By Lemor Abrams

SACRAMENTO (CBS13) — California officials started a new campaign as the state readies for recreational marijuana legalization, but there are questions over how law enforcement can determine if a driver is impaired by pot.

The message is simple: A DUI is about more than just alcohol. Driving under the influence also applies to marijuana, even when it’s legalized starting on Monday.

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The California Office of Traffic Safety launched a new commercial statewide out of fears more marijuana will lead to more accidents.

“If you listen to our counterparts in Washington and Colorado-both have seen serous increases as a result of legalization there,” said Director of CA’s Office of Traffic Safety Rhonda Craft.

“Just like drunk driving, driving under the influence of any impairing substance is not only dangerous, it is a crime,” said California Highway Patrol Chief Brent Newman.

The CHP delivered the message with a sense of urgency, as the agency mourns one of its own.

Officer Andrew Camilleri was killed on Christmas Eve by a driver suspected of being under the influence of both alcohol and marijuana.

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“His passion was going out -doing the job arresting DUI drivers. And he was taken from us from what appears to be a DUI driver,” one of his colleagues said at his bell ringing ceremony.

But as law enforcement issues a stern warning for drivers who feel that they’re OK to get high and drive, they face another challenge: The only tool to test for marijuana is a standard field sobriety test.

CHP Officer Oscar Chavez says, “It’s not specifically for alcohol—when it was developed it involved other drugs including cannabis.”

But a standard breathalyzer, like the one used to test blood-alcohol content on the spot during a traffic stop, won’t determine marijuana intoxication.

Officers say when they pull someone over, they’re not just looking for alcohol.

The ad is already airing in some parts of the state and is expected to run throughout the month of January.

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Meanwhile, CHP will begin its annual maximum enforcement period for New Year’s on Friday, and it will run until Monday.