Standardized Field Sobriety Tests (SFSTs) are a critical component of DUI investigations, developed by the National Highway Traffic Safety Administration (NHTSA) and the International Association of Chiefs of Police. These roadside evaluations consist of three validated tests: the Horizontal Gaze Nystagmus (HGN), the Walk-and-Turn (WAT), and the One-Leg Stand (OLS). Each is designed to assess both physical coordination and cognitive function—abilities commonly impaired by alcohol or drugs. Officers use these tests during the pre-arrest screening phase to establish probable cause for DUI arrests. While considered reliable when properly administered, SFSTs are not foolproof. Factors such as medical conditions, environmental influences, and improper administration can all impact the results and their admissibility in court.
In DUI cases, SFST results often become a central issue during prosecution, with officer training and procedural accuracy under scrutiny. Even small deviations from standardized procedures can weaken the reliability of the evidence. Despite NHTSA-reported high accuracy rates—88% for HGN, 79% for WAT, and 83% for OLS—the outcome of these tests is not definitive proof of impairment. An experienced attorney can challenge test results by identifying inconsistencies, examining body cam footage, and pointing out errors in how the tests were conducted. At Marc Lopez Law Firm, attorneys use the same SFST manuals that train law enforcement to help defend their clients, enabling them to spot mistakes and defend clients effectively. If you’re facing DUI charges, understanding these tests—and your rights—is crucial to building a strong defense.