How Do Marijuana DUI Field Sobriety Tests Work in Washington?

Washington has legalized recreational marijuana, and police now arrest and convict far more drivers for marijuana DUI than in the past. Deciding whether to arrest a driver for marijuana impairment can be difficult for officers. Unlike with an alcohol-related DUI, there are very few roadside tools that reliably and accurately detect marijuana impairment. To decide whether to arrest, officers often rely on field sobriety tests and their own observations. Marijuana DUI field sobriety tests are not always accurate, and the Tacoma marijuana DUI lawyers at Smith & White may be able to challenge these results and ask the court to suppress them.

Marijuana DUI Field Sobriety Tests

Researchers and companies continue to develop tools to test for marijuana use. However, tools currently on the market often take days to process and still cannot show when, or how recently, a driver used marijuana. You may have THC in your bloodstream even if you last used weeks ago. Until more accurate and timely tests exist, officers rely mainly on observations and field sobriety tests to decide whether somebody appears impaired by marijuana.

The National Highway Traffic Safety Administration (NHTSA) has standardized three field sobriety tests: the walk and turn, the one leg stand, and the horizontal gaze nystagmus. NHTSA designed and validated these tests for drunk driving investigations, not marijuana DUI cases. Alcohol affects the body in different ways than marijuana. Because of that, the same clues that suggest alcohol impairment do not always match a person’s actual level of THC impairment. Medical conditions, fatigue, age, footwear, and road conditions can all affect how a person performs, even when they are sober.

Drug Recognition Experts in Marijuana DUI Cases

Some officers receive extra training as Drug Recognition Experts (DREs). An arresting officer with DRE training may ask a driver to submit to a full evaluation. If the officer completes all required steps and the prosecutor lays the proper foundation in court, the State may present that officer as an expert witness.

DREs must log every evaluation they perform. Those logs should show how often the officer correctly identifies the type of drug involved, based on later blood analysis. A defense attorney can compare these logs to the toxicology results to see how accurate the officer’s opinions have actually been.

Officers often give field sobriety tests along with the DRE evaluation. Prosecutors may offer these tests as evidence in court, but a Tacoma DUI defense attorney can challenge them in several ways, such as:

Arguing that the officer did not follow NHTSA instructions or scoring rules.
Pointing to medical, vision, or balance issues that affected performance.
Showing that road, lighting, or weather conditions made the tests unfair.
Arguing that the officer obtained the tests or statements in violation of your constitutional rights.

Horizontal Gaze Nystagmus Test

When an officer gives the horizontal gaze nystagmus test, they move an object or a finger from side to side in front of the driver’s face. They watch for involuntary jerking of the eyes, which NHTSA links to significant alcohol intoxication. Your eyes may jerk back and forth if they are strained at more than a 45-degree angle when you are under the influence. In controlled alcohol studies, NHTSA has reported that this type of field sobriety test is about 77% reliable.

Marijuana does not consistently produce the same eye-movement patterns as alcohol. Because of this, most experts do not view the horizontal gaze nystagmus test as a reliable way to measure cannabis impairment. An attorney can argue that HGN deserves little or no weight in a marijuana DUI case and can compare the officer’s description to any body camera or dash camera video.

Walk and Turn Test

The walk and turn test divides your attention between physical coordination and mental focus. The officer explains the test and then watches to see whether you:

Walk an incorrect number of steps.
Step off the line or lose your balance.
Start before you are instructed to begin.

NHTSA has estimated that the test is effective about 68% of the time for alcohol. That estimate comes from studies that took place under controlled conditions. Uneven pavement, poor lighting, nervousness, footwear, age, or injuries can all affect your performance. As a result, a driver can “fail” the walk and turn even when not impaired, especially when marijuana rather than alcohol is involved.

One Leg Stand Test

During a one leg stand, a police officer tells you to lift one foot, stay still, count, and look down at your raised foot. The officer may conclude that you are under the influence if you hop, put your foot down, sway, or use your arms for balance. NHTSA has estimated that the test is reliable about 65% of the time for alcohol. Of the three primary field sobriety tests, this test is considered the least reliable for alcohol cases.

For marijuana cases, the one leg stand can be even less dependable. Drivers with back, knee, ankle, or balance problems—or drivers who are older, tired, or standing on a sloped or rough surface—may struggle with this test even when completely sober. A skilled attorney can use those facts to argue that poor performance on the one leg stand does not prove marijuana impairment.

Consult an Experienced Tacoma Attorney

Our attorneys can review the circumstances of your case to determine whether irregularities in your marijuana DUI field sobriety tests give you grounds to file a motion to suppress evidence or raise reasonable doubt at trial. If you believe that there was a problem with how your tests were given or interpreted, that issue may be a strong part of your defense. Based in Tacoma, the attorneys at The Law Offices of Smith & White, PLLC, represent drivers across Pierce, King, Kitsap, and Thurston Counties. Call us at (253) 203-1645 or contact us through our online form.