By Joe Vazquez

OAKLAND (CBSF SF) — Alameda County Sheriff Deputy Mathew Neill pulled a driver over in Oakland last month for driving twice the speed limit.

“There’s a strong smell of marijuana coming from this car right now,” the deputy told the driver. “When’s the last time you ingested or smoked weed?.

The driver admitted he had just smoked a blunt. But beyond the smell, how can deputies be sure he is driving under the influence?

A reliable, consistent test to determine whether drivers are intoxicated from smoking pot is a major challenge now facing law enforcement as Californians vote to legalize recreational marijuana.

KPIX5 rode along with a special unit of the Alameda County Sheriff’s Department and observed how they analyze drivers who appear to be intoxicated.

Officers don’t have a device to measure breath or blood. Just a field sobriety test.

They asked a driver to put one foot in front of the other, and walk a line. The driver complies.

Later, deputies pulled over another driver suspected of drunk driving. He clearly stumbled all over the line, and lost his balance. Deputies handcuffed him, but also arrested the first driver who admitted smoking pot. On the surface, the marijuana smoker appeared to pass all their field sobriety tests. But, said Deputy Neill, “his pulse was very elevated.”

In the Bay Area, there is a public perception that driving under the influence of marijuana is not that big a deal. The belief is that people slow down and are thus just not that dangerous.

“That is not true at all,” said Deputy Neill. “I have yet to see someone who drives under the speed limit, 10 or 15 miles under the speed limit, while being under the influence of marijuana.”

That observation is anecdotal. What does the science say? Not much, it turns out.

In Colorado, which has already legalized recreational pot, they do have a blood test, but there are two major problems. The director of Colorado’s Public Health Department says the legal tests of 5 nanograms per milliliter of the chemical THC in the blood can detect whether someone has ingested weed, but it can’t tell when. Marijuana can stay in the human body for weeks. “Someone can have a 5 nanogram level and not be impaired; somebody can have a one or two nanogram level and be impaired”, says Dr. Larry Wolk, Chief Medical and Executive Director of Colorado Department of Public Health . “We need that test that shows impairment levels and not detectable levels.”

The other problem is that jurors are not buying the 5 nanogram blood level as proof that the driver was high. “Jurors are just not convicting people based on that”, says Jim Gerhardt, Vice President of the Colorado Drug Investigators Association.

At UC San Diego’s Center for Cannabis Research, they are aiming for better scientific methods to discern whether someone is driving while high.

Participants in the study either smoke a weak joint, a strong joint, or a placebo. Then, they get behind the wheel in a driving simulator.

“You cannot simply take blood, or take saliva right now, and say whether or not a person is impaired to be on the road, said Tom Marcotte, co-director of the Center for Cannabis Research. “We’re hoping to improve upon that.”

Meanwhile, another question remains: will the streets be more dangerous when pot becomes legal? Beau Kilmer, the Drug Policy Research Center co-director at the Rand Corporation, said more research needs to be done, but it’s possible it could get safer.

“The research is very clear,” Kilmer said. “Driving drunk is worse than driving stoned. However, the bulk of the research suggests that driving stoned is still worse than driving sober.”

So Kilmer said a lot depends on whether people decide to forgo alcohol and smoke pot instead. Or mix the two.

“If we see an increase in the number of people driving under the influence of alcohol and marijuana, we should be worried about traffic safety,” said Kilmer.

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