What effect does marijuana legalization have on crash rates?
RALEIGH, N.C. (WNCN)  With more states legalizing marijuana, like neighboring Virginia, theres concern over how that would affect road safety and car crashes. A new study by Insurance Institute for Highway Safety indicated crash rates go up in states where pot is legalized but, its not as simple as that. North Carolina does not keep track of marijuana-impaired driving. It all falls under one statute. A DWI citation would not necessarily capture what the impairing substance is believed to be. That would come out during the course of the court proceedings, said Sgt. Christopher Knox with the North Carolina State Highway Patrol. The laws in other states vary. The recreational use of marijuana and its effect on auto crashes has been studied for several years. The one thing thats been consistent is the spike in crash rates where its been legalized. The latest study by the IIHS looked at insurance industry collision claim data and found a 4 percent increase in crash rates in states that legalized marijuana as compared to states that did not. However, thats not a clear-cut answer. When the IIHS dug deeper into those who were treated at hospitals following crashes, it discovered another factor at play. What we found was it the combination of marijuana and alcohol in peoples systems that was the driving factor behind some of those findings.  Thats hinting that the dual, or poly-substance abuse of marijuana combined with alcohol could be the big issue here and that policy makers may want to consider that. Its important for them to understand the poly-substance abuse issue and its important that we continue to try and address the issue of alcohol impairment, Harkey said. Its really important for policy makers to continue to look for tools that already exist and apply those to the issue of impairment on our roadways.  When it comes to how marijuana affects driving, the IIHS said theres no real-world data on how it changes peoples attitudes behind the wheel  only simulation data. They (drivers) typically respond more slowly and drive more slowly, and they are a little less aggressive, Harkey said. He said more research is needed to understand exactly how marijuana use causes driving impairment either alone or combined with alcohol. Once we understand that, then we can develop tools law enforcement can use to address the problem in the field other than the traditional field sobriety test, Harkey said. More than a third of states have legalized recreational marijuana for adults 21 and older. Recent polls indicate that 68 percent of American adults favor legalization, so the issue of marijuana impairment and driving is one thats going to be one of growing concern.