Sometimes, they come through DUI checkpoints smoking a joint.
"They'll say, I've got a medical card," said Los Angeles County Sheriff's deputy Sgt. Philip Brooks, of the drivers who get stopped.
"And we'll say, that doesn't matter. Smoke that at home and don't drive."
While they don't all come through checkpoints smoking marijuana, an increased number of motorists are getting caught driving drugged. It's happening at DUI checkpoints on curved roads through Malibu's canyons and it's happening across the state.
"Half of those caught are impaired due to drugs," said Brooks of the Malibu/Lost Hills Station.
"It's hard to say, but the biggest problem right now is medical marijuana," he added. "People seem to think it's a legal substance."
Statewide, one in seven weekend nighttime drivers was found to be under the influence of drugs, according to a recent survey released by the California Office of Traffic Safety.
Of the 1,300 drivers stopped at checkpoints statewide who voluntarily submitted to a breath and/or saliva sample, 7.4 percent tested positive for marijuana and 14 percent for some type of drug, while 7.3 percent tested positive for alcohol, according to the survey.
And, of those positive hits for alcohol, 23 percent also tested positive for at least one drug.
More than a quarter of those drivers who tested positive for marijuana also tested positive for at least one other drug, according to the study.
The results were culled from information taken at checkpoints set up in nine different cities during August and September of this year.
"This federally funded survey is the first of its kind ever undertaken by a state," said Christopher Murphy, director of the Office of Traffic Safety, in a statement. "These results reinforce our belief that driving after consuming potentially impairing drugs is a serious and growing problem."
Because it's the first survey of its kind in California, it's difficult to know if there has been an increase in impaired driving, state officials said. But the National Highway Traffic Safety Administration's (NHTSA) 2007 National Roadside Survey found that one in eight weekend, nighttime drivers tested positive for an illicit drug.
Anecdotally, local law enforcement officials say they too stop more drivers under the influence of everything from cocaine to pot, Vicodin to NyQuil.
"We're not just talking about illegal drugs, but it could be over the counter or prescription," said CHP Officer Leland Tang of the West Hills station.
"They're both equally dangerous," he said of those who drink and drive or use drugs because, "they are both under the mind-set that they are OK to drive.
A new law that begins on Jan. 1 will help CHP officers and law enforcement file DUI arrests in separate categories: alcohol or drugs.
Signed by Gov. Jerry Brown in September, Assembly Bill 2552 will distinguish the offenses of driving under the influence of alcohol, driving under the influence of any drug, and driving under the combined influence of alcohol and any drug.
The categories will help law enforcement gather better data, determine the scope of the problem, help shape policies and laws, and craft better prevention efforts, Tang and others said.
"It's good for us because, prior to AB 2552, there was no way to quantify if someone was driving under the influence of alcohol, drugs, or a combo," Tang said. "With data, we can go to apply for national grants and get special grants to focus on more education. We really need to target the message that this is dangerous behavior."
When AB 2552 was first introduced in March, cannabis activists worried that police would hand out violations to anyone who had any trace of marijuana in the bloodstream, including medical marijuana users who may have used pot days before. Assemblywoman Norma Torres, D-Pomona, who introduced AB 2552, amended the bill to create different categories for drug and alcohol-related DUIs.
With the new law set to roll out, the Office of Traffic Safety and the CHP also will work together to expand programs that will train more officers to become drug recognition experts.
"We will still do the field sobriety test, and going from there, we may call a drug recognition expert," Tang said.
Alcohol-impaired fatalities among vehicle or motorcycle drivers with a blood alcohol concentration (BAC) of 0.08 grams per deciliter or greater has dropped by 14 percent from 924 in 2009 to 791 in 2010. The 2010 figure is the lowest DUI death total ever, according to national figures.
But Tang said as the massive baby boomer generation ages, more of them may be driving under the influence of prescription drugs. That's why an increase in prevention needs to start now, he said.
For now, just the fact that fatalities continue to occur is troubling, Sheriff's Sgt. Brooks said.
"We've had fatalities in Malibu and surrounding areas, by some using illicit drugs and and others abusing pharmaceuticals."
Across the San Fernando Valley, the number of DUI arrests has remained relatively consistent in recent years. So far this year, there have been 2,888 arrests. In all of last year, there were 3,596 total arrests, said LAPD Detective Bill Bustos of the Valley Traffic Division. He said those include arrests of motorists who also were abusing drugs, and the number will likely exceed 3,000 before the year is over.
Bustos said his department is gearing up for a campaign targeting New Year's Eve and drinking and driving. From Thanksgiving until New Year's Day, DUIs are more common.
"We're going the right direction," Bustos said of prevention efforts. "But we have a long way to go before we're satisfied."