An increasing number of Washington state drivers involved in fatal crashes are testing positive for recent use of marijuana, according to new research.

A study by the AAA Foundation for Traffic Safety (AAA) found the number of drivers who, after a fatal crash, tested positive for active THC – the drug’s main psychoactive ingredient – has doubled since the state legalized marijuana in December 2012.

AAA says the increase raises important traffic safety concerns for drivers across the country, because recreational marijuana use is now legal in 11 states and Washington DC.

The latest AAA Foundation research found that between 2008 and 2012 – the five-year period before the drug was legal – an estimated 8.8 percent of Washington drivers involved in fatal crashes were positive for THC. That rose to 18 percent between 2013 and 2017.

The average number of THC-positive drivers increased, too. In the five years before legalization, an average of 56 drivers involved in fatal crashes each year were THC-positive. In the five years after legalization, the average jumped to 130.

“This study enabled us to review a full ten-years’ worth of data about the potential impact of marijuana on driving safety – and it raises significant concerns,” said Dr David Yang, Executive Director of the AAA Foundation for Traffic Safety.

“Results from the analysis suggest that legalization of recreational use of marijuana may increase the rate of THC-positive drivers involved in fatal crashes.”