The share of Washington state drivers with marijuana chemicals in their bodies in daytime hours increased from about 8 percent to 23 percent after the state legalized the substance, according to a safety lab report. Would similar results be observed in Colorado?

Washington Study Tracks Changes in Unsafe Driving, Views

Where pot becomes legal, drivers’ opinions and use of the drug become reckless, a national safety lab’s research is showing. The study is aimed at understanding and limiting unsafe driving and accidents by pot users.

The Highway Loss Data Institute, the less-famous counterpart of the Insurance Institute for Highway Safety, and several other organizations surveyed drivers in Washington state before and after the state legalized recreational marijuana sales. It found that drivers surveyed in the daytime were more likely to test positive for marijuana after legalization. However, the share of drivers testing positive at night didn’t change, HLDI recently reported. The researchers also observed factors that likely point to a shift in drivers’ attitudes after legalization: The drivers who tested positive were more likely to admit to the researchers that they had used the drug recently than the drivers before legalization. Also, a smaller share agreed that marijuana impairs driving.

Previous research by HDLI shows that states that legalized marijuana sales saw increases in accidents when compared to nearby states that haven’t legalized marijuana. That research examined auto accident records in Colorado, Washington state, and Oregon and found that pot legalization there was associated with a 3 percent increase in crashes.

The increasing number of states legalizing or liberalizing pot usage motivated the researchers to take up the study so they can understand the trend’s effect on crashes. While tests in simulators and on the road show that marijuana can impinge on some aspects of drivers’ abilities, it has been much more difficult to connect pot use and real-world accidents.

Colorado’s Own Quest for Answers

The Colorado Department of Transportation is conducting its own driver survey, called the Cannabis Conversation, to measure attitudes and usage prevalence here.

Colorado legalized the recreational use of pot in 2012, but as with alcohol, it’s illegal to drive while substantially impaired by its effects.

Marijuana-related traffic deaths reached 77 in Colorado in 2016, as measured by pot’s main intoxicating chemical, Delta 9 THC, The Denver Post reported in 2017. About 51 percent of the drivers in those fatal accidents had THC levels higher than the state’s impairment limit.

Another report by the Foundation for Advancing Alcohol Responsibility, an organization supported by the liquor industry, showed that the number of marijuana-related car accident deaths in Colorado rose 48 percent in the three years after the state legalized recreational pot smoking.

Usage and Perception Measured in Washington

During the three survey periods in 2014 and 2015, 2,355 drivers completed questionnaires about their pot usage and perception of the risks of driving after using. Of those, 99 percent gave samples of their spit or blood to test for the main chemical element of marijuana, THC, or its residual traces. Of the drivers tested during daylight, before retail sales began, about 8 percent tested positive for THC, compared with 23 percent six months afterward. Among the drivers surveyed at night, the share testing positive stayed constant at about 20 percent.

A Change in Attitude, Openness

The report showed that those testing positive were more willing to admit to marijuana use in the final survey than in the earlier sessions: Before retail sales began, only about one-third admitted to using pot in the past year, compared with 72 percent in the last session, after marijuana sales had been legalized.

Perceptions about marijuana’s effect on driving also changed among those testing positive for THC, the report says. Before legalization, about 45 percent of them said it impairs their driving. A year after legalization only 17 percent of the users said pot affected driving abilities.

Among those who didn’t test positive for THC, the share who believed pot does affect driving rose from 52 percent to 56 percent.

Angela Eichelberger, an IIHS senior research scientist, said:

“This is very different from what we see with alcohol. Drinking and driving is much more prevalent at night than during the day. … Legalization may have made using marijuana more socially acceptable, so people more readily admit to it.”

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