SALT LAKE CITY — The number of drivers involved in fatal crashes with detectable levels of marijuana in their system has "skyrocketed" in the past two years, according to a recent report from the Utah Highway Safety Office.

Analysts said marijuana legalization in nearby states is probably partially responsible for the upswing but only one factor in a troubling trend.

"Regardless of the cause, we're very concerned about it," said Utah Highway Patrol Sgt. Christian Newlin, who supervises the office’s breath testing and drug recognition programs.

According to the Utah Highway Safety Office report, the percentage of fatal crashes involving drivers who tested positive for marijuana increased from 6 percent to 15 percent between 2012 and 2015. In raw numbers, that’s a rise from 11 fatal crashes in 2012 to 38 last year.

During the heated medical marijuana debate in the 2016 Utah Legislature, critics often cited fears that legalization would contribute to a rise in drug-impaired driving.

Rep. Lee Perry, R-Perry, said that was one of his biggest concerns going into the session.

A report by the AAA Foundation released Tuesday showing that traffic fatalities involving drivers in Washington with marijuana in their system had doubled between 2013 to 2014 confirms his fears, Perry said.

Washington legalized recreational marijuana use in 2012.

"We don't know all of the ramifications," said Perry, who is also a Utah Highway Patrol trooper. "So to just go in and say, 'Let's just go do it and try' is probably not the wisest policy decision.”

Christine Stenquist, the executive director of Together for Responsible Use and Cannabis Education, or TRUCE, said the data may seem compelling but “doesn’t quite explain everything.”

Marijuana, unlike alcohol, does not have a known threshold at which a driver becomes impaired — something the AAA Foundation noted in its report. Someone with relatively high levels of THC in their blood may be able to drive safely while someone with low levels of THC may be seriously impaired, the researchers wrote.

In addition, detectable traces of marijuana can remain in someone's blood for days or weeks, long after it has stopped being psychoactive. And the majority of drivers in the Washington study who tested positive for THC — the psychoactive compound in marijuana — also tested positive for alcohol or other drugs.

So it’s hard for anyone to say whether marijuana caused any of the crashes in the study, researchers said.

Those are some of the same caveats with the Utah numbers, according to Newlin.

Marijuana was the most common substance found among drug-positive drivers in fatal crashes in Utah, the report found. In the past 10 years, 128 drivers involved in fatal crashes have tested positive for THC, according to report.

Methamphetamines were the second-most common drugs involved, with 74 drivers showing positive results.

Pain medications such as oxycodone, hydrocodone and morphine were detected in drivers in 57 fatal crashes.

Possible reasons

Newlin said part of the increase is likely due to the fact that marijuana use is becoming more common among the general population.

Another factor is that UHP made an effort to train hundreds of troopers in recent years to better detect drug impairment through observations like smell, muscle tremors and behavior.

"The legalization of surrounding states could be a factor in seeing more of it here across state lines," Newlin said, but so could the improved ability of officers to detect and report drug impairment.

The percentage of drivers in fatal crashes who are tested for drugs has increased from 42 percent in 2011 to 62 percent in 2015, according to the report.

And research on whether marijuana increases risk of car crashes is still inconclusive.

NHTSA study

The National Highway Traffic Safety Administration conducted the first large-scale case-control study on the topic last year and found no association between testing positive for THC and crash risk after controlling for age, gender, ethnicity and alcohol concentration level.

The study involved more than 3,000 drivers in car crashes and 6,000 drivers who were not involved in a car crash.

Marijuana use is dangerous because it can impair drivers in similar ways to alcohol — weakening a driver’s motor coordination, attention to surroundings and reaction time, according to Newlin. But different people react to marijuana in different ways, and products can vary widely in their THC content, he said.

Even if marijuana is detected in someone's blood, "it's a huge challenge trying to figure out when someone is impaired," Newlin said.

Stenquist acknowledged that misuse of marijuana can lead to safety issues and said that's why she's advocating for medical cannabis legalization, not recreational legalization.

She argued that reclassifying marijuana from a schedule I to schedule II drug so that more people can conduct research will go a long way toward helping people become comfortable that it can be used responsibly.

Lawmakers agreed on a legal blood alcohol concentration limit of .08 percent "because there were tests done," Stenquist said.

"We have to get to that point with medical cannabis," she said. "We have to get to the point to say this has medicinal viability. We need to research that a little more and figure out what that means." Email: dchen@deseretnews.com Twitter: DaphneChen_

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