Close to two-thirds of the drivers who were killed in highway crashes and tested for drugs afterward had opioids, marijuana or some combination of the two in their bodies, according to a new report on driving drugged in the United States.

That number is likely to increase as more states move to effectively legalize marijuana while struggling to find ways to detect its active use in motorists.

With legislation to legalize recreational marijuana pending in 21 states, the new Governors Highway Safety Association report urges states to move faster toward developing reliable roadside testing devices and providing better training for law enforcement to detect drivers under the influence of such drugs. That’s because studies and federal crash data suggest that more people are getting behind the wheel after getting high. In 2006, for example, nearly 28 percent of drivers who were tested for drugs also tested positive; that number increased to 43.6 percent in 2016.

Thursday’s report, using a February 2018 survey and other data, acknowledges that the science on whether legalizing marijuana has contributed to higher crash rates — or even significantly impairs one’s ability to drive — is not settled.

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Tests that detect marijuana’s active ingredient, THC, don’t always do so in a way that reflects whether a person is impaired, as traces of THC can remain in the system long after use and individual tolerance varies widely. But the group says it is reasonably certain to believe that marijuana has contributed to the causes of some crashes and increased the risk of driving for some motorists.

In addition to speedier development of new roadside tests, such as those that use saliva or sweat from a driver’s fingertips, the group call for better research on the issue. For example, testing of fatally injured drivers varies widely by state, with some conducting toxicology tests on only 2 percent of those killed in such crashes.

The report comes as nine states and the District of Columbia have legalized recreational marijuana, while 29 states and the District have allowed the use of marijuana for medical purposes. Opioid addiction has been deemed a national crisis, with an average of 115 deaths a day.

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