SACRAMENTO — Joseph Brenan, a 40-year-old father of four, was changing a flat tire along Interstate 80 near Sacramento last week when he was struck and killed by a passing motorist who had drifted onto the shoulder of the highway.

The California Highway Patrol arrested Brandon Rotolo, 24, on suspicion of driving under the influence of marijuana and vehicular manslaughter.

Brandon Rotolo, 24, has been arrested on suspicion of driving under the influence of marijuana and vehicular manslaughter after he allegedly struck and killed a motorist changing a flat tire along Interstate 80 last week near Sacramento. (Placer County Sheriff’s Department via AP)

The tragic accident is the sort law enforcement officials fear may become more common after California voters in November approved Proposition 64 legalizing recreational pot. When legalization takes effect next year, the state will become the world’s largest cannabis market.

Police across California are scrambling to keep up by increasing training to spot drug-impaired drivers. Their task is made more difficult because, unlike the 0.08 percent blood level for alcohol, there is no presumed level of intoxication in California and drugs affect everyone differently.

But driving impaired remains illegal, no matter the substance.

On Wednesday, police planned a news conference near the Capitol to demonstrate how they currently conduct roadside drugged-driving tests.

Assemblyman Tom Lackey, R-Palmdale, and the California Police Chiefs Association also planned to demonstrate a portable saliva test that proponents said could one day be widely used to screen for the recent use of marijuana and five other drugs.

Lackey, a former California Highway Patrol member, carried a bill two years ago that would have allowed police to swab a suspect’s mouth and use an “oral fluid” device to test for drugs in much the same way officers currently use breathalyzers to test drivers’ blood-alcohol level. The bill died in its first committee.

The devices are being tested in Kern, Los Angeles and Sacramento counties along with states such as Colorado, which also legalized recreational marijuana. Michigan and Vermont recently authorized use of the tests, according to Lackey’s office.

More California police departments are using the saliva tests after a Kern County judge last year accepted the results as evidence in a drugged driving case, said Lauren Michaels, the police chiefs association’s marijuana and drunken driving policy expert.

“It’s an additional tool to be used, but at the end of the day in an arrest you’d get a blood sample to tell the actual levels of each substance,” she said. It currently is a voluntary test in California that drivers can refuse.

Photo slideshow — story continues below

  • California Highway Patrol Officer Gary Martens, right, has CHP Sgt. Jaimi Kenyon, follow his finger during a demonstration of how drivers, suspected of impaired driving, are currently tested, Wednesday, May 10, 2017, in Sacramento, Calif. Three of California's largest counties are testing a device that can detect the presence of drugs in saliva within five minutes. Some officers and lawmakers want the devices used statewide after voters passed Proposition 64 in November, legalizing the recreational use of marijuana. (AP Photo/Rich Pedroncelli)

Other law enforcement and academic experts said there are too many variables in how marijuana and other drugs are consumed and metabolized to rely on a saliva or breath test. They said the best current method is to train law enforcement officers to spot the signs of impairment.

“The science is still developing,” California Highway Patrol Sgt. Glen Glaser said. “The mere presence of a drug should not make a person feel like they’re subject to arrest if they’re not impaired.”

The highway patrol plans to have every road officer trained in advanced roadside drug detection techniques before Jan. 1, said Glaser, state coordinator of the patrol’s drug recognition expert program. The CHP is busy training officers from other law enforcement agencies as well.

Related: Driving while high: What to expect if you’re pulled over • New California bill would ban cannabis use while driving • Assemblyman pushes again for a driving-while-stoned test

Drunken driving tests mainly test physical skills. Drugged driving screening also looks for cognitive changes among 12 different steps.

For instance, suspects are told to tip back their heads and estimate when 30 seconds have passed; some drugs make time seem to slow down while other drugs produce the sensation that time has accelerated, affecting the users’ perception.

The CHP and other agencies also are cooperating with the Center for Medicinal Cannabis Research at the University of California, San Diego. The center is analyzing and trying to improve both the human drug-recognition experts and the saliva testing as part of a two-year, $1.8 million study.

Researchers are giving 180 volunteers marijuana with varying levels of potency, then measuring both their performance in a driving simulator and ways of spotting any impairment.

They also are trying to learn if there is a particular presumptive level of marijuana intoxication that impairs driving, said Thomas Marcotte, the study’s chief investigator and co-director of the research center.

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