A special commission studying what to do about people driving under the influence of marijuana is recommending the state focus on training law enforcement to identify signs of impairment. But that impairment test is controversial, even with a member of the commission recommending it.

There’s no breathalyzer test for marijuana, and the drug can continue to show up in blood tests for days after someone gets high, making it difficult to determine if a driver is impaired.

In itsfinal report, the special commission — made up of 13 members, including several from law enforcement — is recommending the state train police to be so-called Drug Recognition Experts to test drivers for a lack of coordination or other signs of impairment. The commission also recommends that the trained officers should be able to order blood tests and to take away the license of drivers who refuse to be tested. And they encouraged the state legislature to adopt a statute allowing Drug Recognition Experts to testify in court as expert witnesses.

The Executive Director of the Cannabis Control Commission, Shawn Collins, is on the commission.

“I think it’s a tool that we see as potentially valuable if we expanded it and made it more readily available across Massachusetts,” Collins said.

Collins said it could cost as much as $8,000 to train a Drug Recognition Expert, including covering the cost of their time away from the force.

“Especially for small police departments, that’s a lot of money," he said. "So we do hope certainly that revenue that’s generated from the sale of adult-use cannabis can be used.”

The commission also said the legislature should amend the law to allow electronic warrants in order to get blood tests, and that those blood tests should be done by medically trained personnel.

Read more: What Happens When You Get Pulled Over While High?

The commission’s one dissenter on those recommendations was Matt Allen of the American Civil Liberties Union of Massachusetts.

“At the ACLU, we cannot support any policy that would include possible penalties for motorists based on a test that’s not based on evidence or science,” Allen said.

Allen said studies on the program in other states have been flawed, and he wants Massachusetts to support research to scientifically validate it before it's implemented here.

“It’s unfortunate that studies with sound methodologies to validate this [Drug Recognition Expert] exam have never been completed, even though the program was developed nearly 40 years ago,” he said. “This is a threat to the civil liberties of drivers who test positive, even when not impaired.”

Collins defended the roadside tests.

“It’s what we’ve got right now, and I think it’s been proven … to be an effective method to collect information about a motorist that may be impaired when they’re driving or operating a motor vehicle,“ Collins said.

Collins said that information can then be shared in a courtroom for a jury to consider. He said Allen’s point was well taken, though, and that “it’s something we ought to continue to evaluate and scrutinize.”

The state legislature will now consider the findings and the recommendations in the report and determine what new laws might be necessary.