The Three Standardized FSTs
The NHTSA has validated three field sobriety tests: Horizontal Gaze Nystagmus (HGN), Walk-and-Turn (WAT), and One-Leg Stand (OLS). Only these three have research supporting reliability as impairment indicators — and all three have strict administration protocols.
HGN — Horizontal Gaze Nystagmus
The officer moves a stimulus horizontally and observes involuntary eye jerking. Officers must maintain precise stimulus distance and speed, proper lighting, and exact NHTSA sequencing. Deviations are common and documented in our cross-examination. HGN can also be caused by inner ear disorders, certain medications, and neurological conditions unrelated to alcohol.
Walk-and-Turn
The test must be administered on a hard, dry, level surface with a visible line. Testing on gravel, sloped pavement, or grass invalidates it. Subjects over 65, with leg injuries, or with inner ear issues cannot reliably perform this test regardless of sobriety.
One-Leg Stand
Same surface requirements. Subjects overweight by 50+ pounds or over 65 cannot reliably perform OLS. Improper demonstration by the officer, or failure to give instructions before demonstration, are protocol violations we document and argue.
Call (801) 627-1110 to discuss your FST results. We review every case for protocol violations. Free case assessment 24/7.