Drugged driving was associated with more deaths in 2015 than driving while intoxicated, a report released by the Governors Highway Safety Association and the Foundation for Advancing Alcohol Responsibility discovered.
Of those tested, 43 percent of motorists had drugs in their system compared to the roughly 37 percent of those who tested positive for alcohol.
James Hedlund, an independent safety expert with Highway Safety North in Ithaca, New York, spoke to CNN about shifting behavior.
"Data in the report showed that for the first time, there are more dead drivers for which we have test results that are positive for drugs than there are who were positive for alcohol," he said.
While the laws governing driving while intoxicated are pretty straightforward -- it's illegal in all 50 states--that's not entirely the case when it comes to the definition of drug impairment. To make things more complicated, there is no standardization of testing practices across lines, and there are no uniform laws determining how often testing is used and what drugs are screened.
"Drug impairment is a complicated topic," Hedlund said. "Drugs can affect people in different ways. Some things make you super excited, and some things slow you down."
Nearly 400 drugs are tracked by the National Highway Traffic Safety Administration, though, marijuana accounted for 35 percent of positive tests reported. That overshadows amphetamines, which accounted for nine percent of substances detected.