Almost one in seven drivers traveling with children in Washington state tested positive for tetrahydrocannabinol (THC), the psychoactive ingredient in marijuana, according to new research published in the Journal of Studies on Alcohol and Drugs.

The roadside survey set out to examine the prevalence and patterns of alcohol and cannabis use among drivers with children on weekend nights and risk perceptions among these drivers.

A total of 2,056 drivers (1,238 male) participated in the Washington State Roadside Survey between June 2014 and June 2015. Oral fluid, blood, and breath samples were used to measure cannabis and alcohol use.

The results revealed that, compared with other drivers, those who drove with a child were more likely to be driving during the daytime, less likely to be alcohol positive, but as likely to be positive for THC (14 percent compared to 17 percent of those not accompanied by a child).

Researchers also discovered that drivers’ attitudes to marijuana affected their likelihood of driving with a child. Of those who thought marijuana was “very likely” to impair driving, 8.9 percent tested positive for THC. Of those who thought it was “not very likely at all” to impair driving, 40.6 percent tested positive for THC.

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