(RJ Sangosti, Denver Post file)

Studies offer conflicting conclusions on marijuana legalization’s role in car crashes, fatalities

Hours after one study connected legalized recreational marijuana to an increase in car crash claims, a second study claimed legalization played a less certain role in motor vehicle fatalities.

A study published Thursday afternoon in the American Journal of Public Health concluded that in the three years since Colorado and Washington voted to legalize marijuana for adult recreational use, motor vehicle crash fatality rates increased but were “not statistically different” as compared to those in eight comparable states that had not legalized cannabis.

Early Thursday morning, the Highway Loss Data Institute reported that legal marijuana states Colorado, Oregon and Washington had collision claims rates that were 2.7 percent higher than those rates in neighboring states in the three years since legal sales began.

Although the first-of-their-kind studies landed at differing — and critiqued — conclusions, researchers and industry members alike did come to a consensus on one aspect: More research is needed.

“We believe that an increase in claim frequencies did occur in these state when retail sales began,” said Matt Moore, senior vice president with the Highway Loss Data Institute. “There is a range of results that indicate there’s a need for additional work here.”

The AJPH study was based on U.S. Fatality Analysis Reporting System statistics from 2009 to 2015. Researchers compared year-over-year changes in motor vehicle crash fatality rates — on a basis of per-billion vehicle miles traveled — to rates in Alabama, Indiana, Kentucky, Missouri, South Carolina, Tennessee, Texas and Wisconsin.

Those control states, which have not legalized medical or recreational marijuana, were selected because they exhibited similar traffic, roadway and population characteristics to Colorado and Washington, researchers said in the report.

Prior to legalization, the crash fatality rates were comparable between Colorado and Washington and the control states, according to a draft version of the report provided by the AJPH to The Cannabist.

In the three years after the voter-approved 2012 legalization, researchers noted a difference-in-differences coefficient of 0.2 fatalities per billion vehicle miles traveled — equating to 77 excess crash fatalities, or 2.7 percent, of 2,890 total (and nearly 38 million person-years of exposure), according to the report.

“We do not view that as a clinically significant effect, but others might disagree,” researchers wrote in the report.

Dr. Jayson D. Aydelotte, the lead author on the report, could not be immediately reached for comment Friday or to provide the full report, including supplemental appendices showing additional analysis.

Mason Tvert, spokesman for advocacy group Marijuana Policy Project, said he needed to investigate both studies further, but said legalization’s potential impact on automobile incidents is a complex issue with no simple answer.

It’s a “fool’s errand” ┬áto attempt to conduct before-and-after analysis of legalization’s effect, he said, noting that certain data were not being collected prior to legalization.

“I don’t want to minimize the issue — I think it’s an important issue that needs to be studied,” he said. “Thus far, these studies suggest opponents’ concerns about a doomsday scenario have not materialized; and there’s a need for continued studies.”

Trade group Cannabis Business Alliance didn’t mince words in its criticism of the Highway Loss Data Institute study, claiming that it was “just another attempt to incite reefer madness.”

Interpretations of data aside, statistics tracking the potential effects of legalization are a preliminary baseline in these early years.

Data showing increases in arrests of people suspected of driving under the influence of drugs in Colorado can be misleading, said Mark Bolton, marijuana adviser to Colorado Gov. John Hickenlooper. Following the 2012 passage of recreational marijuana legalization Amendment 64, the state increased funding to train officers on implementing new roadside tests and procedures.

Additionally, while drivers may have THC in their system, it’s less certain to know what extent they’re impaired, he said.

And data do suggest that roadway fatalities have increased between 2013 and today, but those come with caveats as well, Bolton said.

Traffic fatalities in Colorado have been on a six-year rise, according to Colorado Department of Transportation data released earlier this year. The state agency tracked 605 deaths on Colorado roadways in 2016, an increase of 11 percent from the prior year.

Officials did not cite one specific cause for the increase in fatalities, noting contributing factors could include distracted and impaired driving, low seat belt use, and motorcyclists not wearing helmets or other protective gear.

“At least for now, it’s something we’re trying to continue to monitor,” Bolton said.

The Highway Loss Data Institute has initiated a large-scale, case-control study in Oregon to further delve into how legalized marijuana might be affecting the risk of car crashes with injuries, Moore said, adding that his organization will continue to research this topic.

“No single study is ever definitive,” he said. “This is a complex problem, and we’re going to continue to study it.”