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While several studies show that motorists driving under the influence of cannabis tend to drive slower and more cautiously, recent statistics from the California Highway Patrol show that an increasing number of people in the Greater San Francisco Bay Area are going to jail for being stoned behind the wheel.

The CHP’s Golden Gate Division released statistics this month for Alameda, Contra Costa, Marin, Napa, San Francisco, San Mateo, Santa Clara, Solano, and Sonoma counties showing that DUI arrests---for cannabis use ---are up.

In 2017, the CHP made roughly 3.7 arrests per week for driving under the influence of cannabis. For the first quarter of this year, CHP officers arrested about six people each week.

The CHP says that if the current trends continues, Bay Area arrests for driving under the influence of cannabis will be up by 70 percent by the end of 2018.

There seems to be a number of reasons why. One, critics point out that following legalization police are on the lookout for this particular crime now more than ever.


“One thing that happens after legalization is increased enforcement of driving under the influence of drugs, one possible reason for a jump,’’ said Ellen Komp, the deputy director of California NORML, the non-profit organization which has worked to decriminalize marijuana.

Also, 2017 legislation earmarks $3 million annually for the CHP to train state and local law enforcement officers in drug recognition and impairment.

Still, law enforcement lacks the proper tools to test cannabis impaired drivers. With no reliable chemical test for marijuana impairment, officers rely on the same standard field sobriety tests given to motorists suspected of drunken driving.

“Can they do these multiple things at one time, can they stand on one foot, look at (their) foot and also count out loud?" said CHP officer Vu Williams, who specializes in marijuana detection and enforcement.

While the CHP is quick to point out that driving with any amount of pot in your system is illegal, several studies show that most marijuana-intoxicated drivers show only modest impairments on actual road tests.

A study by the National Center for Biotechnology Information shows that a driver drinking alcohol and driving is 16 times more likely to be in a fatal crash than a sober motorist.

A motorist testing positive for both marijuana and alcohol, is 25 times more likely to have a fatal crash, the statistics show.

But motorists who smoke or ingest marijuana (and don't drink alcohol) increase their chances of having a fatal crash only slightly (under 2 percent).

Furthermore, a 2012 German study found that habitual cannabis users "typically become tolerant to many of the effects of THC that may influence driving behavior to the point where they may operate a vehicle safely."

"Patients who take cannabinoids at a constant dosage over an extensive period of time often develop tolerance to the impairment of psychomotor performance, so that they can drive vehicles safely,’’ the study says.

Also, because pot can be detected in body fluids for days or even weeks after use, both the American Automobile Association and the National Safety Council have come out against states basing marijuana use and driving laws on cannabis-blood-concentration levels.

Even the National Highway Traffic and Safety Administration has conceded in past reports that "it is difficult to establish a relationship between a person’s THC blood or plasma concentration and performance impairing effects.”

Still, driving after smoking or ingesting marijuana has the CHP’s full attention recently after a series of deadly crashes.

Last Christmas Eve, CHP officer Andrew Camilleri was killed when he was rear ended by a car driving more than 100 mph on I-880. Officials said the driver later admitted to using marijuana.

Earlier this month, Dang Nguyen Hai Tran, 21, of San Jose, was arrested on suspicion of driving under the influence of marijuana in connection with a deadly five-car collision near the Stevenson Boulevard exit on northbound Interstate Highway 880 in Fremont.

Three people, including two children, were killed, but Tran has not been charged.

The Alameda County District Attorney's Office says a more extensive investigation and more information is needed from the CHP before prosecutors decide whether to file charges against Tran.

Komp from NORML said an arrest for driving under the influence of marijuana doesn’t necessarily mean there will be a conviction.

“Since there isn’t a good chemical test for marijuana, finding THC in blood, urine or saliva doesn’t necessarily assign crash culpability,’’ she said.