Story highlights Nationwide in 2015, only 57% of fatally injured drivers were tested for drugs

Of the positive tests reported, 35% were positive for marijuana

This story has been updated to reflect more precise language on the presence of drugs found in the bodies of those involved in 2015 auto fatalities.

(CNN) Driving while on drugs was associated with more deaths in 2015 than driving with alcohol in one's system, a new report found. Still, some safety experts caution that drunken driving remains a bigger problem and say that "drugged driving," as the report refers to it, needs more research.

Positive drug tests were more common than the presence of alcohol among the fatally injured drivers who were tested in 2015, according to the report (PDF) "Drug-impaired Driving," released Wednesday by the Governors Highway Safety Association and the Foundation for Advancing Alcohol Responsibility, a nonprofit funded by alcohol distillers.

Of those tested, 43% of motorists who died had drugs in their system, the report said. This number surpassed the 37% of motorists who died who tested positive for alcohol in the same year.

"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," said James Hedlund, an independent safety expert with Highway Safety North in Ithaca, New York. The new report adds to earlier research conducted by Hedlund that addressed behavioral highway safety issues, including drug-impaired driving.

"As states across the country continue to struggle with drug-impaired driving, it's critical that we help them understand the current landscape and provide examples of best practices so they can craft the most effective countermeasures" to combat the issue of drug-impaired driving, governors association Executive Director Jonathan Adkins said.

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