— Marijuana enthusiasts might fancy the grass a bit greener in states with legalized recreational use, a list that now includes eight states plus the District of Columbia. But when it comes to driving safety, a new study poses doobie-ous ramifications. In an analysis published today, the Insurance Institute for Highway Safety says three states with legalized marijuana got high in one other area: collision claims.
IIHS studied the frequency of collision claims — that is, claims of damage to the driver's car, usually because of an accident the driver caused — in Colorado, Oregon and Washington. All three states have legalized recreational weed: Washington and Colorado in 2012, and Oregon in 2015. And collision claims in those states are about 3 percent higher than they would have been without legalization, IIHS says.
The agency looked at collision claims in Washington, Oregon and Colorado before and after respective legalization took place, comparing claim frequency with five neighboring states: Idaho, Montana, Nevada, Utah and Wyoming. IIHS analyzed claims from January 2012 to October 2016 in those eight states for vehicles from model years 1981 to 2017, controlling for various other factors (urban versus rural exposure, for example).
The results would harsh anyone's mellow. After Colorado legalized retail marijuana, the uptick in collision-claim frequency was 14 percent higher than in adjacent Nebraska, Utah and Wyoming. Washington's increase in claim frequency outpaced nearby Montana and Idaho by 6.2 percent, while Oregon's increase exceeded nearby Idaho, Montana and Nevada by 4.5 percent, IIHS says.
A combined analysis with a larger control group brings the increase in frequency to 3 percent. It's separate from the individual state analysis, as it takes in more data from the eight Western states — including Colorado, Oregon and Washington — to ensure "a statistically significant effect," IIHS spokesman Russ Rader told .
"As you can tell, it's not an average for the three states," Rader wrote in an email. "Using more data brought down the increase, but the key is that all the signals, no matter how we cut the claims data, point to an increase."
Indeed, the results are a "good representation of the effect of marijuana legalization overall," IIHS notes. The agency says this is its first analysis of how legalized marijuana since 2014 affects accident claims. The findings "should give other states eyeing legalization pause," said David Zuby, IIHS executive vice president and chief research officer, in a statement.
IIHS is conducting a larger study in Oregon to compare legalized marijuana with injury-producing crashes, with results expected in 2020. Still, this study is a warning flag. Past studies haven't been able to "definitively connect" marijuana usage and crashes, IIHS notes — including a 2015 government study that found inconclusive ties between pot and crashes.
In a statement today, the Governors Highway Safety Association said IIHS' research "reinforces the need for states to consider the risk of marijuana-impaired driving as they move toward liberalizing marijuana laws."