A field sobriety test in Arizona measures specific physical and cognitive functions. It doesn’t measure general clumsiness. Officers use a standardized battery developed by the National Highway Traffic Safety Administration, and each test targets a different sign of impairment. Knowing what each one actually looks for makes the whole roadside process far less mysterious.
The three standardized field sobriety tests Arizona officers use
NHTSA validated three tests through decades of research. Arizona officers train on the same standardized battery used nationwide. Each test isolates a different function that alcohol impairs.
Field sobriety test one: horizontal gaze nystagmus (HGN)
The officer moves a small object, usually a pen or flashlight, side to side. They watch the driver’s eyes track it. Alcohol causes an involuntary jerking of the eyes — nystagmus — that becomes more pronounced and appears earlier in the range of motion as BAC rises. This test measures an involuntary physiological response. That’s part of why it’s weighted heavily in officer training. Its accuracy still depends heavily on the officer administering it correctly.
Field sobriety test two: walk-and-turn
The driver takes nine heel-to-toe steps along a straight line, turns, and returns. This test measures divided attention: the ability to listen to instructions, remember them, and perform a physical task at the same time. Officers watch for specific clues. Stepping off the line, using arms for balance, an improper turn, and starting before instructed all count.
Field sobriety test three: one-leg stand
The driver stands on one foot with the other raised about six inches off the ground. They count aloud for 30 seconds. Like the walk-and-turn, this measures divided attention and balance together. Swaying, hopping, and putting the foot down are all scored clues.
What a field sobriety test actually measures
None of these three tests measure blood alcohol concentration directly. They measure functions instead: eye tracking, balance, and the ability to divide attention between physical and mental tasks. That’s an important distinction. Factors unrelated to alcohol can affect performance on these tests too. Fatigue, certain medical conditions, inappropriate footwear, uneven pavement, and simple nervousness during a roadside stop can all play a role.
Is a field sobriety test mandatory in Arizona?
No. Field sobriety tests are voluntary under Arizona law. That’s different from the chemical breath, blood, or urine test governed by the state’s implied consent law. A driver can decline to perform them without facing an automatic license suspension the way a chemical test refusal triggers. Declining doesn’t prevent an arrest by itself. An officer can still develop probable cause through other observations made during the stop.
How field sobriety test results get used afterward
An officer’s notes on performance — which clues were observed on each test — typically become part of the police report. They can support probable cause for arrest. In some cases, stops are also recorded on body-worn or dash cameras, giving both sides a record beyond the officer’s written account. How reliable a specific administration of these tests was is a fact question. It depends on the officer’s training, the conditions at the scene, and the footage available.
The bottom line
A field sobriety test in Arizona is built from three specific, standardized components: eye movement, walking balance, and standing balance under divided attention. They’re voluntary. They don’t measure BAC directly, and outside factors can affect performance on them. What weight a particular result carries in a particular case depends on how it was administered and what else the officer observed during the stop.
Frequently asked questions
The horizontal gaze nystagmus test, the walk-and-turn, and the one-leg stand. NHTSA developed and validated all three, and Arizona officers train on the same standardized battery.
No. They’re voluntary, unlike the chemical breath, blood, or urine test covered separately under Arizona’s implied consent law.
Yes. Fatigue, certain medical conditions, inappropriate footwear, uneven pavement, and nervousness can all affect performance on these tests independent of alcohol.
No. They measure functions like eye tracking, balance, and divided attention, not BAC directly. A separate chemical test measures BAC itself.
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This article explains what Arizona’s standardized field sobriety tests are designed to measure. It does not evaluate the reliability of any specific test administration, which depends on the officer’s training and the conditions at the scene.