The Highway Loss Data Institute — which, like the IIHS, is a nonprofit organization backed by insurance companies — reported in June that insurance companies received higher-than-expected collision claims in Colorado, Washington and Oregon after those states allowed people to buy marijuana for recreational purposes. The frequency of claims rose about 3 percent, compared with surrounding western states that continued to have laws on the books prohibiting recreational use of marijuana, the institute found.
Meanwhile, the University of Texas study also found an increase in fatal crashes in two states that fully legalized pot. Yet the authors of the UT study — which was published in the online edition of the American Journal of Public Health in June — also said that the increase was too small to be statistically significant.
The IIHS, in its upcoming Status Report newsletter, takes a slightly different view of the Texas study than the Texas researchers did. The IIHS argues that the Texas study may have been structured in such a way as to have underestimated the effect of recreational marijuana use.
For example, UT researchers focused on a period that coincided with voters’ legalization of recreational marijuana in one of the targeted states — but before weed became widely available for purchase. The IIHS said it makes sense that a larger effect might have been seen when looking at crash rates after retail sales began.
The upshot, according to the IIHS, is that the early evidence suggests that making it easier for people to get high is also likely to make it easier for people to wreck their vehicles.
But the question is far from settled, and probably the aspect all the studies agree on is the need for more research. In December, for example, Columbia University researchers reported a reduction in traffic fatalities in states that enacted medical marijuana laws, possibly because fewer people were driving drunk.
The analysis of the two studies is included in the IIHS Status Report due for release Thursday.