The Breakdown

Explaining Southern California's economy

High driving: How stoned is too stoned to get behind the wheel?

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Unlike Washington and Colorado, California hasn't yet legalized recreational marijuana use. But the day is coming when a new ballot measure is put before voters, even though the most recent legalization proposition failed in 2010.

We seem to be headed for a world in which the American West is receptive to making pot legal.  There are incentives for states to go down this road, including the ability to tax pot and avoid having to spend much enforcing anti-pot laws (in 2011, I wrote about the economics of legalizing pot).

But what should be done about pot users getting behind the wheel? 

It's against the law to drive while impaired in California, regardless of  the impairing substance — booze, pot, or other drugs.  If you get arrested for driving while stoned, it's up to a blood or urine test to determine whether there's enough THC (Tetrahydrocannabinol, the stuff in cannabis that get users high) present to prosecute.

If California ever follows Washington and Colorado down the path of legalization, some standard will have to be established for how long one should wait after smoking pot to get behind the wheel.

The consumer auto website has taken a look at the issue and articulated a very conservative but prudent standard:

Whether you are trying to avoid drivers who are under the influence of marijuana or trying to avoid your own legal problems, knowing a ''safe'' interval between smoking and driving is wise.

However, there's no agreement on what that interval is.

The National Highway Traffic Safety Administration, on its Web site, states: "Marijuana has been shown to impair performance on driving simulator tasks and on open and closed driving courses for up to approximately 3 hours."

Among the impairments are worse car handling, increased reaction times, impaired estimates of distance, sleepiness, lack of coordination and less vigilance, NHTSA says.

Other expert sources say that 3 hours is not nearly enough time to wait before driving.

So how long should you wait? To avoid being arrested and prosecuted for driving while stoned, Edmunds suggests getting a full night's sleep after toking before operating a vehicle.

Follow Matthew DeBord and the DeBord Report on Twitter. And ask Matt questions at Quora.

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