Cannabis users who drive with children don’t always view it as a safety risk

October 18, 2018

(Pacific Institute for Research and Evaluation)
Drivers who agreed to participate in the roadside survey were asked to provide breath, blood and saliva samples for drug and alcohol testing and also answered questions about marijuana use.
Pacific Institute for Research and Evaluation

Prior research suggests that some drivers don't view using marijuana as risky for driving as imbibing alcohol, and those attitudes appear to extend to cannabis users who drive with children, a new study of Washington state drivers shows.

Drivers in the weekend roadside surveys were more likely to test positive for marijuana than alcohol, and almost none of the drivers traveling with a child were alcohol-positive. However, drivers were about equally likely to be marijuana-positive whether or not a child was present. These are the main findings of a new study by the Pacific Institute for Research and Evaluation, the Washington Traffic Safety Commission and IIHS.

The study is based on data collected on weekends in the Washington State Roadside Survey, just before and after retail sales of recreational marijuana began in the state in July 2014. Researchers surveyed drivers three times — in June 2014, November and December 2014, and June 2015. Data were collected on Fridays during the day and night and on Saturday nights.

Teams asked drivers who volunteered for the survey to provide breath, blood and saliva samples for alcohol and drug testing. Volunteers answered questions about their past and current marijuana use and shared their opinions on whether marijuana use impairs driving. Interviewers noted if children who appeared younger than 15 years old were present in the vehicles.

The goal of Washington's roadside survey was to measure the prevalence of THC-positive drivers, as well as drivers' use of alcohol on weekend nights in the state. Tetrahydrocannabinol, or THC, is the primary psychoactive cannabinoid found in marijuana. The roadside survey and initial analysis of the data were funded by the National Highway Traffic Safety Administration and IIHS.

In March, IIHS published a summary of the results before and after legalized retail sales (see "Roadside survey finds changes in pot use, attitudes after legalization," March 29, 2018). Drivers surveyed after retail marijuana sales began were more likely to test positive for marijuana than before, primarily due to a large increase in marijuana-positive drivers during the daytime. Drivers who tested positive for the drug were less likely to agree that marijuana impairs driving.

The latest study examines how more-permissive attitudes about marijuana use and driving might affect child passenger safety.

About 9 percent of the 2,056 drivers age 21 and older in the sample were driving with a child. While almost none of the drivers with child passengers tested positive for any amount of alcohol, 14 percent tested positive for cannabis.

The presence of THC or its metabolites in oral fluid or blood generally indicates recent use of marijuana, but it doesn't necessarily indicate impairment because the chemicals can be detected in the body for hours or, in the case of some frequent users, days.

When queried about their attitudes on marijuana and driving, the majority of drivers said they consider marijuana use "very likely" to impair driving. This was especially the case among drivers traveling with a child. The percent of THC-positive drivers was significantly lower among those who perceived the risk as "very likely" than other drivers. Among this group, 9 percent traveling with a child tested positive for THC, compared with 14 percent of drivers without kids in the car.

Among drivers who said they didn't view marijuana use as a risky driving behavior, 41 percent of those traveling with a child tested positive for THC, compared with 29 percent of those without a child in their vehicle. These differences, however, weren't statistically significant.

"The fact that few weekend drivers with children were alcohol-impaired is good news," says David Harkey, IIHS-HLDI president. "What's concerning, though, is that some drivers may be under the influence of marijuana and traveling with kids in the car. This points to the need to examine driving situations that put children at risk, especially given the trend toward legalizing marijuana."

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