Field sobriety tests (FSTs) are a standard set of physical and cognitive exercises that Tennessee police officers use during traffic stops to help gauge impairment. Standard FSTs include the Horizontal Gaze Nystagmus test, the Walk-and-Turn test, and the One-Leg Stand test. These are designed to measure balance, coordination, divided attention, and eye movement control. In theory, a sober person should complete these tasks with relative ease, while someone under the influence might struggle, indicating impairment.
However, the reality is these tests are far from fool-proof. Field sobriety tests are not an exact science and can be influenced by factors unrelated to alcohol consumption. In fact, the many studies that have been conducted on sobriety tests establish that under perfect conditions, on the proper candidate under proper roadside conditions, the HGN is 88% accurate, W&T 79% and OLS is 83% accurate at detecting impairment above a .08% BAC. Uneven pavement, poor lighting, inclement weather, and even the stress of a traffic stop can cause a sober person to perform poorly. Medical conditions, physical injuries, certain medications, fatigue, or nervousness can also lead to results that do not accurately reflect impairment. FSTs also rely heavily on an officer’s interpretation, which can introduce bias and human error.
In this blog post, we’ll examine how field sobriety tests can produce unreliable evidence, how Tennessee law views their admissibility, and how a skilled DUI defense lawyer can challenge their results in court. Understanding how field sobriety tests work can empower you to build a strong defense strategy with your attorney, protect your driving privileges, and safeguard your future.
Standard Field Sobriety Tests in Tennessee
Let’s take a closer look at the standard field sobriety tests police officers in Tennessee use to determine impairment, including the factors each test is intended to measure, as well as some of their flaws and limitations:
- Horizontal Gaze Nystagmus (HGN) Test
- What It Is: During the HGN test, an officer asks you to follow a small object—like a pen or flashlight—with your eyes while keeping your head still.
- What It Measures: The officer observes your eyes for involuntary jerking movements, known as nystagmus, which can become more pronounced under the influence of alcohol or certain drugs.
- Limitations: Factors such as medical conditions, fatigue, or even flashing lights can cause nystagmus, making the test less reliable. Although 88% accurate, currently Tennessee courts do not allow the vast majority of officers to testify to the observation of HGN, despite it being the most accurate test, because officers cannot provide the jury with the requisite scientific knowledge for why nystagmus occurs when an individual is above a .08% BAC.
- Walk-and-Turn Test
- What It Is: You’re instructed to take nine heel-to-toe steps along a straight line, turn on one foot, and return in the same manner.
- What It Measures: This test assesses your balance, coordination, ability to follow directions, and memory—all functions that can be impaired by alcohol.
- Limitations: Uneven surfaces, inappropriate footwear, or physical disabilities can affect performance, regardless of sobriety.
- One-Leg Stand Test
- What It Is: You must stand on one leg with the other foot approximately six inches off the ground while counting aloud until told to stop, usually for about 30 seconds.
- What It Measures: This evaluates your balance and focus, as impairment may make it difficult to maintain posture and concentration.
- Limitations: Age, weight, inner ear issues, or nervousness can lead to poor performance, unrelated to alcohol consumption.
These tests are designed to be simple for a sober person to perform but challenging for someone who is impaired. They focus on key faculties that can be affected by alcohol and drugs, including balance and coordination, attention and multitasking, and control of eye movement. However, there are many factors that can make field sobriety tests unreliable in court, especially with a skilled DUI attorney investigating your case.
Factors That Can Make Field Sobriety Tests Unreliable
1. Environmental Conditions
Field sobriety tests are often conducted on the side of the road, where the environment can make passing them far more difficult, even for a sober person.
- Uneven or Slippery Surfaces: Gravel, cracks, potholes, and uneven pavement can cause missteps during the Walk-and-Turn or One-Leg Stand test.
- Poor Lighting: Darkness can make it difficult to see the straight line in a Walk-and-Turn test or focus properly on instructions.
- Inclement Weather: Rain, wind, snow, or extreme heat can affect balance, footing, and concentration. These tests are supposed to be conducted on a dry surface.
- Traffic Noise and Distractions: Passing cars, flashing police lights, and nearby noise can create a stressful and distracting environment, making it harder to perform and hear instructions.
These conditions can make even the most coordinated and awake individual appear impaired. If an officer fails to account for environmental challenges, the test results may be unreliable.
2. Physical and Medical Conditions
Certain physical or medical issues can interfere with your ability to perform FSTs, regardless of whether you’ve consumed alcohol or drugs.
- Balance Disorders: Inner ear problems, vertigo, or neurological conditions can affect stability and cause stumbling providing an alternative reason for poor balance rather than alcohol.
- Injuries or Chronic Pain: Leg, back, or foot injuries can make walking or standing on one leg extremely challenging.
- Age and Weight: Older individuals or those with higher body weight may have difficulty performing physical tests designed for younger, physically fit people. Specifically, officers are trained individuals who are 65 years or older (older editions of the officers training manual said 60 years old) or individuals 50 or more pounds overweight are not the appropriate candidate to conduct such tests.
- Medical Conditions Affecting Eye Movement: Conditions like nystagmus (involuntary eye movement), brain injuries, or certain medications can cause a person to “fail” the Horizontal Gaze Nystagmus test without being impaired.
- Head trauma such as concussions commonly cause poor performance on the field sobriety testing. Your DUI attorney should seek any medical records and/or EMT records establishing any injuries resulting from a wreck that may have occurred prior to your arrest.
If you have a pre-existing condition such as these, it is critical that this information is mentioned while consulting with a DUI attorney, as this could become a defense in your case.
3. Improper Instructions or Officer Error
Field sobriety tests must be conducted according to strict guidelines established by the National Highway Traffic Safety Administration. Unfortunately, officers don’t always follow these protocols correctly, leading to unreliable results.
- Vague or Confusing Instructions: If an officer fails to clearly explain the steps of a test, a driver might “fail” due to misunderstanding, not impairment. Officers are trained like any other “standardized test”, the instructions and demonstrations must be proper or it is no longer a standardized test fairly attributing poor performance to alcohol impairment.
- Inadequate Demonstrations: Officers are trained to demonstrate each test before asking a driver to perform it. A poor or rushed demonstration might confuse the driver, leading to inadequate results.
- Bias and Misinterpretation: An officer may unconsciously look for signs of failure, interpreting minor mistakes—such as swaying slightly or miscounting—as evidence of intoxication.
- Failure to Account for Driver’s Condition: Officers should ask if physical or medical issues might affect test performance, but this step is often skipped.
If a DUI attorney can determine that field sobriety tests were improperly administered, this may render the results unreliable and inadmissible in court.
4. Nervousness and Stress
Being pulled over, questioned by police, and asked to perform physical tests can be a very intimidating experience—even if you’re completely sober.
- Stress Response: Nervousness can cause trembling, unsteadiness, or difficulty concentrating—all of which can lead to mistakes during field sobriety tests.
- Pressure to Perform: A person may feel heightened anxiety knowing their performance is being closely scrutinized and could lead to arrest.
- Fear of Failing: Simply the fear of “failing” a test can cause drivers to second-guess instructions, overthink their movements, or appear unsteady.
These psychological factors are completely normal reactions to a high-stress situation, but they are often not taken into account by officers conducting DUI investigations.
5. Non-Alcohol-Related Impairment
There are many reasons why someone might exhibit physical or cognitive behaviors that mimic impairment without consuming alcohol.
- Fatigue: Exhaustion or lack of sleep can cause similar symptoms to intoxication, including bloodshot eyes, poor balance, and delayed responses.
- Medications: Prescription or over-the-counter medications—like antihistamines or pain relievers—can cause drowsiness or other side effects that resemble intoxication.
- Low Blood Sugar (Hypoglycemia) or high blood sugar (Hyperglycemia): People with diabetes or low blood sugar may exhibit confusion, slurred speech, or dizziness. Commonly in diabetes clients our DUI attorneys can demonstrate that the failure and reasons for the client appearing impaired was likely a result of their sugar levels. This is imperative and medical records can potentially help your attorney provide an alternative theory of the case and avoid a DUI conviction.
- Dehydration: A lack of hydration can cause disorientation, shakiness, or lack of focus.
Officers may overlook these alternative explanations, assuming impairment without fully considering other possibilities.
Understanding how field sobriety tests can be unreliable is a first step towards building a strong defense against DUI charges. Depending on the facts of your specific case, there could be factors in addition to what we’ve mentioned above. A DUI defense attorney in Tennessee can carefully analyze the evidence available (such as body cam and dash cam footage), challenge the results of field sobriety tests, and pursue a positive outcome in your case.
How a DUI Defense Attorney Can Challenge Field Sobriety Tests in Tennessee
Questioning the Admissibility of Field Sobriety Test Results
In Tennessee, FST results are not automatically accepted as evidence of impairment. Courts recognize that these tests are subjective and heavily dependent on how they are administered. Your attorney can challenge the admissibility of FST results by:
- Scrutinizing Probable Cause for the Stop:
If the officer lacked reasonable suspicion to stop your vehicle in the first place, all evidence gathered during the stop—including FST results—may be inadmissible in court. - Lack of Reasonable Suspicion for Field Sobriety Tests:
Even if an officer had reasonable suspicion to conduct a traffic stop, it does not automatically provide the officer the right to request field sobriety testing. An officer must have reasonable suspicion, or specific and articulable facts demonstrating more than a mere hunch, that you may be impaired. Although the stop may be justified, there are 24 clues of impairment officers look for during the driving phase to indicate potential impairment. Additionally, officers often state slurred speech, odor of alcohol, unsteadiness on feet, and red, watery bloodshot eyes as reasons to believe the motorist is impaired prior to fields. A lack of such indicators during the personal contact phase, where the officer approaches the window to write you a citation for the traffic infraction, can limit the officers right to move forward to sobriety testing. Your attorney should always call into question whether the officer truly observed those indicators and whether they reach reasonable suspicion of impairment rather than simply consumption. - Highlighting Protocol Violations:
Officers must adhere to the strict guidelines established by the National Highway Traffic Safety Administration when conducting FSTs. Failure to follow these protocols—such as improper instructions, rushed administration, or incomplete demonstrations—can render the results unreliable. - Examining Officer Qualifications:
Your attorney will investigate the officer’s training and experience. If the officer lacks proper certification or has a history of mishandling DUI stops, their credibility can be called into question.
Challenging the Officer’s Observations
Field sobriety tests rely heavily on an officer’s interpretation of your performance, which can be biased or flawed. An experienced defense attorney will:
- Cross-Examine the Arresting Officer:
Through detailed questioning, your attorney can highlight inconsistencies in the officer’s observations, such as exaggerating signs of impairment like swaying, missteps, or confusion. - Use Bodycam or Dashcam Footage:
Video evidence can often tell a very different story than the officer’s report. For example, slight swaying or minor balance issues may look far less severe on video, showing that the officer’s observations were overstated or biased. - Expose Officer Bias:
Some officers may rush to judgment based on preconceived notions, especially if they suspect impairment before administering the tests. Your attorney will bring attention to any indicators of bias or unfair treatment.
Presenting Alternative Explanations for Poor Performance
There are numerous non-alcohol-related reasons a person might perform poorly on field sobriety tests. A skilled attorney will introduce these alternative explanations to undermine the prosecution’s case. Examples include:
- Physical and Medical Conditions:
If you suffer from injuries, chronic pain, vertigo, or neurological disorders, these issues can impair your balance and coordination. Your attorney may introduce medical records or expert testimony to validate this explanation. - Environmental Factors:
Your attorney can argue that uneven pavement, poor lighting, rain, or distracting traffic conditions made it difficult to perform the tests accurately. - Footwear and Clothing:
Wearing inappropriate shoes (like heels or flip-flops) or restrictive clothing can negatively impact performance, regardless of sobriety. - Stress and Nervousness:
Being pulled over and subjected to testing can cause anxiety, trembling, or poor concentration, leading to performance issues unrelated to intoxication.
By presenting these alternative explanations, your attorney can cast doubt on whether the FST results truly indicate impairment.
Using Expert Witness Testimony
In some cases, your attorney may enlist the help of expert witnesses to challenge the scientific validity of field sobriety tests. These experts can:
- Debunk the Reliability of FSTs:
Experts can explain to the court how FSTs are not scientific measurements of impairment and have high failure rates, even among sober individuals. - Address Medical and Physical Factors:
Medical experts can testify to specific conditions that explain poor performance, such as injuries, vision issues, or neurological disorders. - Explain Human Variability:
An expert may highlight that factors like age, weight, or fatigue significantly impact performance on physical tests, making them unreliable indicators of intoxication.
Challenging the Overall Weight of FST Evidence
Field sobriety tests are not conclusive proof of impairment, even when performed under ideal conditions. Your attorney will emphasize the following points:
- FSTs Are Not Scientific: Unlike breath or blood tests, field sobriety tests are not a precise meter of impairment. They cannot measure blood alcohol concentration and are prone to human error.
- Other Evidence May Contradict FST Results: Your attorney will look for inconsistencies in the prosecution’s case, such as a clean breathalyzer result, coherent speech, or appropriate driving behavior that contradicts the alleged impairment.
- Reasonable Doubt: Ultimately, your attorney’s goal is to create reasonable doubt in the minds of the jury or judge by exposing the flaws and unreliability of FSTs.
If you’re facing DUI charges in Tennessee, don’t assume a “failed” field sobriety test seals your fate. An experienced DUI defense lawyer can expose the flaws in these tests and build a strong defense tailored to your specific situation.
Fight DUI Charges With Barnes & Fersten
At Barnes & Fersten, we understand how overwhelming a DUI charge can be, and our attorneys are here to help. With a proven track record in defending clients against DUI charges across Tennessee, our legal team can examine all of the available evidence, scrutinize the results of field sobriety tests, and zealously pursue the best outcome in your case.
Don’t let a single roadside test define your future. Call us today at 865-805-5703 or fill out our contact form for free consultation and take the first step toward peace of mind.
Attorney At Law, Managing Partner
Brandon D. Fersten is an esteemed Knoxville attorney practicing DUI, criminal defense, and juvenile law. Known for his empathetic approach and commitment to his clients, he brings a record of favorable case outcomes including dismissals and not guilty verdicts at jury trials resulting in Brandon being recognized as one of the “Top 40 Under 40” in Criminal Defense, U.S. News’ Best Lawyers: “Ones to Watch,” and Super Lawyers’ “Rising Stars”. Brandon’s professional accolades, combined with his passion for justice, position him as a reliable criminal defense advocate in the East Tennessee legal landscape, including Knox County, Blount County, Sevier County, Roane County, Anderson County, and Cumberland County.
