Car Crash in the Rain (© Reza Estakhrian/Getty Images)Click to enlarge picture

The number of vehicle accidents involving marijuana have increased three-fold in the last 10 years.

When police responded to a five-car crash near Monroe, Washington, last week they wound up arresting a local woman blamed with driving under the influence of marijuana.

A total of 12 people were injured in the accident, but they might count themselves lucky considering the results of a new study published by Columbia University, which finds the number of fatal crashes involving the use of marijuana tripled from 2000 to 2010.

That could raise new concerns about the growing push to legalize weed, a movement that has gained momentum since both Colorado and Washington approved the public use of the drug last year.

Researchers from Columbia conducted toxicological investigations of nearly 24,000 motor vehicle fatalities, concluding that marijuana played at least some role in 12% of those deaths.

The study coincides with other research that raises questions about the use of weed by young people. The National Highway Traffic Safety Administration found in a 2010 survey that one in eight high school seniors admitted driving after smoking marijuana. Federal data meanwhile shows that nearly a half of drivers fatally injured in a crash who tested positive for marijuana were under 25.

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A separate study published last week in the New England Journal of Medicine found that the drug can impair a teen's driving while also lowering IQ. The report by the National Institute on Drug Abuse could generate some controversy because it also claims a potential link to addiction, something legalization proponents have generally discounted.

After decades of ranking marijuana along with some of the hardest drugs available, the federal government has been rethinking its approach to enforcement. That shift coincides with the fact that Barrack Obama has become the first president admitting to openly smoking marijuana as a teen.

Noting that, "I view it as a bad habit and a vice," Obama told The New Yorker magazine "I don't think it is more dangerous than alcohol."

Of course, alcohol has general been considered one of the leading causes of crashes, fatal or not. And after a decades-long crackdown on drunk driving, it has remained a serious problem, according to a study released last month by NHTSA, adding up to around $250 billion in economic losses annually. The total loss from all crashes was estimated at $871 billion.

Whether marijuana will come to have a similar cost is far from certain but new research is underway, with NHTSA and the National Institute on Drug Abuse close to wrapping up a three-year study on the effects of inhaled marijuana on driving performance. The study has been looking at how both low and high doses affect performance, while comparing it against a placebo.

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The study is examining pot's impact on performance, decision-making, motor control and the ability to focus on the task at hand — namely driving.

The researchers are using what has been described as "the world's most advanced driving simulator," which was previously used for alcohol research at the University of Iowa.

Even with only a handful of states making marijuana widely available, NHTSA has already reported that 4% of all drivers had used the drug during the day, 6% at night. And the nighttime figure doubled over the weekend. The rise has coincided with the expansion in the number of legal medical marijuana dispensaries across the country, according to experts.

The new NHTSA study could prove critical in determining whether there is, in fact, a safe level of consumption for drivers using marijuana, much as there is with alcohol.