Although Colorado and Washington allow recreational marijuana use, a driver in either state can be charged with driving under the influence (DUI) if he or she has five nanograms or more of THC (i.e., tetrahydrocannabinol, the active ingredient in marijuana) in his or her blood (COLO. REV. STAT. § 42-4-1301 and WASH. REV. CODE § 46.61.506).
According to a recent USA Today article, police in both states rely on blood tests to determine whether someone has been smoking marijuana or consuming it. Washington State University researchers are developing a marijuana breath test that police could use when deciding whether to arrest a suspected impaired driver. Because the breath test will not be able to pinpoint the level of THC in the body, follow-up tests would still be needed for evidentiary purposes, as with drunken driving cases.
The Washington State University research team plans to finish testing a prototype marijuana breath test by the end of this year and begin human testing in 2015, per the article.
According to a previous USA Today article, the federal government has recently completed an experiment aimed at identifying the level of marijuana that impairs drivers.
