NHTSA study shows no increased crash risk from driving high

Published: February 28, 2015

Updated: July 24, 2018

Author: Callum Micucci

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Driving under the influence of marijuana might not increase your risk of having an accident, according to a study released in February 2015 by the National Highway Traffic Safety Administration (NHTSA).

The study found that the increased risk usually associated while driving under the influence of marijuana (as previous studies have concluded) can be explained by demographic variables like age, gender, ethnicity, and alcohol concentration level. When these variables are factored in, there is no increased risk.

In other words, people who choose to drive under the influence of marijuana are already at a higher risk of an accident. For example, drivers who smoke marijuana are usually young and male: a demographic already determined to be at a higher risk.

“There’s a pretty clear accelerating trend of marijuana use among drivers,” the NHTSA’s communications director, Gordon Trowbridge, told USA Today. “There’s more and more of this on the highway and it’s something we know relatively little about.”

The study looked at 3,000 drivers over a 20-month period in Virginia Beach, Virginia and looked at the effects of both alcohol and marijuana. Of course, they found that drivers with alcohol in their system were at a much higher risk of crashing than those without.

Trowbridge said Marijuana is much more complicated than alcohol. The study found that drivers with .08 breath alcohol concentration (BrAC) are at four times the risk of getting into an accident than sober drivers. The risk climbs to 12 times that of sober drivers at .15 BrAC, and at .20, the risk shoots up to around 20 times.

The effects of marijuana, on the other hand, are far less well-known.

Pullman, Wash. police commander Chris Tennant told USA Today that when police suspect the driver is under the influence of marijuana, they do sobriety tests similar to those used when they suspect alcohol intoxication.

However, Tennant said they usually don’t know that drivers are under the influence of marijuana until they pull them over for a different violation. There’s no consistent pattern to driving under the influence of marijuana as there is with alcohol, he said.