What Evidence Matters in Field Sobriety Tests?
Sept. 16, 2025
Field sobriety tests are often one of the first tools law enforcement officers use when they suspect a driver is impaired. These tests are intended to help determine whether someone may be under the influence of alcohol or drugs.
However, not all field sobriety test results are as reliable as they appear. Understanding what evidence matters in field sobriety tests is a critical part of building a strong criminal defense.
The Purpose of Field Sobriety Tests
Field sobriety tests are designed to assess coordination, balance, attention, and the ability to follow instructions. Officers use these tests during traffic stops to help determine whether there is probable cause for an arrest. While several types of tests are used, only a few are recognized as standardized by the National Highway Traffic Safety Administration (NHTSA).
Standardized Tests Most Often Used
There are three main standardized field sobriety tests:
Horizontal gaze nystagmus (HGN): This test tracks involuntary eye movements while the officer moves a pen or light in front of the driver’s eyes.
Walk-and-turn: The driver is asked to walk in a straight line, heel-to-toe, turn on one foot, and return the same way.
One-leg stand: The individual must stand on one leg while counting out loud until told to stop.
These tests are considered to have some level of reliability, but they are still subject to interpretation and outside factors.
Non-Standardized Tests and Officer Discretion
In some cases, officers may use non-standardized tests, which aren't officially recognized by NHTSA. These can include:
Touching the nose with eyes closed
Reciting the alphabet
Counting backward
These tests are generally less reliable and more open to subjective judgment. Because they're not backed by federal guidelines, their results are easier to challenge in court as part of a criminal defense strategy.
Factors That Affect Test Results
Several factors can influence how someone performs on field sobriety tests. These factors often have nothing to do with alcohol or drug use, yet they can still lead to a failed test.
Common Influences on Performance
Medical conditions: Inner ear problems, neurological disorders, or leg injuries can all impact balance and coordination.
Age and weight: Older individuals or those with higher body weight may struggle with the physical movements required by the tests.
Weather and surface conditions: Rain, wind, uneven pavement, or gravel can make performing tests more difficult.
Footwear: High heels, flip-flops, or boots may interfere with balance.
Fatigue or anxiety: Stress, nerves, or tiredness can cause a person to appear impaired when they are not.
Because these variables are common, challenging the circumstances of a field sobriety test is a key aspect of criminal defense.
Officer Conduct and Protocol
The way a field sobriety test is administered can significantly impact the results. Officers are required to follow specific protocols when conducting standardized tests, and failure to do so can call the reliability of the results into question.
Mistakes Officers May Make
Improper instructions: If the driver isn’t clearly told what to do, any mistakes during the test may not reflect impairment.
Skipping medical questions: Officers should ask whether the driver has medical conditions that could affect performance.
Bias or preconceived judgments: If an officer already believes someone is impaired, they may interpret actions unfairly.
Proper administration matters because field sobriety test results often become evidence in court. If a criminal defense lawyer can show that the officer deviated from protocol, the credibility of the test can be diminished.
The Importance of Video Evidence
Most modern law enforcement vehicles are equipped with dashboard cameras, and body-worn cameras are becoming more common. Video recordings can play an important role in evaluating what happened during the traffic stop and sobriety testing.
What Video Can Show
Officer instructions: Whether directions were clear and complete
Driver’s behavior: Whether the person appeared coherent or confused
Environmental conditions: Lighting, traffic, or road surfaces
Timing and context: Whether the test was administered after a long delay
Video footage can support a criminal defense argument that the field sobriety test wasn’t administered fairly or that the driver didn’t appear impaired despite the officer’s claims.
Chemical Tests vs. Field Sobriety Tests
It’s important to distinguish between field sobriety tests and chemical tests such as breathalyzers or blood draws. While field tests are based on observation, chemical tests are considered more objective and are often used later to confirm impairment.
Legal Implications of Each Type
Field sobriety tests: Can provide probable cause for arrest, but are subjective
Chemical tests: Required by implied consent laws and used as evidence of BAC (blood alcohol content)
If a driver refuses to take a chemical test, they may face automatic license suspension. However, field sobriety test refusal doesn't carry the same automatic penalties in many states. This distinction can influence how a criminal defense case is built.
Probable Cause and Arrest Decisions
Officers must have probable cause before making an arrest for impaired driving. Field sobriety test results are often used to establish this. However, if the test is flawed or improperly conducted, the arrest may be challenged.
Other Sources of Probable Cause
Erratic driving behavior
The smell of alcohol or drugs
Open containers in the vehicle
Admissions from the driver
Field sobriety test performance is just one part of a larger picture. A strong criminal defense may include challenging the validity of all evidence presented.
The Science Behind Field Sobriety Tests
While standardized tests have been studied, they are far from foolproof. The original research behind these tests was limited in scope and hasn’t always held up under scrutiny.
Limitations in the Research
Small sample sizes: Initial studies included relatively few participants
Controlled settings: Tests were often done in ideal conditions, unlike real-world stops
Subjectivity: Officer interpretation still plays a large role in scoring results
These scientific limitations allow room for defense attorney to question how reliable the tests truly are in each unique case.
Strategies for Criminal Defense
When someone is charged with driving under the influence (DUI) or operating while intoxicated (OWI), their defense often starts with examining the traffic stop. Field sobriety tests are usually the centerpiece of that stop.
Common Defense Tactics Include:
Challenging the test conditions: Weather, lighting, and road conditions can all be relevant
Reviewing officer behavior: Any deviation from standard protocol weakens the evidence
Using video recordings: To contradict or confirm the officer’s report
Pointing to alternative explanations: Medical issues or nervousness can mimic impairment
These strategies are used to build reasonable doubt and protect the client’s rights under criminal defense law.
Why Legal Representation Matters
Field sobriety tests are just one piece of evidence, but they often carry significant weight. Without legal representation, a person may not know what rights they have or how to challenge the evidence against them.
A Criminal Defense Lawyer Can:
Request discovery: To obtain video, police reports, and other relevant materials
File motions to suppress: To try to exclude improperly obtained evidence
Negotiate plea deals: If a full trial isn’t in the client’s best interest
Prepare for trial: When going to court is necessary
Having someone experienced in criminal defense can make a meaningful difference in how a DUI or OWI case is resolved.
When a Permit Application Is Denied
Anyone facing charges related to field sobriety test results should speak to a criminal defense lawyer as soon as possible. The earlier legal representation is involved, the more time there's to protect rights and challenge flawed evidence.
At Douglas A. Ball, Attorney at Law, we represent individuals in Batavia, Ohio, and throughout Clermont, Hamilton, Brown, and Warren counties, helping them navigate DUI and OWI charges with a focus on challenging the validity of field sobriety test results.