The risk of car crashes is rising in states where marijuana has been legalized, according to an influential insurance group’s new report. In a study set for release Thursday, the Insurance Institute for Highway Safety points to traffic accidents rising in states with legal recreational marijuana. “The last thing in the world that we want is to introduce another legal substance where we may be adding to that toll and to the carnage on our highways,” said David Harkey, president of institute. “With marijuana impairment, we’re just now starting to understand what we don’t know.” The study claims that, after sales of recreational cannabis began, collision insurance claims in Colorado, Nevada, Oregon, and Washington State were 6 percent higher than in nearby states where marijuana is still illegal. “The bottom line of all of this is that we’re seeing a consistently higher crash risk in those states that have legalized marijuana for recreational purposes,” Harkey said.