No simple blood or breath test can detect cannabis impairment, law enforcement officials say

In the wake of recent legalization of cannabis sales in California, state law enforcement’s message is clear: Drive high, get a DUI.

But unlike alcohol, which has a .08 percent blood alcohol limit in the state, there is no chemical threshold to mark marijuana impairment for drivers in California.

[related_articles location=”left” show_article_date=”false” article_type=”automatic-primary-section” curated_ids=””]Instead, prosecution for driving under the influence of weed rests almost entirely on patrol officer-observed signs and symptoms, and exams made by specially trained drug-recognition officers after an arrest.

While the National Highway Traffic Safety Administration reported to Congress in July 2017 that setting THC levels for driving “is not meaningful,” some states have set specific limits for THC, the psychoactive chemical in marijuana. In Colorado and Washington state 5 nanograms (5 billionths of a gram) per milliliter of blood marks impairment. In Nevada it is as low as 2 nanograms.

Without a threshold, cannabis DUI cases can be more difficult to prosecute than a DUI for drinking.

“It would be very helpful to have an established blood-THC limit,” said CHP Officer Allan Zang, one of about six officers in the CHP Santa Rosa unit who has gone through the nearly three-week-long drug recognition course. “It wouldn’t just be helpful for us, but for the District Attorney’s Office as well.”

The Sonoma County District Attorney’s Office declined to comment. A spokesman said it was not appropriate to discuss difficulties convicting people of driving high when the office was actively prosecuting those cases.

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The CHP is currently researching the relationship between impairment and THC levels, said Zang, who has been a trained drug recognition expert for 10 years. And while a legal limit would be welcome, for him there’s never much question if a driver is too high to drive or not.

“The effects of marijuana differ from person to person,” he said. “But I don’t think there’s a gray area; someone is either too impaired to drive or not.”

The National Organization for the Reform of Marijuana Laws, which has pushed for the decriminalization and legalization of cannabis since 1970, supports California lawmakers’ decision not to set a THC threshold.

“All the numbers (states have used) are completely arbitrary. They’re pulled out of a hat,” said Paul Armentano, the national deputy director of NORML. “Any proposed threshold for cannabis will inadvertently criminalize individuals who have not broken the law.”

A habitual smoker might never test below 5 nanograms but show no signs of impairment while driving, while a novice user might be significantly impaired after cannabis and still have a relatively low THC level, Armentano said. Police in Sonoma County echoed his statement.

“We know there’s thousands of people driving who smoke marijuana and can functionally operate a vehicle,” said Santa Rosa Police Sgt. Summer Black. “Our job is to take them off the road when they can’t.”

Fullerton Police Officer Jae Song conducts a field sobriety test on a driver suspected of driving while impaired by marijuana. Officer Lenny Ledbetter assisted on the stop. (Bill Alkofer, Orange County Register/SCNG)

Numbers for driving under the influence of cannabis in Sonoma County aren’t clear because local law enforcement agencies do not denote DUIs by drug.

Anecdotally, officials with CHP and Petaluma and Santa Rosa police departments said there hasn’t been a noticeable spike in DUIs where cannabis is the only intoxicant. But DUIs where marijuana is used with other drugs and alcohol are common.

To determine cannabis impairment, the same routine is followed as with impairment of any kind, said Officer Robert Sutherland, one of three drug recognition experts at the Petaluma Police Department.

There’s a reason a driver might catch the attention of an officer: not being able to maintain a lane or consistent speed, stopping at stop lights only to slowly roll forward or not noticing the light turn green, Sutherland said.

Once the traffic stop is made, Sutherland looks for other signs of impairment.

“Sometimes they have bloodshot eyes or there’s a pipe packed and ready to go in the center console,” he said.

When there is suspicion of impairment, a roadside sobriety test is requested. Defense attorneys said agreeing to such a test is voluntary.

During a sobriety test, drivers are asked to stand on one leg, look at their foot and count until an officer says stop. Drivers are then directed to take nine steps forward and nine steps back in a straight line. An examination of eye movement follows. The eyes of drunken drivers tend to twitch, while stoned drivers can’t hold their eyes in the cross-eyed position, Sutherland said.

Someone failing these tests is arrested and brought to the police station for further examination before being booked into jail, he said.

The drug recognition exam includes a look at a person’s vital signs: heart rate, blood pressure, body temperature and pupil dilation among others. People arrested for DUIs must also submit to a blood test in California.

Drug recognition experts at California law agencies are trained to spot the influence of specific drugs and the combination of intoxicants through physical exams and questioning, Sutherland said.

When he went to the drug recognition course in Oakland last year Sutherland had 80 hours of classroom study followed by a few days of exams on local volunteers who were known to police to be regular drug users.

While Sutherland is an 11-year veteran, he’s been the DUI specialist for eight months. In that time he hasn’t made an arrest for driving under the influence solely of cannabis.

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Sutherland wouldn’t say if he thought cannabis DUIs were difficult to prosecute, but said he documents every DUI arrest the same, outlining the reason for the traffic stop, sign and symptoms, and statements made by the suspects.

“Our district attorney’s office wants all the information we can give them,” Sutherland said.

In Santa Rosa, Black notes people are arrested for drunken driving even if their blood alcohol level is below .08 percent. The law is more concerned with driving impaired and not specific level of impairment, she said.

“Prosecuting DUIs for cannabis is difficult,” said Black, who oversees about 10 officers trained in drug recognition.

“But even if they don’t get convicted at least we got them off the road while driving high.”

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