Too high to drive? Marijuana-friendly Colorado debates blood-level limits.

DENVER — When is someone too stoned to drive?

The answer, it turns out, has been anything but si mple in Colorado, which last fall became one of the first states in the country to legalize marijuana.

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Prosecutors and some lawmakers have long pushed for laws that would set a strict blood-level limit for THC, the key ingredient in cannabis. A driver over the limit would be deemed guilty of driving under the influence, just as with alcohol.

Such legislation has failed several times in recent years in the face of fierce opposition from marijuana advocates and defense lawyers, who claim a one-size-fits-all standard doesn’t work for marijuana because it affects the body differently than alcohol.

On both sides, passions run high.

“I haven’t had a car accident since I was 18, and I’ve had marijuana in my system for most of that time,” said Paul Saurini, 39, one of numerous weed activists, or “wactivists,” who spoke out against setting a firm blood-level limit during a public hearing in the state capital this week.

“We have to create some standards to protect public safety. Not doing so, in my opinion, is reckless public policy,” said John Jackson, the police chief in nearby Greenwood Village. “Any time you legalize things like this, you’ll have more of it on the roadway. If we had vending machines with Oxycontin, there’d be more people on Oxycontin driving on the roadways. And that’s not safe.”

Since the passage of Amendment 64 in November, Colorado has been wrestling with the many questions of how to regulate the new marijuana reality, from how to tax it and monitor its growth to where people can buy it, sell it, smoke it and advertise it.

But drugged driving looms as one of the most critical and controversial issues. The outcome of Colorado’s struggle to shape marijuana-related DUI laws could have far-reaching implications, as a growing number of states approve marijuana for medical use and others consider legalizing the drug altogether.

State Sen. Steve King, a Republican who supports a THC limit, insists that driving high is no different than driving drunk. “You’re a threat and a hazard,” he said. “The consensus should be to err on the side of safety for the traveling public.”

Michael Elliott and other marijuana advocates argue that marijuana affects different people differently, and that setting a THC limit would free prosecutors from having to prove their cases and could lead to wrongful DUI convictions.

“When it comes to criminal law, we err on the side of protecting the freedom of our citizens and holding the criminal justice system to the highest standards of proof,” said Elliott, a lawyer and executive director of the Colorado-based Medical Marijuana Industry Group.

Though research and opinions vary widely, studies have shown that smoking marijuana tends to affect spatial perceptions. Drivers might swerve or follow other cars too closely, as well as lose their concentration and suffer from slowed reaction times. Such findings have led some researchers to conclude that driving high doubles the chances for an accident, and that smoking pot and drinking before driving is a particularly dangerous mix.