FRESNO, Calif. — In a ritual nearly as familiar as Santa Claus and crowded stores, police agencies have again stepped up enforcement of drunken-driving laws this holiday season.

Studies have found sobriety checkpoints reduce alcohol-related crashes because they create awareness about the risk of arrest.

But some public-safety officials say that message might be lost on the group most at risk — young drivers.

Trying to elude arrest for drunken driving, young people use technology to keep each other informed about the location of sobriety checkpoints, said Sgt. Dave Gibeault, head of the Fresno Police Department’s traffic unit.

Tools include Twitter, text messages and an iPhone application specifically designed to identify checkpoints, Gibeault said.

He thinks young people are drinking more, in part because clubs aimed at that population have proliferated — but also because young drinkers can check their cell phones to find out where police are stopping motorists, he said.

His own daughter often sends him text messages about where she’s heard he’s running checkpoints.

On Twitter, drivers can warn each other with tweets listing intersections where police have set up checkpoints.

A dangerous use of technology?

Not everyone is a critic of this new use of technology.

Fresno attorney Brian Andritch sees nothing wrong with efforts to spread the word about checkpoints.

Andritch, who used to prosecute drunken drivers when he worked in the Fresno County District Attorney’s Office, now defends them — and warns others about sobriety checkpoints on Twitter.

“I don’t see how it’s any different than what police are doing in promoting checkpoints,” he said in an interview.

Gibeault said it’s one thing to spread the word about checkpoints in general, which police want. It’s quite another to provide information that might encourage people to drive drunk, he said.

Wayne Ziese, a spokesman for the California Office of Traffic Safety, said he’s heard a lot of stories about young people using technology to avoid drunken driving arrests.

“Young people continue to be the most dangerous drivers,” he said. “They will continue to drink and drive until they have families and realize they have something to lose.”

Ziese said law enforcement hasn’t figured out how to respond to the more immediate and precise information about checkpoints circulating on the Web and via cell phones.

“New technology brings us new challenges, whether it’s warfare or DUII,” Ziese said.

Changing the checkpoints can be a problem, Gibeault said.

Police can’t easily move them once their location has been broadcast, because of legal requirements and the large number of officers and equipment involved, he said.

The purpose of checkpoints

In any case, the purpose of the checkpoints isn’t to take drunken drivers off the road, Gibeault said. The point is preventing them from getting in the car in the first place.

In 2001, experts convened by the Centers for Disease Control and Prevention reached the same conclusion. The group concluded that checkpoints reduced alcohol-related accidents by an average of 20 percent.

“Although checkpoints may remove some drinking drivers from the road, their primary goal is to reduce driving after drinking by increasing the perceived risk of arrest,” the researchers said.

Saturation patrols — in which police focus on troubled areas with a lot of officers on the move — are more effective than checkpoints at catching drunken drivers, Gibeault said.

But he said he remains a strong supporter of checkpoints, even though the number of drunken-driving accidents has gone up during winter holidays in Fresno.

Last winter holiday, motorists charged with driving under the influence were involved in 49 crashes, compared to 36 five years earlier, police figures show.

Some of the increase is likely due to population gains, and the jump would have been higher if not for checkpoints, Gibeault said.

Clovis Police Chief Janet Davis said more people would have been hurt or killed if checkpoints weren’t set up, and police must continue the effort.

“We’re still doing these campaigns because people aren’t getting it,” she said.