A roadside balance exercise can’t measure blood alcohol concentration. North Carolina DWI field sobriety tests give an officer observations to work with, but they don’t automatically establish impairment or determine what happens next in a case. Understanding what these tests actually measure and where they fall short matters when building a defense.
In Monroe, NC, roadside testing is one piece of a larger picture that can include the reason for the stop, driving behavior, statements made, and later breath or blood testing. We’ve practiced law in Monroe since 1985, and our review of any DWI case begins with the stop itself. Field sobriety testing, the arrest, and chemical testing procedures all get scrutinized as part of our DWI defense work. Here’s what you should know about how these tests work and what can go wrong with them.
What Field Sobriety Tests Actually Measure
Standardized Field Sobriety Tests are roadside exercises designed to help officers observe coordination, balance, attention, and eye movement. The three commonly used standardized tests are Horizontal Gaze Nystagmus, Walk & Turn, and One Leg Stand. North Carolina’s Forensic Tests for Alcohol Branch, within the Division of Public Health, provides law enforcement training and refresher courses in these procedures.
These exercises are distinct from both the portable breath test and the chemical test administered after arrest. A portable breath test is a small roadside device that may return an alcohol reading; a chemical analysis after arrest involves breath or blood testing under the state’s implied consent process. Field exercises don’t produce a direct blood alcohol concentration number.
An officer may use observations from these tests when deciding whether probable cause exists to make an arrest. A probable cause finding is a reasonable basis to believe a crime may have occurred. Test performance can be one factor in that decision, but it’s rarely the only one.
How Each Test Works
The National Highway Traffic Safety Administration has developed standardized procedures for all three exercises. That standardization matters because the officer’s instructions, demonstration, timing, and observation method all affect what the exercise can actually show.
Horizontal Gaze Nystagmus
This test involves observing involuntary jerking of the eyes as they track a moving stimulus, typically a pen or finger. The officer watches each eye for specific movements at particular angles. Eye conditions, contact lenses, medical issues, flashing lights nearby, and whether the officer followed the prescribed procedure can all affect how this observation is evaluated.
Walk & Turn
The Walk and Turn asks a person to listen to instructions, hold a starting position, take heel-to-toe steps along a line, turn in a specified way, and return. Officers are trained to note clues such as starting too soon, missing heel-to-toe contact, stepping off the line, using arms for balance, taking the wrong number of steps, or turning incorrectly. Because the exercise combines physical balance with the ability to follow a sequence of directions, difficulty with one part doesn’t automatically point to alcohol impairment.
One Leg Stand
The One Leg Stand requires raising one foot while counting according to the officer’s instructions. Observations may include swaying, hopping, putting the foot down, or using the arms for balance. How the officer delivers the directions, including when to begin, where to look, how high to raise the foot, and how long to hold it, matters as much as the performance itself.
What Can Affect Performance
Roadside conditions aren’t controlled environments. An injury, chronic pain, fatigue, anxiety, age, a balance disorder, a neurological condition, or an inner ear issue can all affect how someone performs these exercises. Footwear and restrictive clothing are often visible on dash camera and body-worn camera footage and can be relevant to what an officer records as a clue.
Factors that may affect roadside exercise performance:
- Testing Surface: Sloped pavement, loose gravel, cracked asphalt, or the absence of a visible line can affect the Walk and Turn.
- Weather and Lighting: Rain, wind, darkness, vehicle headlights, and emergency lighting can interfere with balance and visual focus.
- Physical Condition: Injuries, mobility limitations, illness, fatigue, and medical conditions can all produce movements an officer records as clues.
- Instructions and Demonstration: Unclear directions, an incomplete demonstration, or the officer’s positioning during the test can affect whether the exercise was conducted as intended.
A perceived pass or failure doesn’t settle whether a driver was appreciably impaired, meaning their physical or mental faculties were noticeably reduced by an impairing substance. These observations have to be weighed against everything else in the record.
Are These Tests Required?
Roadside field sobriety exercises are different from chemical testing under implied consent. Implied consent applies to chemical testing after a DWI arrest, and refusing a requested chemical test carries separate legal consequences. A driver isn’t required by implied consent to perform roadside coordination or eye-movement exercises. That said, decisions made during a traffic stop can have real practical consequences, and there’s no single right answer that fits every situation. Individualized legal advice after an arrest or charge is important precisely because the details vary.
How We Review Field Sobriety Tests in a DWI Case
Our review often begins before the officer ever asked the driver to step out of the vehicle. The reason for the stop, the officer’s initial observations, the sequence of the investigation, and the basis for the arrest are all evaluated alongside the field sobriety exercises themselves.
Video is frequently the most useful tool in this process. Dash camera and body-worn camera footage can show pavement conditions, lighting, traffic, footwear, physical movements, officer instructions, and how the exercises were actually performed. Details a written report may not capture fully are often visible on video. We examine whether the officer gave standardized instructions and whether what was recorded in the report matches what the video actually shows. When the case calls for it, we work with professionals such as private investigators and digital forensic examiners to build a defense tailored to the specific evidence.
Field sobriety tests tell only part of the story. Their significance depends on the testing conditions, how each exercise was administered, and how those observations fit with the rest of the evidence. If you’re facing a DWI charge in Monroe, Charles B. Brooks II Attorney at Law can review the stop, available video, and testing procedures with you. Reach us at (704) 271-2141 to discuss your case.