IIHS and HLDI are set to present two studies Thursday on collision crashes in states where marijuana is legal at the Combating Alcohol- and Drug-Impaired Driving summit at IIHS' Vehicle Research Center in Ruckersville, Va.
"We do not want to see marijuana reach the same level of destruction on our roadways as we have seen with alcohol", said Harkey. The Insurance Institute for Highway Safety study does not go as far as making recommendations, though the National Transportation Safety Board recently did.
In another study researchers compared the number of police-reported crashes from 2012 to 2016 before and after weed hit retail shelves in Colorado, Oregon, and Washington and found a combined 5.2 per cent increase in the rate of crashes per million vehicle registrations, compared to neighboring states that haven't legalized marijuana sales.
Driving under the influence of marijuana is illegal in all 50 states, but determining impairment continues to be a challenge.
New research indicates automobile crashes are up by as much as six percent in the first states to legalize the sale of recreational marijuana. "States exploring legalizing marijuana should consider this effect on highway safety".
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. Harkey told NBC news that it would certainly be new in the game and we're noticing the game in completely wrong way. Twenty-two more states allow medical marijuana.
The studies used raw accident data that did not specify that marijuana involvement, due to inconsistent reporting on this factor.
The driver swerved his pick-up truck into the opposite lane and caused a head-on crash.
The studies do, however, mention that the role of cannabis in these accidents isn't clear as drivers who test positive for drugs are often found with alcohol in their system as well.
"The majority of drug-impaired drivers that are arrested in Colorado, the primary drug that's in there, overwhelmingly, is Cannabis", he said.
"A couple of them (were) directed at federal auto safety regulators to develop common drug-testing standards and toxicology standards that states should develop, and to develop model specifications for basically the drug equivalent of a breathalyzer device, so law enforcement officers can test for drug impairment on the side of the road".
Indeed, IIHS found that drivers are largely unaware of the risks of using marijuana while driving.