State panel: Science doesn’t support pot limit for drugged driving

Jonathan Oosting
The Detroit News
California Highway Patrol officer Mark Rossetti administers a Breathalizer test to a man at a sobriety checkpoint December 26, 2004 in San Francisco, California.

Lansing — Michigan should not set a strict standard for how much marijuana a driver can have in their system and should instead continue to rely on field sobriety tests to determine drugged driving, according to new recommendations by a state panel. 

Pot advocates wary of testing standards set in other states say the report confirms the unsettled science on marijuana impairment, while law enforcement and prosecutors say it reinforces the importance of officer training to detect signs of drugged driving as Michigan’s new recreational adult-use legalization law is implemented.

The Impaired Driving Commission, created under a 2016 law and appointed by former Gov. Rick Snyder, dove into existing research and found “there is no scientifically supported threshold” to determine the amount of the main psychoactive chemical in marijuana that could conclusively prove impaired driving. 

“There is a poor correlation” between driving impairment and the blood concentrations of delta-9-tetrahydrocannibinol, otherwise known as THC, the six-member commission said in its 24-page report.

The active chemical has a short half-life, meaning levels for any given user may fall by the time blood is tested, the commission said. Conversely, low levels of THC can remain in the system for days, and testing could “falsely conclude that an individual is impaired.”

Regular marijuana users can also build up a “tolerance” to the drug, meaning a single standard for all users may not adequately measure impairment, the report said.

Matthew Abel, a legalization advocate and attorney with the Cannabis Counsel in Detroit, called the report an “honest” assessment of a complex question with no easy answer.

“Those of us who are familiar with cannabis are well aware that it has those qualities,” he said. “Somebody can not smoke for a period of time and just take one hit and be super high, while someone who has been smoking all along might be sober as a judge.”

The report comes as Michigan grapples with the legal ramifications of recreational marijuana legalization, approved last fall by 56 percent of voters, and prepares for pending retail sales that will dovetail with a growing medical pot industry.

As marijuana legalization sweeps the country, six other states have established “per se” THC blood limits as evidence of drugged driving, ranging from 5 nanograms per milliliter in Colorado to 1 ng/ml in Pennsylvania.

But the Michigan commission, which includes a state police expert and toxicologists, warned against setting a similar limit here because of questions over the validity of those standards.

That recommendation is not surprising and “just highlights this idea that the science in this area is really unsettled,” said Muskegon County Prosecutor DJ Hilson, president of the Prosecuting Attorneys Association of Michigan.

“It affirms what we have already started to do since the change in the law, which is essentially try the facts of the case and not be focused on a particular level of THC in a person’s system.”

The prosecutors association and several law enforcement groups opposed the 2018 recreational marijuana ballot measure because of an expectation that more adult use will increase drugged driving numbers.

Michigan's annual drug-related vehicle crashes increased 44 percent from 2013 to 2017, with fatalities up 56 percent over that five-year period, according to the report. 

"That in and of itself should lead the motoring public to the somber realization that drugged driving in Michigan is a real issue and it should be a concern for us all," said former Allegan County Sheriff Blaine Koops, CEO and executive director of the Michigan Sheriffs' Association.

The lack of an established impaired driving standard makes marijuana-based cases “more complex” than drunk driving cases that use blood alcohol content testing results, Hilson said. “It’s going to require our law enforcement partners, I think, to be a little more diligent in their investigation.”

The commission highlighted the work of specially trained drug recognition officers who are sanctioned to administer roadside saliva tests and recommended the state consider mandating a 16-hour advanced roadside training for all licensed officers. 

Chemical testing could help officers establish probable cause to continue drugged driving investigations, but arrests are typically only made after horizontal gaze, walk-and-turn and one-leg stand field sobriety tests, Koops said. 

Marijuana "is a different animal" than alcohol, he said. "It'd sure be nice to establish (a blood level standard) right now, but we can still make the arrest with other elements in place. Let's do it right, and if we're not quite there yet, we'll get there."

Michigan technically has a “zero tolerance” drugged driving law, but the Michigan Supreme Court in 2013 carved out an exception for registered medical marijuana patients by holding that prosecutors must show more than the presence of THC in a user’s system to prove impairment.

That same exemption may apply to adults who legally use marijuana under the new recreational law, according to the commission. Like the medical version, the recreational law prohibits users from driving “under the influence” of the drug but does not define how to measure that.

The zero-tolerance law is “on the books, but it doesn’t have any legal effect,” Abel said. “And one day the courts will explain that to the state police and the Legislature.”

State police say the commission recommendations will not affect planned expansion of a roadside saliva testing program that allows specially trained officers to screen drivers for various drugs, including marijuana.

Critics have also raised questions over the validity of the marijuana saliva test program and intrusiveness of the cotton swab procedure, which began as a pilot in four counties but is poised to go statewide. 

"Preliminary oral fluid drug screening on the roadside has promise as a potential additional tool to aid law enforcement in determining drug impaired driving," Michigan State Police spokeswoman Shanon Banner said in an email. 

"Oral fluid is collected very close to the time the driver was operating a vehicle, which is beneficial because of the rapid elimination phase of THC in blood plasma." 

The impaired driving commission included Michigan State Police Lt. Col. Richard Arnold, registered medical marijuana patient Margeaux Bruner, forensic toxicologist Nicholas Fillinger, traffic safety specialist Carol Ann Cook Flannagan, Michigan State University Pharmacology and Toxicology Professor Norbert E. Kamanski and physician Dr. William Ray Morrone.

Hilson said their recommendations, for the time being, should discourage any attempts to establish a marijuana blood level standard in Michigan.

“I think that was the whole point of this commission was to kind of dig deeper into the weeds, if you will, to see if in fact a set nanogram level was feasible,” he said.

“And this commission of very smart people decided it’s not wise right now for the state to go in that direction, so I’m hoping the Legislature follows the recommendations.”

Koops said he hopes the report encourages lawmakers to provide additional funding to train more officers as drug recognition experts, which requires local agencies to take officers off their regular beats and backfill their shifts.