Field Sobriety Tests: How They Work and Why They Fail

Facing a DUI charge often begins with field sobriety tests (FSTs), a series of exercises designed to help law enforcement assess whether a driver is impaired. These tests are commonplace and play a crucial role in DUI investigations, yet their design and administration are not without controversy. Criticism about their accuracy and fairness has spurred ongoing legal debates and research into their validity.

This blog post explores the purpose of field sobriety tests, why people might fail them, and how to challenge their results if you find yourself accused of driving under the influence. Whether you need a better understanding of the legal process or want to know your rights, this guide offers valuable insights into the complex world of FSTs.

What Are Field Sobriety Tests?

Field sobriety tests are physical and cognitive exercises used by law enforcement to determine whether a driver is impaired due to alcohol or drugs. They are primarily conducted during traffic stops when officers suspect a motorist of being under the influence. Developed by the National Highway Traffic Safety Administration (NHTSA), these tests aim to identify signs of intoxication by evaluating balance, coordination, attention, and divided focus.

Standardized Field Sobriety Tests

Three tests are considered "standardized," meaning they have been tested for supposed reliability when conducted under specific guidelines. These tests include:

1. Horizontal Gaze Nystagmus (HGN)
   The HGN test measures involuntary eye movement, which can occur under the influence of alcohol or drugs. Officers ask the suspect to follow a moving object, such as a pen or flashlight, without moving their head. Indicators include jerking movements of the eyes or difficulty focusing smoothly on the object.
2. Walk and Turn (WAT)
   This test assesses balance, coordination, and the ability to follow instructions simultaneously. An officer will instruct the person to take nine heel-to-toe steps along a straight line, pivot, and return in the same manner. Officers watch for "clues" such as stepping off the line, missing heel-to-toe contact, starting too soon, or losing balance.
3. One Leg Stand (OLS)
   The individual is asked to stand on one foot while counting aloud for 30 seconds. Indicators of impairment include swaying, using arms for balance, hopping, or putting the foot down to regain stability.

While these tests aim to provide a quantifiable way to assess impairment, their connection to actual driving ability or blood alcohol content (BAC) is, at times, tenuous. Studies have shown mixed results in linking test performance to impairment levels, making them a target for legal challenges.

Non-Standardized Field Sobriety Tests

Some law enforcement officers may use additional, non-standardized tests such as reciting the alphabet backward, counting fingers, or balancing coins on the tips of fingers. These tests are less reliable and not backed by scientific research, potentially making their results easier to challenge in court.

Why People Fail Field Sobriety Tests

Failure on a field sobriety test does not automatically indicate intoxication. Numerous factors, both internal and external, can contribute to poor performance. Understanding these reasons can help you see why even sober individuals may struggle during these assessments.

1. Medical Conditions

Certain medical conditions can mimic signs of intoxication. For example:

• Resting Nystagmus: A natural condition where the eyes jerk when focused, unrelated to alcohol or drugs, can lead to a false positive during the HGN test.
• Inner Ear Issues or Vertigo: Balance disorders often cause instability during the OLS or WAT.
• Joint or Muscular Problems: Conditions such as arthritis or injuries to knees, back, or feet may affect a person’s ability to walk in a straight line or balance on one foot.

2. Improper Administration

The effectiveness of these tests depends on strict adherence to procedural guidelines. According to the NHTSA, the HGN test alone has 10 specific steps, while WAT has 17 steps, and OLS has 13 steps. Failing to follow these procedures can result in inaccurate results. For example:

• An officer may forget to instruct the suspect to keep their arms down during the WAT.
• Improperly calibrated equipment or failure to check for medical conditions could compromise HGN results.
• Rushed instructions or failure to demonstrate the tasks can set individuals up for failure.

3. Environmental Factors

Field sobriety tests are often conducted roadside, where conditions are far from ideal. Environmental factors that make it difficult to perform the tests properly include:

• Uneven Surfaces: Gravel, sloped roads, or potholed streets may cause balance issues.
• Poor Lighting: Dim or overly bright lighting can make it hard to follow instructions or maintain focus.
• Weather Conditions: Strong winds, rain, or ice-covered pavement can hinder performance.

4. Psychological Stress

Traffic stops can be nerve-wracking, even for law-abiding citizens. Anxiety, fear, or confusion may cause some individuals to overthink their actions or freeze under pressure. Officers rely on clear directions during FSTs, so misunderstandings are sometimes seen as evidence of impairment.

5. Fatigue or Sobriety-Related Symptoms

Fatigue from a long day or unusual symptoms from illness can lead to failed tests. For instance:

• A sober individual operating on minimal sleep may sway or lose balance during the OLS.
• Congestion or sinus issues can cause eye movement irregularities, triggering false positives on the HGN.

Challenging Field Sobriety Test Results

If you’ve been charged with a DUI based on field sobriety test results, there are ways to dispute the validity of these tests and reduce or even dismiss your charges. Here’s how attorneys approach such challenges.

1. Objecting to Improper Administration

A frequent avenue for challenging FSTs involves demonstrating how the tests were improperly administered. By reviewing dashcam or bodycam footage, your lawyer can identify instances where law enforcement officers failed to follow strict procedural guidelines.
For example, if the officer failed to demonstrate the WAT properly, this could render the results invalid.

2. Questioning Officer Training

FST accuracy relies heavily on the officer’s training and experience. By investigating whether the administering officer had adequate training or certifications, your attorney can raise questions about the legitimacy of their conclusions. Mistakes stemming from inexperience may lead to overruling the test results.

3. Raising Medical or Physical Conditions

Documentation from medical records can demonstrate that you have a condition that influenced your performance. For instance, someone with vertigo could argue that their shaky walk during WAT was unrelated to intoxication.

4. Highlighting Environmental and Situational Factors

The roadside environment plays a critical role in FST outcomes. Your attorney may gather photographic evidence or witness testimony to establish that an uneven surface, lack of light, or extreme weather impacted your abilities during the tests.

5. Cross-Examining Test Bias

A 1994 study revealed that officers sometimes judged individuals as impaired simply because they performed FSTs, compared to “normal-abilities tests” like reciting an address. This underscores the role of bias and preconceived notions. A skilled attorney can use this evidence to argue that results were subjective and not reflective of actual impairment.

6. Utilizing Expert Witnesses

Expert witnesses can play a pivotal role in challenging FSTs. For instance:

• Toxicologists can discuss how test results lack meaningful correlation to BAC levels.
• Former Officers may testify regarding the fallibility of FST administration or interpretation.

7. Suppressing Evidence

If procedural mistakes occurred during your traffic stop, such as lack of probable cause or mishandled arrest protocols, your attorney might be able to suppress the evidence. Without valid results from FSTs, much of the case against you may fall apart.

Final Thoughts

Field sobriety tests are a pivotal part of DUI law enforcement, but they are far from foolproof. Understanding the limitations, biases, and factors that can influence performance provides crucial tools for building your defense. From improperly administered tests to environmental barriers or medical conditions, there are many reasons to challenge the results if you’ve been accused of driving under the influence.

If you are facing charges, consulting an experienced DUI attorney is your best course of action. Many attorneys offer free consultations, giving you a chance to discuss your situation and evaluate the best path forward. A proper legal defense can mean the difference between a damaging conviction and a fair outcome.

For additional guidance or immediate assistance, reach out to a knowledgeable lawyer today. Remember, failing a field sobriety test doesn’t mean your case is a lost cause. If you're facing DUI charges or have questions about field sobriety tests, don’t hesitate to talk to an experienced DUI lawyer immediately about how to fight your case in court and at DMV.