The IIHS released their findings Thursday.
The report analyzed insurance and police data from some of the first states to legalize recreational cannabis, including Colorado, Washington, Oregon and Nevada.
While this is not confirmed by the news reporters and yet it not proven that this high rate of accidents is because of the legalization of marijuana but caution flags are being raised by the reporters as especially there is no way that could help to test the drivers to make sure that this is the main reason.
IIHS estimates that Colorado, Oregon, and Washington combined saw a 5.2 percent increase in the rate of crashes per million vehicles registered.
Driving while impaired by any substance, including marijuana, is illegal in all states.
Colorado law specifies that drivers with five nanograms of active THC in a milliliter of their blood can be prosecuted for driving under the influence of marijuana.
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"We know a lot of states are considering making recreational marijuana available", Harkey said.
But Harkey admitted that the role that marijuana plays in crashes is much more hard to determine than that of alcohol.
Legalization of recreational use is pending in New Hampshire, New Jersey, New York and Pennsylvania.
Other states where marijuana is allowed for medical use were not included in the study.
The driver swerved his pick-up truck into the opposite lane and caused a head-on crash. "But the rising tide of drug-impaired driving did not begin with this driver, and it will not end with him".
The research notes that determining impairment from marijuana is a tricky task and the drug's role in crashes isn't as clear as the link between alcohol and accidents.
The results were presented yesterday at the Combating Alcohol- and Drug-Impaired Driving summit, hosted by IIHS and HLDI at the Vehicle Research Center in Ruckersville, Virginia.
Among the NTSB's recommendations was one that called for the traffic safety administration to develop specifications for "oral fluid" screening devices that law enforcement can use to test drivers for drug impairment during roadside stops.