Field Sobriety Tests Explained
Field sobriety tests are the roadside exercises an officer uses to gather evidence of impairment before deciding whether to arrest. There are three standardized tests, and they're different from the breath or blood test that measures your BAC. Here's what they are and how they work.
The three standardized tests
The National Highway Traffic Safety Administration recognizes three Standardized Field Sobriety Tests (SFSTs): the Horizontal Gaze Nystagmus test (following a moving object with your eyes while the officer watches for involuntary jerking), the Walk-and-Turn (nine heel-to-toe steps, a turn, and nine back), and the One-Leg Stand (standing on one foot while counting). Officers score them by looking for specific 'clues.'
What they are — and aren't
Field sobriety tests are designed to establish probable cause to arrest, not to measure your exact blood alcohol level. They're subjective, scored by the officer's observations, and can be affected by nerves, medical conditions, footwear, and road conditions. The chemical test that follows an arrest is what produces the BAC number.
Are they mandatory?
In many states field sobriety tests are voluntary and you may decline them, though declining can still factor into the officer's decision to arrest, and it is separate from the post-arrest chemical test covered by implied-consent laws. Whether and how to decline depends on your state and situation.
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Frequently asked questions
What are the three standardized field sobriety tests?
The Horizontal Gaze Nystagmus (eye-tracking) test, the Walk-and-Turn, and the One-Leg Stand. These three are the field tests standardized by the National Highway Traffic Safety Administration.
Do I have to take a field sobriety test?
In many states field sobriety tests are voluntary and can be declined, unlike the official chemical test after arrest, which is covered by implied-consent laws. Rules vary by state, and declining can still influence whether the officer arrests you.
Are field sobriety tests accurate?
They're subjective and scored on the officer's observations, and factors like anxiety, medical conditions, footwear, and uneven ground can affect performance. They're used to establish probable cause, not to measure your exact BAC.