Crashes are up by as much as six percent in Colorado, Nevada, Oregon and Washington, compared with neighboring states that have not yet legalized marijuana for recreational use, according to research from the Insurance Institute for Highway Safety (IIHS) and Highway Loss Data Institute (HLDI).
Colorado and Washington were the first states to legalize recreational marijuana for adults 21 and older with voter approval in November 2012. Retail sales began in January 2014 in Colorado and in July 2014 in Washington. Oregon voters approved legalized recreational marijuana in November 2014, and sales started in October 2015. Nevada voters approved recreational marijuana in November 2016, and retail sales began in July 2017.
HLDI analysts estimate that the frequency of collision claims per insured vehicle year rose a combined 6 percent following the start of retail sales of recreational marijuana in Colorado, Nevada, Oregon and Washington, compared with the control states of Idaho, Montana, Utah and Wyoming.
The combined-state analysis was based on collision loss data from January 2012 through October 2017. Analysts controlled for differences in the rated driver population, insured vehicle fleet, the mix of urban versus rural exposure, unemployment, weather and seasonality.
Collision claims are the most frequent kind of claims insurers receive. Collision coverage insures against physical damage to a driver’s vehicle in a crash with an object or other vehicle, generally when the driver is at fault. Claim frequencies are expressed as the number of claims per 100 insured vehicle years. An insured vehicle year is one vehicle insured for one year or two vehicles insured for six months each.
A separate IIHS study examined 2012–16 police-reported crashes before and after retail sales began in Colorado, Oregon and Washington. IIHS estimates that the three states combined saw a 5.2 percent increase in the rate of crashes per million vehicle registrations, compared with neighboring states that didn’t legalize marijuana sales.
“The new IIHS-HLDI research on marijuana and crashes indicates that legalizing marijuana for all uses is having a negative impact on the safety of our roads,” said IIHS-HLDI President David Harkey. “States exploring legalizing marijuana should consider this effect on highway safety.”
Marijuana is still an illegal controlled substance under federal law.
In addition to the study states, Alaska, California, Maine, Massachusetts, Vermont and the District of Columbia also allow recreational use of marijuana for adults 21 and older and medical use of marijuana. Another 22 states allow medical marijuana, while 15 more states permit the use of specific cannabis products for designated medical conditions.
New Hampshire, New Jersey, New York and Pennsylvania are weighing legalization of recreational use.
This past November, voters in Michigan approved legalizing recreational marijuana while Missouri and Utah joined states in approving medical marijuana.
Driving under the influence of marijuana is illegal in all 50 states and D.C., but determining impairment is challenging. Unlike alcohol, the amount of marijuana present in a person’s body doesn’t consistently relate to impairment. THC, or Tetrahydrocannabinol, is the primary psychoactive component of cannabis. A positive test for THC and its active metabolite doesn’t mean the driver was impaired at the time of the crash. Habitual users of marijuana may have positive blood tests for THC days or weeks after using the drug.
The researchers note that marijuana’s role in crashes isn’t as clear as the link between alcohol and crashes. Many states don’t include consistent information on driver drug use in crash reports, and policies and procedures for drug testing are inconsistent. More drivers in crashes are tested for alcohol than for drugs. When drivers are tested, other drugs are often found in combination with alcohol, which makes it difficult to isolate their separate effects.
“Despite the difficulty of isolating the specific effects of marijuana impairment on crash risk, the evidence is growing that legalizing its use increases crashes,” Harkey said.