authority to regulate, limit, or prohibit marijuana shops and grants employers the right to maintain its drug use policies. State lawmakers have indicated they will revisit the law as well.
The police chiefs said it’s difficult to determine their level of impairment in drivers. Blood, hair, saliva, or urine samples are required, they said, to measure tetrahydrocannabinol or THC, the chemical that’s mainly responsible for marijuana’s psychoactive effects. But that substance can stay in the body for a long time.
“It’s very difficult to tell when someone uses that drug and how it correlates to their impairment right now,” said Walpole Police Chief John Carmichael. “Now you see what a difficult position the police are going to be in to deal with this.”
Unlike alcohol, there are also far fewer officers trained to detect drivers impaired by drugs, police officials said. Some departments have a few officers trained as “drug recognition experts” while others have none and seek specialists from nearby communities when they stop drivers suspected of being under the influence of drugs.
“We’re probably going to need to expand that role,” said Revere Police Chief Joseph Cafarelli.
In Arlington, Police Chief Frederick Ryan said he would like to have an officer with the specialized training assigned to every shift.
State Police, who patrol Massachusetts highways, said troopers will watch for impaired drivers with road patrols, drug recognition experts, and sobriety checkpoints, said David Procopio, a spokesman.
Borghesani, the legalization spokesman, said police have been worried about the potential for impaired driving increases since marijuana was decriminalized in 2008 but haven’t taken any action. He said technology that can detect recent use of marijuana in drivers will soon be available for sale.
“We support them having the ability to detect actual impairment,” Borghesani said.
In Marshfield, where voters rejected the ballot initiative, Police Chief Phillip Tavares said the community has seen several home invasions related to marijuana in recent years.
“It has resulted in serious injuries and major problems,” Tavares said. “Guns have gone off and people have been tied up.”
He said he also worries about safety risks associated with people growing marijuana in their homes, including faulty wiring on grow lights, the potential for toxic mold from humidity, and dangers posed by chemical solvents used to make hash oil, a widely used cannabis concentrate.
The law allows residents to grow up to 12 marijuana plants per household.
Many police chiefs said it would be difficult to track how many plants people grow unless they receive information about a large-scale operation or come upon them while visiting a residence for other reasons.
“I don’t see how we could do it without a search warrant,” said Fowler, the chief in Salisbury, where voters backed legalization. “There are privacy issues.”
Marijuana also remains illegal on the federal level, and laws forbidding trafficking or sales by illicit dealers remain.
State Police said enforcing such laws will remain a “critical part” of their mission. Mark K. Leahy, executive director of the Massachusetts Chiefs of Police Association, said he expects the black market for marijuana to flourish because consumers will want to buy the product without paying taxes.
“We’ll still be looking for the large-scale operations,” he said.
But Carmichael, the Walpole chief, said those investigations could be challenging. The earlier decriminalization of marijuana and legalization of medical marijuana, he said, has eroded officers’ investigative powers as courts ruled that police can’t initiate searches solely based on smelling the drug or spotting it in plain view.
“Law enforcement has been significantly . . . taken out of this equation,” he said. “We’re putting this on the police without the tools or the ability to deal with it.”