By Attorney Patrick Apple
If you have been charged with DWI in North Carolina, you were likely asked to perform field sobriety tests on the side of the road before you were arrested. Most people do not know what those tests are actually measuring, what the rules are for administering them, or how much weight they can legally carry. Understanding that can make a significant difference in how your case is defended.
The Standardized Field Sobriety Tests
The National Highway Traffic Safety Administration developed and validated three standardized field sobriety tests for use in DWI investigations. These are the only tests that have been scientifically studied for their ability to detect impairment, and the Administration has established specific protocols that must be followed when administering each one. When officers deviate from those protocols, the reliability of the results is compromised.
The three standardized tests are the Horizontal Gaze Nystagmus test, the Walk and Turn test, and the One Leg Stand test.
Horizontal Gaze Nystagmus
Nystagmus is the involuntary jerking of the eye. Alcohol and certain other substances cause a specific type of nystagmus that becomes more pronounced as impairment increases. The Horizontal Gaze Nystagmus test is designed to detect this by having the officer move a stimulus, typically a pen or finger, horizontally in front of the subject’s eyes while observing for specific clues.
Officers are trained to look for six clues total, three in each eye: lack of smooth pursuit as the eye follows the stimulus, distinct and sustained nystagmus at maximum deviation, and onset of nystagmus prior to a forty-five degree angle. The Administration’s research indicates that four or more clues suggests a blood alcohol concentration at or above 0.08.
The administration requirements are precise. The stimulus must be held at a specific distance from the subject’s face. It must be moved at a specific speed. The officer must hold the stimulus at maximum deviation for a minimum of four seconds. The subject must be checked for equal pupil size and resting nystagmus before the test begins. Failure to follow these protocols does not just reflect poor technique. It means the test was not administered in the manner that the Administration validated, and the results cannot be considered reliable.
It is also worth noting that nystagmus can be caused by factors entirely unrelated to alcohol, including certain medications, inner ear disorders, and neurological conditions. A thorough defense examines whether any of those factors may have been present.
Walk and Turn
The Walk and Turn test is a divided attention test designed to assess whether a subject can listen to and follow instructions while performing a physical task. The subject is instructed to take nine heel-to-toe steps along a straight line, turn in a specific manner, and return nine heel-to-toe steps.
The Administration identifies eight clues officers should observe: cannot keep balance during instructions, starts before instructions are finished, stops while walking, does not touch heel to toe, steps off the line, uses arms for balance, makes an improper turn, and takes the wrong number of steps. Two or more clues is considered indicative of impairment under the Administration’s research.
Proper administration requires that the instructions be given in a standardized way, that the subject be given a reasonable surface on which to perform the test, and that the officer accurately observe and record the clues. Sloped surfaces, uneven pavement, poor lighting, inappropriate footwear, and physical conditions such as leg or back injuries can all affect performance in ways that have nothing to do with alcohol. These factors matter and should be part of any defense analysis.
One Leg Stand
The One Leg Stand test requires the subject to stand on one foot with the other foot raised approximately six inches off the ground while counting aloud for thirty seconds. The Administration identifies four clues: swaying while balancing, using arms for balance, hopping, and putting the foot down. Two or more clues is considered indicative of impairment.
Like the Walk and Turn, this test is significantly affected by physical conditions, surface conditions, and footwear. Age and weight can also be relevant factors. The Administration’s own research acknowledges that the test has reduced reliability for individuals over sixty-five or those with certain physical conditions.
The Portable Breath Test: What It Can and Cannot Do
Officers in North Carolina frequently administer a portable breath test, sometimes called a portable breath test or alcohol screening test, during a roadside DWI investigation. This is a handheld device that provides a preliminary indication of the presence of alcohol.
What many people do not know is that under North Carolina law, specifically G.S. 20-16.3(d), the numerical result of a portable breath test cannot be used by an officer to establish reasonable grounds to believe a driver has committed an implied consent offense such as DWI. The officer can use the test to confirm the presence of alcohol, but the number itself cannot factor into the probable cause analysis.
This is not a technicality. It is a statutory protection with real consequences, as illustrated by the North Carolina Court of Appeals decision in State v. Overocker. In that case, the court affirmed the trial court’s suppression of a DWI arrest where the officer relied in part on the portable breath test result to support probable cause. The court found that the remaining facts, including a light odor of alcohol, an accident that was not the defendant’s fault due to a motorcycle illegally parked behind him, and field sobriety test performance where the only errors were pausing midway through each test to ask for clarification before completing them correctly, were not sufficient to establish probable cause for arrest. The court was clear: a light odor of alcohol, drinks at a bar, and an accident that was not the defendant’s fault were not sufficient circumstances, without more, to provide probable cause to believe the defendant was driving while impaired.
Overocker is a significant case for DWI defense in North Carolina because it illustrates that the probable cause analysis must be grounded in the totality of observable facts, and that improperly relying on a portable breath test result to fill gaps in that analysis is not permitted.
What This Means for Your Case
Field sobriety tests are not pass or fail in the way most people assume. They are observations subject to interpretation, and that interpretation depends entirely on whether the officer followed the protocols the Administration established, whether the conditions were appropriate, and whether there are innocent explanations for the clues the officer observed.
A DWI defense in Guilford County that takes these tests seriously will obtain the officer’s complete training records, all available video footage, the written scoring sheets, and any documentation of the conditions under which the tests were administered. It will examine whether the portable breath test result was improperly factored into the probable cause determination. And it will evaluate the totality of the circumstances the way a court is required to, not just the way the officer presented them in the report.