No one knows how big a problem marijuana is on Florida's roads.

The state can't say how many marijuana-related crashes there have been, or how many have died because of them. It doesn't keep that kind of data.

But as lawmakers rolled out the state's medical marijuana system last year, they also funded a $5 million campaign to warn Floridians it's dangerous and illegal to drive while high.

It's called "Drive Baked, Get Busted." And like legalization itself, it has become a flash point.

State Sen. Rob Bradley, R-Fleming Island, who sponsored the 2017 medical marijuana bill, said its goal is to make it clear to medicinal users that — just as with alcohol — they can be arrested for driving while impaired.

"The ad makes it clear that a medical marijuana card is not a get-out-of-jail-free card if you're driving impaired," he said.

Florida for Care executive director Ben Pollara, whose group campaigned for the 2016 constitutional amendment that legalized medical cannabis, said "Drive Baked, Get Busted" isn't an education campaign — it's an anti-marijuana campaign:

"It's high drama, low information," designed to shake people up, Pollara said.

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In the past six months, the Department of Highway Safety and Motor Vehicles has spent $3.2 million on "Drive Baked, Get Busted" billboards, posters and radio and video ads. The state also has bought ads in newspapers, such as the Tampa Bay Times. Officials stopped buying ads last week and will evaluate the campaign by the end of September.

One poster reminds people, "Don't drive on grass," the text overlaid on a roadside lawn with a tire track streaking through it.

The campaign was created even though the state had no data examining the issue. Lawmakers sought to fix that. The 2017 law also called for the state to start tracking the number of marijuana-related DUI citations, accidents and arrests.

Here's what is known: In 2016, impaired drivers killed 671 people in Florida, according to the most recent data available.

• About 42 percent of them — 285 people — were killed by drivers impaired by just alcohol.

• Drivers impaired by drugs alone were responsible for 205 deaths, or about 31 percent. The state doesn't track what type of drug was used, however.

• Those who were both drunken and high were blamed for 27 percent, or 181 fatalities.

The National Highway Traffic Safety Administration has studied impaired driving for decades. The latest study from 2013 and 2014 showed that the number of drivers with THC — the chemical in pot that induces a high — in their systems has risen over the past decade.

The agency said the legalization of marijuana across the country could be why those numbers increased.

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No roadside test can prove that a driver is impaired by marijuana. Nor can technology.

But officers who search for impaired drivers believe they can detect it.

"Roadside, it's super easy," said St. Petersburg police Officer Scott Pierce, who is a trained drug recognition expert in the traffic homicide unit. "We've all seen someone who's high. … It's obvious from the get-go."

Florida Highway Patrol Sgt. Steve Gaskins agreed: "I think an observant officer would not have difficulty detecting impairment."

The first sign, Pierce said, is a driver struggling to multitask. Someone might be driving the speed limit but weaving in and out of their lane. Or they might be able to stay in their lane but go too fast or too slow.

After pulling over an errant driver, officers look for sluggish reactions and slurred speech; dilated, bloodshot or watery eyes; fluttering eyelids and an inability to cross eyes; and the smell of burnt pot or residual bits of it. Many of these signs also are shown in alcohol impairment.

"We're building a case," said Luis Lopez, a retired Jacksonville Sheriff's Office investigator who teaches officers how to detect marijuana-impaired drivers. "We're not telling officers to look for one thing."

If an officer suspects someone of drunken driving, the officer may ask the driver to perform field sobriety exercises, or physical tests. A driver can refuse to do so without penalty.

Then the officer can ask the driver to submit to a Breathalyzer test along with a blood test or a urine test, which the driver can refuse at the risk of a one-year license suspension. A blood-alcohol level of 0.08 percent or greater is the level at which Florida law presumes a driver to be impaired by alcohol.

Testing for marijuana impairment is not so cut-and-dry. Tests can detect THC in blood and urine, but that substance can remain in someone's system for days or weeks. The results also can be challenged in court by defense lawyers.

So that alone cannot prove impairment. Instead, an officer trained as a drug recognition expert can use a 12-step process to determine that a driver is impaired by marijuana, then testify in court about what they observed.

"That's why the signs of impairment from the officer is so important," Lopez said.

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Critics of "Drive Baked, Get Busted" note that the campaign never mentions medical cannabis. Its real target, they believe, is recreational use.

"I'll call it a missed opportunity," said Ron Watson, a lobbyist for doctors in the medical marijuana field. He added: "It minimizes the fact that this truly is medicine."

University of South Florida neurologist Juan Sanchez-Ramos, who has studied the effects of marijuana and drug dependency, said the campaign's target audience — ages 18 to 34 — is laughing at the ads.

"Most people think it's a joke," he said. "They're not educated (by it)."

Even one of the sponsors of the 2017 law that created the campaign doesn't like it: House Majority Leader Ray Rodrigues, the Estero Republican who filed the House version of the bill.

"I would agree with (critics') objection that the campaign does not educate," he said, adding, "This does nothing to articulate how to be compliant with the medical marijuana program in Florida."

So what advice is the campaign missing? Sanchez-Ramos, who is also medical director of 3 Boys Farm, one of the 13 state-licensed marijuana growers, offered these guidelines:

Those who smoke marijuana should not drive for at least two hours. (This method remains illegal, though there's a court fight to allow it.) Those who have consumed it through edibles should wait at least six hours.

Currently, the only legal ways to use the drug medicinally in Florida are through edibles, oils, sprays, tinctures and vaporizers.

Some supporters of "Drive Baked, Get Busted" believe it could help address a future problem: If marijuana is legalized for recreational use, then even more people will get high before they get behind the wheel.

"We know what's coming," Lopez said. "We're not going to see medical for long, so what they're trying to do here is jump the gun."

• • •

Defenders say the need for the campaign is obvious.

State officials fear that many who get behind the wheel don't find using marijuana particularly dangerous.

"Driving high is driving impaired," DHSMV spokeswoman Alexis Bakofsky said. "You can hurt yourself. You can hurt others. You can face serious legal and monetary consequences as a result of a DUI arrest."

The campaign comes at a time when Florida is grappling with how to deal with legalized cannabis.

"This is a new reality for Florida," Bradley said. "Medical marijuana is here in our state, and with it comes understandable questions about how people will be treated under the law."

Marijuana usage may continue to rise, he said, so the campaign can help curb cannabis-impaired driving before it becomes a major problem.

"It's preferable to be proactive," he said.

Technology could one day help solve the problem of detecting marijuana impairment. A lab at the University of Florida, for example, is working with a Canadian company on building the first-ever THC breath test.

For now, though, the FHP's Gaskins said drivers who can legally use medicinal marijuana should treat it like another legal drug: alcohol.

"It's the same thing, bro," he said. "Use it responsibly."

Contact Justin Trombly at jtrombly@tampabay.com. Follow @JustinTrombly.