Some states put a THC limit on pot-smoking drivers — Here’s why California doesn’t

Under California law, regardless of the legality or illegality of a substance, if a person is under the influence to the point where it becomes a traffic safety concern, it’s a crime. Under California law, regardless of the legality or illegality of a substance, if a person is under the influence to the point where it becomes a traffic safety concern, it’s a crime. Image 1 of / 3 Caption Close Some states put a THC limit on pot-smoking drivers — Here’s why California doesn’t 1 / 3 Back to Gallery

Melanie Brinegar smelled of marijuana, so a Colorado police officer asked her to get out of her vehicle. On the one-legged stand, a routine part of field sobriety tests, she lost her balance after 28 seconds, when she needed to go 30. A drug recognition evaluation that included looking at her vital signs went worse.

Then a blood analysis showed she had 19 nanograms per milliliter of THC in her system, several times the 5 nanogram threshold of the psychoactive ingredient in marijuana that a Colorado jury could use to infer she was impaired behind the wheel.

But she wasn’t, a jury found. Brinegar was acquitted of driving under the influence of marijuana after her 2014 arrest when her attorney, Colin McCallin, successfully argued she was not impaired.

Brinegar was initially pulled over for driving with an expired license tag, not for a moving violation. It was a routine traffic stop until an officer detected the medical marijuana she took that morning to ease the pain of her degenerative disk disease.

“They had no viable proof,” Brinegar recalled in an interview. “I wasn’t weaving. I didn’t miss a turn signal.”

Cases like hers highlight why California will not set a THC level limit for determining marijuana DUIs when pot legalization laws take full effect Monday with the first sales of recreational cannabis in some cities.

Unlike the nationally accepted 0.08 percent blood alcohol concentration limit used in DUI arrests, there’s no scientific consensus on a base blood level of THC that can prove impairment. Studies haven’t been able to determine a correlation between THC levels and an inability to drive safely, according to both the National Highway Traffic Safety Administration and the American Automobile Association.

California’s decision to keep the DUI laws unaltered is a departure from the first states to legalize recreational cannabis. Washington and Colorado have amended their laws to set marijuana limits that carry varying degrees of weight in court.

Driving under the influence of marijuana remains illegal in California and anyone arrested on suspicion of DUI must undergo a blood test. But those expecting specific, numerical marijuana limits won’t find them. People have been convicted of marijuana DUIs long before the implementation of Proposition 64, relying heavily on testimony from arresting officers, and the system will remain the same with the new year.

California courts will continue to seek a totality of evidence to prove driving under the influence of marijuana. Authorities can use blood test results but will have to focus on factors such as an officer’s initial evaluation of the motorist’s driving, the motorist’s appearance, field sobriety tests and the conclusion of a specially trained drug recognition evaluator, said Chris Cochran, assistant director of the California Office of Traffic Safety.

“Basically, it’s pretty well acknowledged that an actual impairment level from marijuana has not been established,” Cochran said. “It’s not as simple as it is with alcohol, where it pretty much reacts the same from person to person.”

Under California law, regardless of the legality or illegality of a substance, if a person is under the influence to the point where it becomes a traffic safety concern, it’s a crime.

That means someone with a valid prescription for a sleeping pill who crashes into a car can be charged with DUI if the court can prove the drug caused impairment. The section of the penal code simply states, “It is unlawful for a person who is under the influence of any drug to drive a vehicle.”

Still, come Jan. 1, smoking or consuming marijuana in any form while driving or riding in vehicles will be banned in California under threat of a $70 fine.

Colorado has what is called a permissible inference law. The law states a jury can infer a motorist is impaired if the person had more than 5 nanograms of THC per milliliter in their blood. But that person, like Brinegar, can still argue in court that she was not under the influence.

Washington state has a stricter rule. Anyone whose blood contains more than 5 nanograms of THC within two hours of driving is guilty of DUI, the law states.

But that approach has fueled opposition. Signs of impairment, not THC levels, should be the basis for DUIs, said Paul Armentano, deputy director of the National Organization for the Reform of Marijuana Laws.

Laws that rely on THC levels “don’t have any basis in science,” he said.

California “has done a lot of the right things,” in part by hiring and training drug recognition evaluators to focus on signs of impairment, Armentano said.

Statewide, about 1,700 drug recognition evaluators work for the CHP and local agencies, according to CHP officials, who stepped up impairment training after the passage of Prop. 64. The evaluators use an exam to determine motorist impairment, looking at the driver’s reflexes, pupil appearance and blood pressure, among other things, after an arrest.

Drivers under the influence of marijuana tend to have dilated pupils and an elevated pulse, although varying strains of the drug can produce different behavior, said CHP Sgt. Oscar Chavez, who has worked as a drug recognition evaluator for 10 years.

“I’ve seen both ends of the spectrum when it comes to cannabis use,” said Chavez. Some motorists are unsteady on their feet and appear lackadaisical, he said, while others are hyper with an elevated blood pressure.

The agency’s push against drugged driving was given added urgency by the death of Hayward CHP Officer Andrew Camilleri, who was killed when a driver crashed into him on Christmas Eve. Investigators suspect the driver was drunk as well as high on marijuana, but he remains hospitalized and has not been charged.

The Office of Traffic Safety expects more impaired drivers on the road with the legalization of recreational pot sales, pointing to studies from other states. California does not track marijuana-related DUI arrests, but officials said 42.6 percent of drivers given toxicology tests after fatal crashes in 2016 tested positive for drugs — up from 26.2 percent in 2006. Marijuana was the most prevalent drug detected.

“No matter why you are using it, whether it’s medicinal or fun or any other reason, you can still get a DUI,” Cochran said. “That’s going to be anybody and everybody.”

Jenna Lyons is a San Francisco Chronicle staff writer. Email: jlyons@sfchronicle.com Twitter: @JennaJourno