Car Crashes Are Up in States With Legal Recreational Marijuana, Study Shows

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A new study shows that in four states that have legalized recreational marijuana, motor vehicle crashes are up 6 percent compared with four neighboring states where marijuana is restricted or illegal. The data suggests that as more states legalize recreational marijuana, more effort will be needed to determine how best to prevent impaired driving crashes.

The study compared insurance claims for vehicle collisions in Colorado, Nevada, Oregon, and Washington—where recreational marijuana is legal—with Idaho, Montana, Utah, and Wyoming—where it is not, and controlled for factors including driver age and employment status, seasonality, weather, and location.

“What we’re seeing is a definite increase in crash risk that is associated with the legalized recreational use of marijuana,” said David Harkey, president of the Insurance Institute for Highway Safety (IIHS) and Highway Loss Data Institute (HLDI), the safety agencies that conducted the research.

Harkey cautioned that the study results indicate only a correlation between marijuana legalization and a higher number of crashes, and that more research would be necessary to determine whether marijuana use caused the increase. Still, he said the results are reason for concern. 

“Impairment is impairment, whether it’s alcohol or marijuana or prescription drugs,” Harkey told CR. “Any of those can affect your ability to drive a motor vehicle. You shouldn’t be behind the wheel if you’re impaired by any substance. That’s a message that I’m not sure is currently clearly conveyed.”

Indeed, IIHS found that drivers are largely unaware of the risks of using marijuana while driving. “There is lack of understanding about impairment risk, or impairment and driving risk, with respect to marijuana,” Harkey said. Additionally, marijuana-impaired drivers are more likely to have children in the car and are more likely to be driving during the day than alcohol-impaired drivers.

Another issue is the complexity of how THC, the psychoactive component of cannabis, affects driving impairment. “Impaired driving remains a major factor in the number of motor vehicle crashes on our roads,” says Jennifer Stockburger, director of operations at Consumer Reports’ Auto Test Center. “But with marijuana, unlike alcohol, the level of driver impairment is difficult to evaluate.” 

Unlike alcohol, the presence of THC in the body does not necessarily mean that an individual is impaired, and a higher level of marijuana use does not necessarily mean greater impairment. Different forms of THC-containing products affect the body in different ways. That makes it more difficult for researchers and law enforcement alike to determine impairment levels. Marijuana-impaired drivers are more likely to be impaired by alcohol as well, which further complicates efforts to study the problem.

“We’re going to need more research and more help from the medical community, from medical researchers, to help us understand different products with different levels of THC, how different individuals are affected by that, how that relates to impairment, and ultimately how that relates to the ability to drive a vehicle and a potential crash risk,” Harkey said.

A growing number of states are allowing some form of marijuana use. In addition to the states involved in the study, five states allow recreational use of marijuana in addition to medical marijuana, more than 20 states allow medical marijuana, and more than a dozen states allow the use of certain cannabis products for medical use. Legalization initiatives are currently pending in multiple states, and Canada became the second country to legalize recreational marijuana earlier this week. U.S. federal law still considers marijuana illegal to possess, use, or sell. 

Cannabis Laws by State

Conceding that the “ship may have sailed” when it comes to legalization, Harkey said that road-safety advocates must now work with the marijuana industry in addition to the medical community, public-health researchers, and law enforcement to reduce the number of crashes related to impaired driving.

“Are there ways we can work with the marijuana industry to try and educate the consumers and educate the public? I think these are questions for public health agencies to help us figure out,” Harkey said. He also suggested using additional tax revenue derived from marijuana sales to fund road-safety initiatives.

IIHS and HLDI also released a study of police-reported crashes in the same states that suggests similar findings.

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