According to a recent study, fatal car crashes involving pot use have tripled in the U.S., contributing to about 40 percent of traffic fatalities in the past decade.

“Currently, one of nine drivers involved in fatal crashes would test positive for marijuana,” says Dr. Guohua Li, director of the Center for Injury Epidemiology and Prevention at Columbia, and co-author of the study.

Researchers from Columbia University’s Mailman School of Public Health gathered data from six states – California, Hawaii, Illinois, New Hampshire, Rhode Island, and West Virginia – that perform toxicology tests on drivers involved in fatal car accidents. This data included over 23,500 drivers that died within one hour of a crash between 1999 and 2010.

The researchers found that drugs played an increasing role in fatal traffic accidents. Drugged driving accounted for more than 28 percent of traffic deaths in 2010, which is 16 percent more than it was in 1999.

The researchers also found that marijuana was the main drug involved in the increase. It contributed to 12 percent of fatal crashes, compared to only 4 percent in 1999.

“If a driver is under the influence of alcohol, their risk of a fatal crash is 13 times higher than the risk of the driver who is not under the influence of alcohol,” Li said. “But if the driver is under the influence of both alcohol and marijuana, their risk increased to 24 times that of a sober person.”

Researchers found that the increase in marijuana use occurred across all ages for males and females.

Jonathan Adkins, deputy executive director of the Governors Highway Safety Association, said that marijuana impairs driving in much the same way that alcohol does.

“This study shows an alarming increase in driving under the influence of drugs, and, in particular, it shows an increase in driving under the influence of both alcohol and drugs,” Jan Withers, national president of Mothers Against Drunk Driving, added.

“It’s a wake-up call for us in highway safety,” Adkins added. “The legalization of pot is going to spread to other states. It’s not even a partisan issue at this point. Our expectation is this will become the norm rather than the rarity.”

Additionally, safety experts say that police do not currently have a device to test for marijuana impairment that is as accurate as the breathalyzer for alcohol, but they expect that development of such devices is accelerating.

Troubling, to say the least.