With the rapid expansion of legal marijuana sales in Massachusetts and more than 30 other states, it was high time someone made progress developing a device to detect THC on a person’s breath. 

Two University of Pittsburgh researchers unveiled what NPR dubbed a “weed Breathalyzer” similar to the well-known device that measures a person’s blood-alcohol content when they blow into it. The prototype of the weed device created by Ervin Sejdic and Alexander Star can measure the amount of THC — the active ingredient in marijuana that brings on the high — in a person’s breath. 

Police and prosecutors have been concerned for years about how to accurately determine whether someone is driving high on pot. There are the roadside tests and questions a police officer poses to make an assessment. But prosecutors know that measurable evidence helps convince judges and juries that a person is driving drunk, so it makes sense that finding a scientifically sound way to measure the level of a narcotic in a person’s system could serve the same purpose.

The NPR report said the device uses tiny carbon tubes to “recognize the presence of THC, even when other substances are in the breath, such as alcohol.” The report said the device is almost ready for mass production. That might be good news to law enforcers in states that have legalized marijuana in some form.

The device still needs testing, and there have to be ways to correlate a person’s THC output to that person’s level of impairment. In other words, like the debate about what percentage of alcohol in the blood is the legal benchmark to charge someone with drunken driving, experts in the medical, legal and law enforcement communities will have to find agreement on what constitutes impaired driving after one smokes or ingests pot. 

Whatever the ultimate tool to measure impaired driving, and whatever the gauge that’s employed, it’s essential that a device is created that can help society set a bar to determine who is too high to drive safely.

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