Field Sobriety Tests: Standardized FST

Field Sobriety Tests: What You Need to Know

Field Sobriety Tests (FSTs) are designed to assess a driver’s mental and physical abilities during a DUI stop. These tests, known as divided attention tests, evaluate whether a person can follow instructions and perform physical tasks, such as walking in a straight line or balancing on one leg. Police use FSTs to build evidence for DUI charges, but many factors—such as nervousness, fatigue, weather, or medical conditions—can affect performance and may have nothing to do with alcohol impairment.

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Field sobriety tests are voluntary, so there is no requirement that you participate in them.  The officer is generally using the Field Sobriety Tests to gather more evidence to demonstrate impairment.

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Standardized Tests

The National Highway Traffic Safety Administration (NHTSA) has designated three Field Sobriety Tests that were determined to be reliable in determining the likelihood that a person is impaired by alcohol if the tests are administered correctly, and certain clues are found.  The scientific testing occurred in 1975, but the results have been confirmed in subsequent studies.  

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1. Horizontal Gaze Nystagmus (HGN): This test measures the involuntary jerking of the eyes when moving side to side. Nystagmus can be exaggerated by alcohol, but it can also be triggered by other factors, including medical conditions.
2. Walk-and-Turn Test: This test requires a driver to walk in a straight line, touching the heal of the front foot to the toe of the back foot, turn, and return. Officers look for signs of imbalance or difficulty following instructions. However, many physical conditions, such as leg injuries, can cause poor performance.
3. One-Leg Stand Test: The driver must stand on one leg while counting out loud. Swaying or using arms for balance is noted as a sign of impairment. People with balance issues, older adults, or those with injuries may struggle with this test, even if they haven’t consumed alcohol.

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These tests are not foolproof and can be challenged in court, especially if the officer did not instruct the driver properly or did not properly record how the driver performed them.  

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Non-Standardized Tests

In addition to the standardized tests, officers may use non-standardized tests, such as the finger-to-nose test or alphabet recitation, which are not validated by the NHTSA. Because these tests lack uniform standards, they are more easily disputed in court.

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Defending FST Results

While prosecutors use FST results as evidence of impairment, a skilled DUI lawyer can challenge their accuracy. Medical conditions, anxiety, or environmental factors (such as uneven surfaces and weather) can all affect performance. Additionally, FSTs are designed to detect physical impairment, but mental impairment typically occurs first with alcohol consumption. If a driver shows no signs of mental impairment, the physical results can often be attributed to non-alcohol-related causes.

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In DUI cases, your defense attorney will investigate whether the tests were administered correctly and look for alternative explanations for any poor performance, creating reasonable doubt about the results.