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Drunk driving much more dangerous than stoned driving, study says

By Oscar Pascual |

Federally-funded research has proven that alcohol has a much more dramatic effect on driving than marijuana.

A study funded by the National Institute on Drug Abuse (NIDA), the Office on National Drug Control Policy, and federal safety regulator, the National Highway Traffic Safety Administration found that alcohol “significantly increased lane departures/minimum and maximum lateral acceleration; these measures were not sensitive to cannabis,” reports CNN.

As for drivers under the influence of cannabis, researchers concluded that they “may attempt to drive more cautiously to compensate for impairing effects, whereas alcohol-influenced drivers often underestimate their impairment and take more risk.”

A test group consisting of 19 adults either inhaled marijuana or drank enough alcohol to reach approximately 0.065% peak breath alcohol concentration, while some were given a placebo. Researchers studied each driver’s 45-minute driving session by calculating the number of times the vehicle swerved out of its lane, weaving inside the lane, and the speed of the car. NIDA believes that the tests used the “most sophisticated driving simulator of its kind to mirror real-life situations.”

“Alcohol, but not marijuana, increased the number of times the car actually left the lane and the speed of the weaving,” researchers said.

Despite delivering a much more mild effect than alcohol, marijuana still impaired the drivers’ peripheral vision, leading to tunnel vision. People driving with blood concentrations of 13.1 µg/L THC showed an increase in weaving within the lane, similar to drivers with the legal blood/alcohol limit of 0.08. Although both alcohol and marijuana caused drivers to weave, only alcohol increased the number of times the car actually left the lane, as well as the speed of the weaving.

Despite marijuana having a less extreme effect on driving than alcohol, stoned driving is still dangerous, and law enforcement are struggling to establish a legal THC limit for drivers.

“THC concentrations drop rapidly during the time required to collect a blood specimen in the U.S., generally within two to four hours,” researchers told CNN, with the concern that implementing driving laws based on THC concentration “will unfairly target individuals not acutely intoxicated, because residual THC can be detected in blood for up to a month of sustained abstinence in chronic frequent smokers.”

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