New study finds alcohol may impair driving more than pot

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The influence of marijuana use on people's driving skills is still a subject of debate, and a federal study provides new insights.

The study, conducted by researchers at the National Institute on Drug Abuse, asked a group of cannabis smokers to participate in six 45-minute drives in a simulator, according to Time. Looking at 250 parameters of driving ability, the research team focused mainly on three: "weaving within the lane, the number of times the car left the lane and the speed of the weaving," Time reports.

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The research showed that alcohol had an effect "on the number of times the car left the lane and the speed of the weaving" but marijuana users showed no signs of impairment. The study did find that cannabis users "with blood concentrations of 13.1 ug/L THC" did show increases weaving among drivers. The researchers equated the weaving as comparable to someone with a blood alcohol level of .08 -- the legal limit for drivers in most U.S. states. According to Time, the legal limit for drivers on pot is 5 ug/L (in states where such use is legal), namely Colorado and Washington.

The study’s principal investigator, Dr. Marilyn Huestis, noted that the important takeaway from the study was that they looked “at the concentration of THC in the driver’s system while they were driving,” and most anyone who is arrested for DWI is tested hours after they've been taken into custody.

The other fact that they discovered was the pot and alcohol become more potent when used together. According to the study, drivers who used both were “weaving within the lanes.” This is because smoking pot while drinking increases the THC absorption and makes the high the user is having more intense, Time reports.