Competing studies leave haze of uncertainty connecting marijuana to traffic accidents

Author: Peter Marcus - July 3, 2017 - Updated: July 3, 2017

In this Friday, Dec.18, 2015, file photograph, the logo is shown on the front of jars of marijuana buds marketed by rapper Snopp Dogg in one of the LivWell marijuana chain's outlets south of downtown Denver. As legal marijuana becomes a further-entrenched fact of life in Colorado, small-town leaders are struggling to sort out the same issues that Denver and other cities have tangled with, from zoning for grows and dispensaries to allowing cannabis clubs. (AP Photo/David Zalubowski, file)
(AP Photo/David Zalubowski, file)

Two competing studies attempting to draw a connection between marijuana legalization and car crashes have created even greater uncertainty on the subject.

The Insurance Institute for Highway Safety released a report on June 22 stating that marijuana legalization in Colorado, Oregon and Washington resulted in collision claim frequencies that are about 3 percent higher than would have been expected without legalization.

The IIHS’s Highway Loss Data Institute report points out that researchers haven’t been able to definitively connect cannabis use with more frequent real-world crashes.

The study looked at insurance claims for vehicle collisions between 2012 and 2016. Colorado legalized recreational marijuana in 2012, which took effect on Jan. 1, 2014. Claims were compared to neighboring states without legal marijuana.

Meanwhile, a second study also published online on June 22 in the American Journal of Public Health found no increase in traffic fatalities in Colorado and Washington after legalization.

Researchers used the U.S. Fatality Analysis Reporting System to determine the annual numbers of vehicle crash fatalities between 2009 and 2015 in Washington, Colorado and eight comparable states. The study compared changes in fatality rates before and after legalization.

The study found that post-legalization changes in fatality rates for Washington and Colorado did not significantly differ from those for the comparable states.

The study also found no association between recreational marijuana legalization and total crash rates when analyzing available state-reported nonfatal crash statistics.

“Three years after recreational marijuana legalization, changes in motor vehicle crash fatality rates for Washington and Colorado were not statistically different from those in similar states without recreational marijuana legalization,” the study found.

Mason Tvert, spokesman for the pro-legalization Marijuana Policy Project, said the two studies indicate that there are no strong conclusions that can be drawn.

“This area of research is characterized by confounding factors and limited data, so it is not particularly surprising to see different research methods arriving at different results,” Tvert said. “What is clear from both studies is that Colorado’s decision to regulate marijuana for adult use has not resulted in the instant doomsday scenario that some had predicted. This is an important issue deserving of study, and it will surely continue to be examined.”

Peter Marcus

Peter Marcus

Peter Marcus is senior statehouse reporter for Colorado Politics. He covers the legislature and previously covered politics, the governor’s office, the legislature and Congress for The Durango Herald. He joined The Herald in 2014 from The Colorado Statesman, a Denver-based political weekly. The Washington Post twice named Marcus one of the nation’s top state-based political and legislative reporters.