Erin Fuchs wrote this piece for Business Insider where she is Business Editor. This extract was taken from Slate.com. This article considers the ramifications relating to the legalization of marijuana smoking in Washington and Colorado and the effect on DUI laws.

Come New Year’s Day, Colorado’s pot shops will start selling legal, recreational weed, but there’s still a marijuana law that’s bugging pot advocates—the state’s new marijuana DUI law. Colorado passed a law last spring that presumes you’re too high to drive if you have five nanograms or more of THC per milliliter of blood, even though many experts say there is insufficient evidence to tie that level of THC to impaired driving.

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“We don’t have a consensus as to what levels of THC are consistently correlated with behavioral impairment,” Paul Armentano, deputy director for the pot advocacy group NORML, told me. But, he added, “Marijuana policy has never been driven by science in this country.”

It’s never been legal to drive while you’re impaired by any drug in Colorado, but this is the first time there’s a presumption that a certain level of THC in your blood means you’re high. Since the controversial new limits passed, Denver criminal defense attorney Sean McAllister told me he’s seen an uptick in marijuana-related driving arrests.

Medical pot users also fear getting stopped now since they may have THC levels above the legal limit but don’t feel too high to drive. Teri Robnett—a patient advocate who also has a pot prescription for her Fibromyalgia—told me she’s often over the THC limit because the medical marijuana she takes metabolizes slowly.

“I can pretty much assume that I will always be above five nanograms in my blood,” she said, “but I have no impairment.”

The Rise of Drug-Impaired Driving Laws

Every state in America has a legal driving limit for blood alcohol levels, as well as some type of law regulating drug use and driving. These laws are known as DUID laws, which stands for driving under the influence of drugs. The idea behind these laws is that being high on the road may be dangerous.

“Smoking marijuana has a very negative effect on your ability to operate a motor vehicle,” Gil Kerlikowske, director of the White House Office of National Drug Control Policy, told SF Gate. “It’s quite dangerous to you, your passengers and others on the road.”

Some states like New York have effect-based DUID laws, meaning that you can get in trouble if you’re visibly impaired while driving and provably high on drugs that made you impaired.

Other states have per se drugged driving laws, meaning you can get a DUID if you have a certain level of drugs in your system. Several states have enacted per se laws in recent months, including Washington and Colorado. Other states like Arizona and Oklahoma have “zero tolerance” per se laws. That means you’re toast if you’re caught driving with any amount of illegal drugs in your system.

While Colorado just legalized recreational pot in Nov. 2012, medical marijuana there has been legal there since 2000, and medical-marijuana activists balked at a driving limit for pot in the state when the measure was previously defeated. Before the Colorado DUID bill failed in May 2012, medical marijuana activists argued that five nanograms was too low and that effectively sober people would end up getting arrested, the Denver Post reported.

Read the rest at Slate.comby