The Three Standardized Field Sobriety Tests
The National Highway Traffic Safety Administration (NHTSA) has validated three Standardized Field Sobriety Tests (SFSTs) for use in DUI investigations. These are the only tests with scientific validation studies supporting their use as evidence of impairment. Maryland law enforcement agencies train officers to administer these tests according to NHTSA's standardized protocols.
1. Horizontal Gaze Nystagmus (HGN)
The HGN test evaluates involuntary eye movement (nystagmus) as the officer moves a stimulus — typically a pen or finger — horizontally across the subject's visual field. The officer looks for six clues: lack of smooth pursuit in each eye, distinct nystagmus at maximum deviation in each eye, and onset of nystagmus prior to 45 degrees in each eye. NHTSA's validation studies indicate that four or more clues correlate with a BAC of 0.08% or higher in approximately 88% of subjects — meaning it is wrong approximately 12% of the time under ideal conditions.
Common administration defects include: failure to check for equal pupil size and resting nystagmus before beginning; moving the stimulus too fast or too slow; failing to hold the stimulus at maximum deviation for the required minimum of four seconds; conducting the test in flashing or strobing light conditions; and failing to properly document the number of clues observed.
2. Walk-and-Turn (WAT)
The WAT is a divided-attention test requiring the subject to walk nine steps heel-to-toe along a real or imaginary line, turn in a specific manner, and return nine steps. Officers look for eight clues: inability to maintain the instructional stance, starting too soon, stopping, failing to touch heel-to-toe, stepping off the line, using arms for balance, an improper turn, and an incorrect number of steps. NHTSA validation indicates two or more clues correlate with BAC of 0.08% or higher approximately 79% of the time.
Common administration defects include: failing to demonstrate the test properly before asking the subject to perform it; administering the test on uneven, sloped, or wet surfaces; failing to ask whether the subject has injuries affecting balance; not providing a real line to walk; and scoring clues that were caused by the environment rather than impairment.
3. One-Leg Stand (OLS)
The OLS requires the subject to stand with one foot raised approximately six inches off the ground and count aloud until told to stop (approximately 30 seconds). Officers look for four clues: swaying, using arms for balance, hopping, and putting the foot down. NHTSA validation indicates two or more clues correlate with BAC of 0.08% or higher approximately 83% of the time.
Common administration defects include: failing to ask about physical conditions affecting balance before beginning; administering the test on uneven or sloped surfaces; conducting the test in strong wind or poor lighting; and improperly counting the time or number of clues.
Officers sometimes administer additional non-standardized field sobriety tests such as the finger-to-nose test, the Romberg balance test, or reciting the alphabet. These tests have no NHTSA validation studies supporting their use as indicators of impairment. They can be challenged as scientifically unreliable and should carry little or no evidentiary weight.
How SFST Results Are Challenged
The defense of field sobriety test evidence proceeds through several avenues:
- Officer certification and training records — The administering officer must be certified in SFST administration. Training records are discoverable and may reveal gaps or deficiencies.
- Deviation from NHTSA protocols — Any deviation from the standardized administration procedure undermines the scientific basis for the test results. Body camera footage often documents these deviations.
- Environmental conditions — Uneven surfaces, poor lighting, weather conditions, and traffic noise all affect performance on divided-attention tests and can be documented through discovery.
- Physical condition of the subject — Age over 65, weight over 50 pounds above ideal, back or leg injuries, and inner ear conditions all affect SFST performance independently of alcohol consumption. NHTSA's own manuals acknowledge these limitations.
- BWC and MVR cross-referencing — Body camera and in-car recording footage frequently shows the actual test performance, which can contradict the officer's written scoring of clues.
SFST Refusal
In Maryland, you may refuse to perform Standardized Field Sobriety Tests. Unlike the evidentiary breath test, refusal of SFSTs does not carry a specific statutory penalty. However, the officer may arrest you based on other observations, and the refusal may be mentioned at trial. Whether to perform or decline field sobriety testing is a situational decision that depends on your physical condition, the environment, and other factors — something an attorney can only advise on prospectively.