Coming Soon to a Police Stop Near You: Roadside THC Tests

| Dec 7, 2019 |

Researchers at the University of Texas at Dallas have developed a saliva test which determines the level of marijuana in a person’s system.

A person gives a small saliva sample, and the test administrator places that sample on a THC sensor. Then, “within 30 seconds, within a minute – it’ll tell you what the number is,” said Dr. Shalini Prasad. Over the past year, the DPS has used blood tests to confirm THC presence in about two thousand drivers. But these tests require hospital trips.

Forty-six states, including Texas, have some form of legal marijuana.

Establishing Marijuana Impairment

Currently, blood tests are basically the only available chemical tests for marijuana impairment. These tests are expensive and require search warrants. So, they are not performed very often.

Therefore, in DWI-marijuana cases, Parker County prosecutors generally rely on circumstantial evidence from the field sobriety tests, which are:

  • Horizontal Gaze Nystagmus: There is a link between marijuana use and nystagmus, or lazy eye, but it is rather tenuous. Furthermore, this controlled scientific test often takes place under uncontrolled conditions.

  • One-Leg Stand: The OLS, on the other hand, is a divided attention test specifically designed for drug impairment. During this test, officers look for intoxication clues like failing to follow directions and using arms to maintain balance.

  • Heel to Toe Walk: This test is also a divided attention test which measures mental acuity and physical dexterity. Much like the HGN test, the HTW sometimes takes place under questionable conditions. It’s almost impossible to walk an imaginary line heel to toe in the dark.

Additionally, the state must prove that the defendant failed the FSTs because the defendant was stones, and not because s/he was sleepy, nervous, or injured. To convince jurors that the defendant really was on drugs, prosecutors often use DREs, or Drug Recognition Experts, in these situations.

Despite their high-sounding title, Drug Recognition “Experts” are normally just patrol officers who attended a few training seminars. Moreover, officers usually summon DREs to the scene to confirm a drugged driving diagnosis. Their work is a self-fulfilling prophecy.

Non-Court Advocacy

Because of these weaknesses, a reliable chemical test could double the conviction rate in DWI-marijuana cases. But before such a test hits the streets, it must first go through the legislative process.

Current law defines marijuana impairment as five nanograms of THC. That’s essentially a trace amount of marijuana. A trace amount of alcohol might be impairing, but marijuana normally does not work that way.

Most alcohol users must consume three or four drinks before they become intoxicated, and that feeling may last several hours. But marijuana users experience an incredible high incredibly quickly, and the high quickly drops off to almost nothing. So, if a defendant has a few hits at a party and drives home several hours later, that person is probably not impaired.

Before approving marijuana chemical tests, the Legislature will probably hold hearings on the matter. We speak up for you in these forums.

THC tests may change the face of DWI-drug prosecutions. For a free consultation with an experienced criminal defense attorney in Weatherford, contact Herreth Law. We routinely handle matters in Parker County and nearby jurisdictions.