But nobody knows for sure, claims a Michigan state commission that recently recommended that lawmakers not set a marijuana threshold to define drugged driving, akin to the .08 blood alcohol content threshold for drunk driving.
Because the body processes marijuana differently than alcohol, the traditional measurements won’t cut it, the commission concluded.
That means no Breathalyzer or blood limit, and police should continue using roadside sobriety tests, at least until marijuana science and technology catch up to legalization, the commission found.
Six other states with legalized pot have set a blood level for impaired driving. So the Michigan commission’s recommendations may be unsatisfying to marijuana proponents who pushed legalization on the premise it could be regulated like alcohol and for marijuana opponents who feared legalization would wreak public safety hazards on Michigan cities, including a rise in car crashes.
“We want things to look like alcohol… the way that alcohol works with impairment and blood levels of alcohol is convenient” for measurement and enforcement, said Carol Flannagan, a professor at the University of Michigan who specializes in traffic safety and served on the Impaired Driving Safety Commission appointed by former Gov. Rick Snyder to research a THC limit and report back to the governor and Legislature.
Critics say the lack of standards may give too much discretion to police officers, though they agree the state shouldn’t set standards without supporting science. The issue is one of many gray areas Michigan officials are navigating as the state transitions to legal recreational marijuana following voters’ approval of a ballot measure last November.
It’s a world where regulations and scientific research are fumbling to catch up to consumers.
Here’s a look at arguments that frame the issue.
The case against a blood test standard
Unlike alcohol, there isn’t a direct link between how much of marijuana’s intoxicating component, THC, is in drivers’ blood and their level of impairment, said Flannagan.
That’s because pot isn’t linear – there’s a spike in THC levels right after smoking that quickly drops to low levels even though users may feel high for hours, she said. Conversely, traces of pot can be found in users’ blood for days after their high.
So super-stoned drivers can have little THC in their system, while others could be dead sober and show the same amount.
That’s why the report recommends that if police suspect drivers are high, officers should perform the same roadside tests as for drunk drivers.
Among them: Following a light or finger with only eyes; walking heel-to-toe along a line- and standing on one leg for 30 seconds.
These standard tests have “mixed results” for detecting marijuana intoxication, the commission found, but they’re essentially the best option police currently have to test impairment on the roadside.
“It’s a wise recommendation in the sense that science is really unsettled in this area,” said Muskegon County Prosecutor DJ Hilson, president of the Prosecuting Attorneys Association of Michigan.
“For the last several years, we’ve been prosecuting these cases without the use of a (blood THC) level and just relying on the facts of the case to help make that determination.”
Do field tests give police too much discretion?
That’s a “a legitimate concern,” said Brett Rendeiro, an attorney specializing in cannabis law at Butzel Long.
On television, roadside tests involve stumbling drunks falling out of cars in front of police, he said.
“But what about those areas where it’s not so obvious?” Rendeiro said. “Is there potential for the police to allow their prejudices or their mere suspicion to color their subjective determination of whether someone passed a roadside sobriety test?”
Carl Taylor, a professor of sociology at Michigan State University, said “it’s going to be a nightmare, it’s wide open for abuse.”
Neither the public nor police know enough about how legalized marijuana will work in practice, Taylor said, which is a recipe for roadside clashes with cops. “It’s virgin territory.”
Flannagan, the UM professor, said the commission discussed concerns about police subjectivity “extensively.” Until cannabis-specific tests become more reliable, roadside tests are the best option, she said.
In the meantime, the public should have faith in a system that is already used to prosecute impairment cases, she said.
“It’s trust in the system, it’s trust in the test, it’s trust in the process,” Flannagan said.
That’s all the more reason technology needs to catch up, Rendeiro said.
“Communities that are historically marginalized or have concerns about police tactics, this is an area that would be of great concern,” he said.
So now what?
Given the amount of subjectivity, the report recommends state lawmakers invest in police training of stoned driving and research to improve testing technology.
All police officers are required to be trained in the basic roadside sobriety tests, but only 20 percent have advanced training in detecting whether drivers have taken drugs, alcohol and combinations of both, the report says.
Gov. Gretchen Whitmer “recognizes that there still needs to be a process in place to identify impaired driving and protect motorists, and she is ready to work with experts and her legislative partners to get it done,” her spokesman, Robert Leddy, wrote in an email to Bridge.
House Speaker Lee Chatfield has not yet seen the report, spokesman Gideon D’Assandro said. Senate Majority Leader Mike Shirkey did not respond to requests for comment from Bridge.
The Michigan State Police have piloted a roadside spit test for marijuana and other drugs that is promising, Flannagan said. The test is better at determining whether someone used marijuana recently, which would help reduce the chance cops arrest someone who is sober but shows THC blood levels from previous use.
Entrepreneurs in California have also developed a roadside breath test that promises to measure whether someone used cannabis recently. It’s being tested by a few police departments in the region.
“It’s been hard to do research on marijuana because of its status as an illegal drug. So I have some hopes that we can get somewhere” now that it is legal at the state level, Flannagan said.
So how high is too high?
Because everyone metabolizes marijuana differently, there’s no clear guideline such as the one-drink-per-hour rule for alcohol, said Flannagan.
“The best advice that I’ve seen is if you feel different, you drive different,” Flannagan said. “If you are feeling affected by anything you’re ingesting… then it is presumably affecting your cognitive skills that you need to drive.”
Being high on marijuana has been proven to muddle critical driving skills such as reaction time, judgment, anticipation and attention, the report says.
The best rule: Don’t risk it, said Robert Stevenson, executive director of the Michigan Association of Chiefs of Police.
“Don’t smoke and drive. Don’t take a chance with somebody else’s life or your own,” he said.