(NBC News) The legalization of recreational marijuana is spreading, and it could be having an impact on road safety.
That’s the implication in a new report from the Insurance Institute for Highway Safety and Highway Loss Data Institute.
The report analyzed insurance and police data from some of the first states to legalize recreational cannabis, including Colorado, Washington, Oregon and Nevada.
In those states, crashes are up by as much as six percent compared with states where marijuana is illegal.
While drunk driving is widely considered taboo, the same stigma may not exist for driving high.
In a Washington State Roadside Survey, drivers who tested positive for THC were less likely to agree that marijuana impairs driving.
14 percent of drivers with marijuana in their system had a child in the car.
Driving under the influence of marijuana is illegal in all 50 states, but determining impairment continues to be a challenge.
Researchers say states considering legalization should consider the potential impact on highway safety.
Recreational marijuana is pending in New Jersey, New York, New Hampshire and Pennsylvania, with marijuana referendums on the ballot in Michigan and North Dakota this November.
More than 60 percent of Americans say they support marijuana legalization, according to the Pew Research Center.