A traffic safety organization says drugs have become a considerably more prominent source of impairment in the past decade, as drivers killed in crashes are more likely to test positive for drugs than alcohol.

The Governors Highway Safety Association, which represents state highway safety organizations and aims to eliminate traffic fatalities, recently issued a report entitled "Drug-Impaired Driving: Marijuana and Opioids Raise Critical Issues for States." Researchers determined that 43.6 percent of drivers who were fatally injured in crashes in 2016 tested positive for drugs, up from 27.8 percent in 2006.

Thirty-eight percent of those who tested positive for drugs had marijuana in their system, while 16 percent tested positive for opioids. Four percent tested positive for both.

"Drugs can impair, and drug-impaired drivers can crash. But it's impossible to understand the full scope of the drugged driving problem because many drivers who are arrested or involved in crashes, even those who are killed, are not tested for drugs," said Jim Hedlund, author of the report. "Drivers who are drug-positive may not necessarily be impaired."

Alcohol was less prevalent among drivers killed in crashes in 2016. A total of 37.9 percent tested positive for alcohol, down from 41 percent in 2006.

More than half of fatally injured drivers who tested positive for drugs—51 percent—were found to be using two or more drugs prior to the crash. Forty-nine percent of those who tested positive for alcohol also tested positive for drugs.

"Alcohol-impaired driving and drug-impaired driving can no longer be treated as separate issues," said Ralph Blackman, president and CEO of the Foundation for Advancing Alcohol Responsibility, which funded the research. "Drunk driving, which was involved in 28 percent of 2016 traffic fatalities, remains a critical issue; however, to curb impaired driving, we have to think about the combination of substances drivers are often putting into their systems at the same time."

The GHSA said some of the same strategies used to deter driving under the influence of alcohol could also be used to combat drugged driving. These include training law enforcement officers to identify drivers who are potentially under the influence of drugs, public awareness campaigns, and working with health organizations and others to educate drivers about the effects of various drugs on their ability to drive a vehicle.

"Too many people operate under the false belief that marijuana or opioids don't impair their ability to drive, or even that these drugs make them safer drivers," said Jonathan Adkins, executive director of the GHSA. "Busting this myth requires states to expand their impaired driving campaigns to include marijuana and opioids along with alcohol to show drivers that impairment is impairment, regardless of substance."

However, the organization also noted that drugged driving presents its own set of challenges. Unlike the blood-alcohol test for drunk driving, there is no nationally accepted test for drug impairment. There are also an "unwieldy number" of potentially impairing drugs that such a test would have to identify, and the effects of drug impairment vary from driver to driver.

The GHSA report advocates for the continued effort to develop devices to test impaired drivers for drug use, such as breath tests to determine if a driver recently used marijuana. It also calls for the establishment of a separate driving under the influence of drugs offense, equivalent to the driving under the influence of alcohol penalty; penalties for drivers who refuse to take a drug test if suspected of impairment; blood testing for drugs rather than urine testing; and drug tests for all drivers involved in fatal crashes to determine if they were under the influence of drugs or alcohol.