Researchers at Washington State University are developing a breath test for THC, the psychoactive ingredient in marijuana. The test could be used to determine if a person is driving under the influence of marijuana, according to The Seattle Times.

Drug-impaired driving has become an increasing concern since recreational marijuana use became legal in Washington in 2012. The Washington State Toxicology Laboratory reported 25 percent of tested blood samples taken from suspected impaired drivers tested positive for active THC in 2013, compared with 18.6 percent in 2012.

Currently there is no portable tool that allows law enforcement officers to test drivers for marijuana impairment using a breath sample, the article notes. Officers now use blood tests to determine how much THC is present in a driver’s blood. Test results are not immediately available.

The new marijuana breath test is being developed by Washington State University chemistry professor Herbert Hill. He says current technologies, such as those used by airport security and customs agents to detect drugs and explosives, can be re-purposed to test for marijuana.

Washington state set the legal limit for THC at which a driver is determined to be impaired at 5 nanograms per milliliter of blood. While the breath test is unlikely to pinpoint the exact level of THC in the body, it will indicate whether some active THC is present, according to Hill. “We believe at least initially that it would lower the false positives that an officer would have,” he said. “They would have a higher level of confidence in making an arrest.”

Follow-up test results would still be needed as evidence, Hill noted. He plans to finish lab tests on the device this year, and hopes to start testing human breath in early 2015. He then plans to test the device in the field.