Car crash claims are on the rise in three states where recreational marijuana use is legal, according to an insurance study released Thursday.
The Highway Loss Data Institute found collision claims in Colorado, Washington and Oregon rose 2.7 percent when compared with both their own pre-marijuana rates and crash claims in surrounding states where pot is still illegal.
Colorado and Washington became the first states to legalize recreational marijuana use in 2012, opening their first retail stores in 2014 and 2015, respectively. A total of eight states -- and Washington, D.C. -- have legalized recreational pot sales.
Between January 2012 and October 2016, accident claims rose 16 percent in Colorado, 6.2 percent in Washington and 4.5 percent in Oregon, the study found. Insurance industry groups have been closely monitoring claims since 2013, when the number of auto accidents began to rise after more than a decade of steady decline.
"We're concerned about what we're seeing," said Matt Moore, senior vice president of the Highway Loss Data Institute. "We see strong evidence of an increased crash risk in states that have approved recreational marijuana sales."
While the rising number of crash claims couldn't be directly linked to marijuana usage, it indicates a strong correlation between the two, the study found. It's difficult to prove causation, partially because there is not a field sobriety test designed to test drivers specifically for marijuana. Insurance companies have raised distracted driving, road construction and increased miles driven as other possible factors for the rising collision rates.
"We're concerned about impaired driving in general," Moore said. "Marijuana just layers on top of other impairments like alcohol."
Drunk driving remains a major concern on the road, according to Russ Rader, spokesman for the Insurance Institute for Highway Safety, a nonprofit funded by auto insurers.
"While we have proven countermeasures, proven strategies for reducing alcohol impaired driving, there are a lot of unanswered questions about marijuana and driving," Rader said.