There are many reasons why it's valid to question the accuracy of the tests authorities use to determine if a person may be driving impaired. Breath tests can be wrong if administered incorrectly or if the measuring device is improperly calibrated. Field sobriety tests are often a weak basis for bringing impaired driving charges, too, because even a sober person can get tripped up by them.
As ineffective as many such tests may be in confirming drunk driving, experts say matters are worse when it comes to trying to confirm if a person has been driving under the influence of a drug.
The problem is that while there is general consensus that a 0.08 percent blood alcohol content, confirmed by blood testing, correlates to an unacceptable impairment level, no such correlation exists for the psychoactive ingredient in marijuana, THC. Blood tests have shown that a person can test positive for active levels of THC a full week after ingestion, and in the states where drug impaired driving laws are enforced, blood tests are typically the norm.
But researchers at the National Institute on Drug Abuse recently concluded that a marijuana breath test may be a viable tool for police. They made their determination by comparing exhaled breath samples from a group made up of chronic smokers who smoke four times a week or more, and a group of people who smoke two times a week or less. Each test group was breath tested after smoking a marijuana cigarette with a 6.8 percent THC level.
The researchers found that all the samples of the chronic smokers tested positive for THC, and 90 percent of the samples of the occasional smokers came back positive. They warn though that the window of opportunity for accurate detection was short -- somewhere between 30 minutes and two hours.
There is no indication from the reports we've read that any state is poised to begin allowing breath test evidence in a court of law. Considering the issues that exist with current test methods, caution about adopting something new would seem to be in order.
Source: HuffingtonPost.com, "Marijuana Breath Test Could Offer Alternative To Controversial Blood Test For Pot DUIs," Matt Ferner, Oct. 22, 2013