The commission’s recommendation will go to state lawmakers, who will take up the issue when the Legislature convenes next month.
The vote on Friday came as officials seek to address a potential rise in stoned drivers as marijuana stores open across the state.
Since Nov. 20, four pot shops have begun recreational sales in Massachusetts, with a fifth store opening Saturday. Other states that have legalized cannabis have struggled with the thorny legal and public safety issue of impaired driving, as the science of gauging marijuana impairment has not caught up to the increasing legality of the drug.
Walpole police Chief John Carmichael told other members of the commission that his department needs a tool to pressure drivers to take a test; more than half of suspected drugged drivers in his town refuse to cooperate.
But other commission members pointed out that such tests could be unfair to cannabis users who legally used marijuana in the past and aren’t driving impaired. Tests that could detect marijuana impairment — akin to the way an alcohol breathalyzer detects drunkenness — are still three to five years away, officials said.
“We’re putting the cart before the horse,” said Matt Allen of the American Civil Liberties Union, the sole commission member who voted against the recommendation. “It would behoove the state, and be a good way to support the officers, if we were to do some studies that have better scientific methodologies.”
Researchers have found that cannabis can impede key driving skills, such as cognitive functioning, reaction times, and the ability to multitask. Mixing pot and alcohol can be especially dangerous.
Although scientists agree that blood-alcohol content is a valid measure of a person’s drunkenness, there is no consensus about what amount of marijuana in the blood indicates how stoned someone is.
Peter Elikann, the appointee of the Massachusetts Bar Association, initially expressed skepticism about pressuring drivers to take a problematic test, but in the end voted for the measure, saying it was just one piece of evidence.
“It doesn’t carry the day in a trial,” Elikann said. “It’s just one of the factors that would be considered that would be slightly helpful for the prosecution, but it doesn’t deliver the winning blow.”
Law enforcement leaders on the commission agreed they envisioned such tests being part of a list of assessments that drivers face as police try to build a case for impairment.
Of 10 states that allow adult recreational marijuana use, only Massachusetts and Alaska lack laws that penalize drivers who refuse a drug test, according to research by the state Cannabis Control Commission. The states with such laws are Maine, Colorado, California, Michigan, Nevada, Oregon, Vermont, Washington, as well as Washington, D.C.
Mary Maguire, an appointee from the American Automobile Association, urged the commission to think about the message it was sending to drivers.
“There are many people who believe ‘I drive better high,’ and post online about it every day,” Maguire said. “There’s got to be consequences.”