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Field Sobriety Tests

The roadside balance, coordination and eye-movement exercises an officer uses to build probable cause for an impaired-driving arrest - usually voluntary, and never the same thing as the chemical test that follows.

Informational only - this is not legal advice. These definitions explain general legal vocabulary in plain English. They are not advice about your situation, reading them creates no attorney-client relationship, and the law differs from state to state and changes over time. For advice you can rely on, speak to a lawyer licensed in your state.

What it means

Field sobriety tests are the physical exercises an officer asks a driver to perform at the roadside during a suspected impaired-driving stop. The standardised battery used across the United States has three parts: an eye-movement test in which the officer watches for involuntary jerking as the eyes track a moving object, a walk-and-turn along a line, and a one-leg stand. The officer scores "clues" - a missed heel-to-toe step, using the arms for balance, starting too soon - and the total is what the officer relies on, together with driving behaviour, speech and odour, to decide whether there is probable cause to arrest.

The tests are not a measurement of alcohol. They are a screening tool with a documented error rate, developed to correlate with a blood-alcohol level, and they are affected by age, weight, injuries, footwear, the road surface, the weather and nervousness. That is why, in most states, a driver may decline them: unlike the chemical test after arrest, the roadside exercises are generally not covered by the implied-consent law, and refusing them usually carries no administrative penalty - though the refusal may be described to a jury, and the officer can still arrest on the other evidence. A preliminary breath test at the roadside is a different instrument with its own state rules.

At trial the tests are attacked on how they were given as much as on the result. The standardised battery has prescribed instructions and scoring, and an officer who deviated from them, or who administered a non-standardised exercise such as reciting the alphabet or touching the nose, has produced evidence that a court may limit or exclude. The dashboard or body-camera recording is usually the most important exhibit.

Where this comes from

The standardised battery and its administration and scoring are set out in the National Highway Traffic Safety Administration's DWI Detection and Standardized Field Sobriety Testing curriculum, a training standard rather than a statute. Whether a driver may refuse the roadside tests without penalty, whether a refusal is admissible, and what weight the results carry are matters of state statute and case law and differ by state. The implied-consent rules that govern the chemical test after arrest are a separate body of law and are covered under that entry.

When people hire a lawyer for this

The decision at the roadside is made without a lawyer, which is why it is worth knowing the general rule in your state beforehand. Afterwards, a lawyer's first request is the recording, and the case often turns on whether the exercises were administered and scored the way the standard requires rather than on how the driver performed them.

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Part of the LawyerLand plain-English legal glossary. Definitions are written from primary sources - statutes and court rules - and each entry states the authority it rests on, or says plainly when the doctrine is state law with no national rule.

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