South Dakota DUI Field Sobriety Test
The Three Standardized Tests
When a South Dakota officer suspects DUI during a traffic stop, they typically ask the driver to perform Standardized Field Sobriety Tests (SFSTs) developed by the National Highway Traffic Safety Administration. There are three:
Horizontal Gaze Nystagmus (HGN): The officer holds a stimulus — usually a pen or small flashlight — about 12 inches from your face and moves it slowly from side to side. They're watching your eyes for involuntary jerking (nystagmus) that becomes more pronounced with alcohol impairment. The test looks for six clues across both eyes: lack of smooth pursuit, distinct nystagmus at maximum deviation, and onset of nystagmus before 45 degrees.
Walk-and-Turn: You take nine heel-to-toe steps along a straight line, turn on one foot, and take nine steps back. The officer watches for eight clues: starting too early, losing balance during instructions, stopping while walking, failing to touch heel-to-toe, stepping off the line, using arms for balance, turning incorrectly, and taking the wrong number of steps.
One-Leg Stand: You raise one foot approximately six inches off the ground and count aloud for 30 seconds. The officer looks for four clues: swaying, using arms for balance, hopping, and putting the foot down.
Can You Refuse Field Sobriety Tests?
Yes. Field sobriety tests are voluntary in South Dakota. You are not legally required to perform them, and refusing does not carry the same penalties as refusing the evidentiary chemical test at the station.
The distinction matters because people routinely conflate two different refusals:
Roadside field sobriety tests and the preliminary breath test (PBT): These are investigative tools. Declining them does not trigger implied consent penalties. The officer may still arrest you based on other observations — your driving pattern, odor of alcohol, slurred speech, or statements you made.
Evidentiary chemical test at the station (Intoxilyzer breath test or blood draw): This is the test covered by South Dakota's implied consent law. Refusing this test triggers an automatic one-year administrative license revocation through DPS — a consequence entirely separate from the criminal case.
How Field Sobriety Test Results Are Used in Court
SFST results serve two roles in a South Dakota DUI prosecution:
Establishing probable cause for arrest: The officer uses your test performance to justify the arrest itself. If the defense challenges probable cause through a motion to suppress, the SFST results are a central piece of evidence the prosecution relies on.
Evidence of impairment at trial: If the case goes to trial, the officer testifies about your performance on each test. The prosecution uses the clue count (out of the maximum possible) to argue impairment. Defense attorneys counter by questioning the testing conditions — uneven pavement, poor lighting, wind, the driver's footwear, medical conditions affecting balance, or the officer's deviation from standardized administration protocols.
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Problems with Field Sobriety Tests
SFST evidence is far from bulletproof, and experienced defense attorneys regularly challenge it:
Medical conditions and physical limitations. Inner ear disorders, back injuries, knee problems, obesity, and neurological conditions can all produce false clues on the walk-and-turn and one-leg stand. Even age affects performance — NHTSA's own research validated the tests primarily on subjects between 18 and 65.
Environmental factors. Tests administered on gravel, sloped surfaces, in heavy wind, or under flashing patrol car lights produce unreliable results. The standardized protocols require a dry, level, well-lit surface — conditions rarely met on a South Dakota highway shoulder at 1:00 AM.
Officer training and administration errors. SFSTs must be administered exactly according to NHTSA protocol to maintain their validated accuracy. Officers who rush instructions, demonstrate incorrectly, or score non-standard clues undermine the evidentiary value of the results.
The HGN test is a medical examination. Some defense attorneys argue that HGN testing constitutes a medical procedure that an officer without medical training is unqualified to administer or interpret. While courts generally admit HGN evidence, the argument can be effective in front of a jury.
What This Means for Your Case
If you've already been arrested and either took or declined field sobriety tests, the results are part of the evidence your attorney will work with during plea negotiations or trial preparation. The test results alone don't determine the outcome — they're one piece of a case that includes the reason for the stop, the chemical test results, video evidence, and the officer's report.
The South Dakota First-Offense DUI Guide covers the full evidence-gathering and court process from arrest through sentencing, including how field sobriety evidence fits into the broader defense and plea negotiation framework.
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