Standardized field sobriety tests in North Carolina DWI cases
What the three standardized tests measure, how officers are trained to administer them, and why video and conditions matter.
The three standardized tests
The National Highway Traffic Safety Administration’s standardized battery includes the horizontal gaze nystagmus (HGN), walk-and-turn, and one-leg stand tests. Officers use observed clues as one part of deciding whether probable cause exists to arrest for impaired driving.
These are divided-attention tasks, not pass-or-fail athletic contests. The usefulness of the observations depends on proper instructions, standardized administration, the surface and lighting, footwear, weather, medical or balance conditions, language comprehension, and what the officer recorded.
What a careful review should examine
Body-camera and dashboard video can be more informative than a brief narrative. Counsel may compare the video with the written report, training standards, claimed clues, start position, timing, and whether nonstandard tests were presented as though they were standardized.
Are field tests mandatory?
Physical coordination tests are different from the chemical-test procedures governed by North Carolina’s implied-consent statute. A refusal can nevertheless be offered as evidence under G.S. 20-139.1(f). Whether a requested test was standardized, lawfully requested, fairly administered, or accurately described is a fact-specific legal question.
How the evidence is used
Field observations may be considered with driving, speech, odor, admissions, screening results and other circumstances. No single clue automatically proves impairment, and poor driving is not the only route by which the State may try to establish appreciable impairment.
Frequently asked questions
Does an HGN result prove a specific alcohol concentration?
No. It is an observational field test, not a chemical measurement of blood-alcohol concentration.
Can medical conditions matter?
Yes. Vision, balance, orthopedic, neurological and other conditions may affect particular observations and should be documented.
Should I preserve video quickly?
Yes. Retention policies and discovery timing vary. A prompt request can be important when video may clarify disputed observations.