Carolina Criminal Defense & DUI Lawyer UpdatesThis post continues the Breath, Blood, and Bull series, an in-depth look at how science, procedure, and perception collide in the 
prosecution and defense of DWI cases in North Carolina. The first installment examined the limits of chemical testing. The second article turned to the machines that interpret alcohol breath samples into evidence, using the “breathalyzer.” This post focuses on the field sobriety tests or “SFSTs” that often precede BAC testing.
Standardized Field Sobriety Tests (SFSTs) are a battery of three roadside exercises: Horizontal Gaze Nystagmus (HGN), Walk-and-Turn (WAT), and One-Leg Stand (OLS), designed by NHTSA to gauge impairment.
When prosecutors rely on Standardized Field Sobriety Tests to support a DWI charge, the assumption is that these dexterity exercises offer reliable, objective proof of impairment. Yet the science tells a more complicated story.
screening at the roadside and an evidentiary test under the state’s implied consent laws. These procedures are guided by statutes like G.S. 20-16.2, which defines the expectations placed on a driver once probable cause is established. Although both tests relate to detecting alcohol, they serve different functions and carry different legal consequences.