Legal Pot and Colorado Crash Rates: Two Studies, Two Different Conclusions

Only days after the release of a study saying that collision claim frequencies in Colorado are about 3 percent higher overall than would have been expected without marijuana legalization comes a competing report stating that the crash fatality rates haven't changed significantly. These seemingly contradictory findings leave one marijuana reformer confused but certain that the sky isn't falling.

"What is clear from both studies is that marijuana legalization has not resulted in the immediate doomsday scenario that was predicted," says Mason Tvert, one of the main proponents for Amendment 64, the 2012 measure that legalized limited recreational cannabis sales in Colorado, as well as the spokesperson for the Marijuana Policy Project.

The debate over whether marijuana legalization has led to more mayhem on Colorado highways has been raging for years. Note a 2014 analysis by the Rocky Mountain High Intensity Drug Trafficking Area, an anti-pot law enforcement group, which claimed that marijuana-impaired driving fatalities rose 100 percent in five years — an assertion ripped by critics because the study wasn't scientific, as even the RMHIDTA acknowledged.

In the case of the two new reports, however, both were produced by credible organizations. The one maintaining that collisions are up comes from the Highway Loss Data Institute, while the other offering appears in the latest edition of the American Journal of Public Health.

For its study, as noted in a summary post, the HLDI "conducted a combined analysis using neighboring states as additional controls to examine the collision claims experience of Colorado, Oregon and Washington before and after law changes. Control states included Idaho, Montana, Nevada, Utah and Wyoming, plus Colorado, Oregon and Washington prior to legalization of recreational use. During the study period, Nevada and Montana permitted medical use of marijuana, Wyoming and Utah allowed only limited use for medical purposes, and Idaho didn't permit any use."

The findings showed that "Colorado saw the biggest estimated increase in claim frequency compared with its control states. After retail marijuana sales began in Colorado, the increase in collision claim frequency was 14 percent higher than in nearby Nebraska, Utah and Wyoming."

This last figure is an average, and there were state-to-state variations. For instance, Colorado's collision claim frequency varied from "a 3 percent rise in claim frequency when compared with Wyoming to a 21 percent increase when compared with Utah," the summary points out.

These results received lots of play locally and nationally, even though a Colorado State Patrol spokesperson was quoted as saying his agency had actually seen a decrease in driving-impaired accidents since legal recreational marijuana sales began. As for Tvert, he finds a lot about the study to be flat-out baffling. "I haven't found a reporter covering this who can explain why the study makes sense," he says, noting that "they factored in things like the average temperatures and employment rates — and they didn't actually look at the cause of the accidents to see if marijuana was involved. It's very complex and difficult to really figure out what they're looking at."

The American Journal of Public Health study "Crash Fatality Rates After Recreational Marijuana Legalization in Washington and Colorado," by Jayson D. Aydelotte (MD), Lawrence H. Brown (PhD), Kevin M. Luftman (MD), Alexandra L. Mardock (BA), Pedro G.R. Teixeira (MD), Ben Coopwood (MD) and Carlos V.R. Brown (MD), is much more straightforward.

In it, an extract explains, "researchers evaluated motor vehicle crash fatality rates in the first two states with recreational marijuana legalization and compared them with motor vehicle crash fatality rates in similar states without recreational marijuana legalization. Using the U.S. Fatality Analysis Reporting System, they determined the annual numbers of motor vehicle crash fatalities between 2009-2015 in Washington, Colorado and eight control states."

The results: "Pre–recreational marijuana legalization annual changes in motor vehicle crash fatality rates for Washington and Colorado were similar to those for the control states. Post–recreational marijuana legalization changes in motor vehicle crash fatality rates for Washington and Colorado also did not significantly differ from those for the control states."

The studies took distinct angles on marijuana and driving, and it's possible that fender benders in Colorado have gone up since pot was legalized even as fatalities stayed flat. Still, the outcomes of these studies seem so far apart from one another that the only thing Tvert knows for sure is that "further study is warranted."

Click to read the Highway Loss Data Institute report and access the American Journal of Public Health effort.