What is a Field Sobriety Test?
Standard field sobriety tests were developed years ago by the NHTSA (National Highway Traffic Safety Administration) to detect impairment among drivers on the roadways. There are three standard FSTs officers may use to establish probable cause for arrest:
One-Leg Stand. This test has the subject stand on one leg with the other leg approximately 6 inches from the ground, for about half a minute. The test is designed to detect balance problems. Those problems may reveal themselves in swaying, needing your arms to balance, and other indicators.
Walk and Turn. This test requires that you walk a specified number of steps in a particular way, then turn 180° and walk back in the other direction. The test measures not only your ability to walk a line without staggering, but also your ability to follow directions while performing the test.
HGN. Horizontal Gaze Nystagmus (HGN) is an involuntary eye movement that is exaggerated in those who are intoxicated. HGN is measured by asking you to track a light held by the officer.
Are Field Sobriety Tests (FSTs) Mandatory in Arizona?
Under Arizona law, you are not legally required to perform field sobriety tests, however, declining these roadside tests may still result in arrest. Also, a prosecutor may use your refusal as evidence of impairment in court.
How Reliable Are These Tests?
These tests are highly subjective and can be influenced by many non-alcohol-related factors. Research shows walk-and-turn accuracy is around 68%, and one-leg-stand about 65%—even in controlled conditions. Conditions like uneven ground, poor lighting, nervousness, age, injury, or medical conditions can cause failures even if you’re sober.
When It’s Time to Call a DUI Defense Lawyer
Seek representation quickly—FST refusal and related evidence will play a major role in your case strategy.