A roadside test can be recorded as a failure even when the video, instructions, surface conditions, or a driver’s physical limitations tell a more complicated story. Field sobriety testing produces observations, not a chemical measurement of alcohol or a final legal determination of impairment. That distinction shapes nearly every DUI defense.
A Tennessee DUI case can turn on several separate questions: whether the stop was lawful, whether the detention lasted too long, whether the tests were properly administered, and whether the officer’s conclusions match the available evidence. A poor performance on one roadside exercise doesn’t close those questions.
For more than 35 years, we’ve defended people facing serious criminal charges. Our team is led by an attorney who holds a board certification in Criminal Law Advocacy from the National Board of Trial Advocacy, and we approach DUI allegations with the same trial-ready review of reports, video, and constitutional issues that high-stakes criminal cases require.
What Field Sobriety Tests Actually Measure
Standardized Field Sobriety Tests are roadside exercises designed to help an officer identify clues associated with impairment. They’re commonly associated with National Highway Traffic Safety Administration, or NHTSA, training protocols, but they don’t directly measure a person’s blood alcohol concentration.
The three tests most often at issue in a Tennessee DUI investigation are the Horizontal Gaze Nystagmus test, the Walk and Turn test, and the One Leg Stand test. Horizontal Gaze Nystagmus, often called HGN, involves an officer watching a person’s eyes for involuntary jerking as the person follows a moving object. The Walk and Turn and One Leg Stand tests assess divided attention: the ability to follow directions while performing physical tasks.
These exercises differ from breath or blood testing. Tennessee’s Implied Consent Law addresses chemical testing after a DUI arrest under circumstances set by law, while roadside field sobriety tests involve an officer’s observations before or around an arrest. The rules governing chemical testing don’t make field sobriety results conclusive.
The First Challenge: Was the Stop & Detention Lawful?
A defense challenge can begin before the officer ever gives a roadside instruction. Police generally need reasonable suspicion (specific, articulable facts suggesting criminal activity may be occurring) to make a traffic stop. An alleged traffic violation, unusual driving pattern, equipment issue, or other observed circumstance may be offered as the basis for that stop.
A defense review examines what the officer actually saw, when the observation occurred, and whether video supports the account. In Memphis, dashboard video, body camera footage, dispatch records, and the citation can help establish the full sequence from initial observation through the stop.
The duration of the detention matters too. An officer can’t extend a routine traffic stop without a lawful reason to continue investigating. Probable cause (a sufficient factual basis to believe a crime has been committed) is evaluated under the totality of the circumstances. Tennessee courts consider driving behavior, an officer’s observations, statements, odor, speech, appearance, and field sobriety performance together. No single roadside clue automatically decides the issue.
Problems with How the Tests Were Administered
Standardized testing only carries its intended value when an officer follows applicable procedures closely. Instructions, demonstrations, timing, scoring, and documentation can all affect whether the reported clues accurately reflect what happened at the roadside.
Instructions & Demonstrations
The Walk and Turn test depends on a person understanding where to stand, when to begin, how many steps to take, when to turn, and how to hold their arms. If an instruction was rushed, unclear, contradicted by a demonstration, or omitted altogether, a recorded mistake may say more about communication than impairment.
Roadway & Lighting Conditions
A level, dry, safe surface isn’t always available beside a roadway. Uneven pavement, loose gravel, rain, wind, passing traffic, poor lighting, and flashing emergency lights can all affect balance and concentration. Video and photographs may reveal conditions the arrest report barely mentions or ignores entirely.
Reports & Recorded Video
Written reports often compress a lengthy encounter into a few sentences. Body camera footage can show the exact wording of instructions, the condition of the roadway, how long a person had to respond, and whether the officer’s report accurately describes the performance. Memphis Police Department policy materials describe documentation requirements for DUI technician observations during standardized testing, making recorded footage an important part of any review.
Physical & Personal Factors That Can Affect Performance
A person can struggle with roadside exercises for reasons unrelated to alcohol or drugs. The relevant question isn’t simply whether someone stepped off a line or put a foot down. The question is whether a physical, medical, or situational factor explains the performance.
Medical Conditions
Injuries, chronic pain, balance disorders, neurological conditions, mobility limitations, and certain medications can affect coordination or eye movements. Medical records, prescription information, and prior treatment history may provide context if they relate to the condition present during the stop.
Footwear & Fatigue
Heeled or unstable footwear, exhaustion after a long shift, or a recent physical injury can affect balance-based testing. Photographs, video, and footwear documented at booking may be useful when these details are disputed.
Communication Barriers
Anxiety, hearing limitations, language barriers, and difficulty processing multi-step instructions can affect how someone responds at a roadside stop. These circumstances don’t independently prove impairment, but they matter when an officer interpreted missed instructions or delayed responses as test clues.
A general claim that a person was nervous or had a bad knee is usually less useful than evidence connected to the event itself. A careful defense review compares the explanation with video, witness accounts, photographs, medical documentation, and the officer’s own notes.
How Tennessee Courts Treat Field Sobriety Results
Field sobriety evidence can be challenged in more than one way. One approach is a motion to suppress: a formal request asking the court to exclude evidence obtained through an unlawful stop, detention, search, or seizure. If the initial stop lacked reasonable suspicion or the detention was unlawfully extended, the question becomes whether the resulting evidence should be excluded entirely.
A separate challenge addresses the reliability and weight of the test results. Even if the stop and detention were lawful, the defense can argue that the officer administered the exercises incorrectly, that conditions undermined the testing, or that the report overstated what the video shows. That argument may affect how much significance a judge or jury gives the results rather than whether the evidence is excluded at all.
Tennessee appellate decisions treat field sobriety performance as one factor in the full probable cause analysis, not an automatic pass-or-fail rule. A reported failure doesn’t establish impairment. It’s a piece of evidence subject to the same scrutiny as everything else in the record.
What a Memphis DUI Defense Review Should Examine
A useful review starts with the complete record, not the officer’s conclusion. DUI cases in Memphis and Shelby County move through the Tennessee criminal court system, where suppression issues and probable cause challenges are litigated through motions and hearings.
Core evidence to review:
- Traffic Stop Materials: The citation, arrest report, dispatch records, and any video showing the driving conduct or reason for the stop.
- Roadside Test Evidence: Body camera footage, dashboard video, recorded instructions, timing, lighting, weather, pavement conditions, and officer notes.
- Officer Information: Training records, DUI technician documentation, and the scoring or observations attributed to each test.
- Personal Context Evidence: Medical records, photographs, footwear, witness accounts, and documentation of injuries or communication limitations.
- Chemical Test Records: Breath or blood testing materials, where applicable, reviewed separately from the field sobriety evidence.
Comparing these sources often reveals important gaps. A report may describe a person as unable to follow instructions while video shows incomplete directions. An officer may characterize a surface as level while footage shows a sloped shoulder near moving traffic. Those details don’t dictate a single outcome, but they can materially shape the legal and factual analysis.
Field Sobriety Results Are One Piece of Evidence, Not the Whole Case
A field sobriety result is a starting point for examination, not a substitute for analyzing the entire stop and arrest. The lawfulness of police conduct, the quality of the instructions, the conditions at the scene, a driver’s physical limitations, and the available video can all change how the evidence looks when scrutinized in court.
If you’re facing a DUI charge in Memphis, Ferguson McNeil Law Firm, P.A. can review the circumstances of your stop and walk through your legal options in a free consultation. We also provide Spanish language services. Reach our team at (901) 878-5434.