The number of Colorado drivers who have tested positive for marijuana use after a fatal crash has more than doubled since 2013, according to a new analysis published by the Denver Post.

The newspaper studied federal and state crash data as well as county coroner reports since 2013. The shifting trend in fatal-crash drug test results seems to correspond with the state’s legalization of recreational marijuana use. In November 2012, Colorado voters approved a ballot measure that made recreational marijuana legal for adults 21 and older. Retail sales began in January 2014.

The Post analysis does come with a noteworthy caveat: Positive test results for marijuana don’t conclusively prove that the driver was high at the time of the crash. Someone can test positive for the drug days or even weeks after using it.

Nonetheless, the numbers are eye-opening.

From 2013 to 2016, the state saw a 40% jump in the number of all drivers involved in fatal crashes — from 627 to 880, the Post reported. From 2013 through 2015 (2016 data aren’t yet available), the number of drivers who tested positive for alcohol after a fatal crash rose 17% — from 129 to 151. But the number of drivers testing positive for marijuana after a fatal crash leaped 145% — from 47 in 2013 to 115 in 2016.

In 2013, drivers in fatal crashes tested positive for marijuana about 10% of the time, the Post reported. But by 2016, that figure rose to 20%. In 2015, the average age of drivers testing positive following a deadly crash was nearly 35 years old.

In 2015, Colorado had 547 road deaths. A total of 99 of these fatalities involved drivers who tested positive for marijuana, the newspaper reported, and 187 involved drivers who tested positive for alcohol. Of those, 35 road deaths involved drivers who tested positive for both alcohol and marijuana.

Despite the dramatic change in test result trends, the prevalence of driver drug testing didn’t change in any appreciable way during that same period, federal crash data indicated.

What’s more, some drivers didn’t test positive simply because they weren’t drug-tested at all. Not all coroners drug-test deceased drivers for marijuana use; it’s not required by law. And some police agencies don’t bother drug-testing a surviving driver if he or she has a blood alcohol concentration of more than .08% and can be charged with driving under the influence anyway.