Yahoo Finance 
Auto crashes are on the rise in marijuana states
A new study finds an increase in accident insurance claims in three states that have approved the sale of marijuana for recreational use.
According the Highway Loss Data Institute, the number of vehicle collisions reported to insurance companies in Colorado, Oregon and Washington is 3 percent higher than what would have been expected if those states had not made it legal to buy pot.
"We're concerned about what we're seeing," said Matt Moore, the institute's senior vice president. "We see strong evidence of an increased crash risk in states that have approved recreational marijuana sales."
While Moore's research finds a greater crash risk, his study does not say if the increase in collisions in the three states were directly caused by drivers who were high.
The study also did not look at highway fatality rates in the states that legalized marijuana.
To determine whether collision rates are higher now in Colorado, Oregon and Washington than they would be if recreational pot use was still illegal, the institute compared the collision claim rates before and after legalization with the collision claim rates of comparable states where pot is still illegal. For example, Colorado was compared to Nebraska, Utah and Wyoming.
After crunching the numbers, the institute said collision claims since marijuana was legalized are up 16 percent in Colorado, 6.2 percent in Washington and 4.5 percent in Oregon.
"Colorado has had legal pot sales the longest and it is showing the greatest effect," said Moore. "Meanwhile, Oregon has had pot sales for the shortest amount of time, so its increase is the lowest, but that could change over time."
The study comes as more states are considering legislation to approve pot sales. Opponents say legalization will lead to a number of problems including the increased likelihood of people driving under the influence.
Since Colorado and Washington became the first states to approve cannabis for recreational use, the question of whether high drivers are getting into more accidents has been suggested, but never definitively proven, partially because there is not a field sobriety test to check drivers specifically for marijuana.
Moore said another reason it's hard to determine exactly how many accidents are caused by stoned drivers is that drivers testing positive for having THC often have alcohol in their system as well.
"We're concerned about impaired driving in general," said Moore. "Marijuana just layers on top of other impairments like alcohol."
More From CNBC
