Standardized Field Sobriety Tests in Indiana Explained: What You Need to Know

Every year, thousands of drivers across the country are stopped on suspicion of Driving While Impaired (DWI) or Driving Under the Influence (DUI). These stops often lead to a crucial decision point—whether or not the officer has probable cause to make an arrest. That decision frequently hinges on a series of tests called the Standardized Field Sobriety Tests (SFSTs).

These roadside tests aren’t just a casual request. They are standardized, validated, and legally significant tools developed and approved by the National Highway Traffic Safety Administration (NHTSA) and the International Association of Chiefs of Police (IACP). Understanding what these tests are, how they work, and what their limitations are can make all the difference if you’re ever pulled over for suspected impaired driving.

What Are Standardized Field Sobriety Tests (SFSTs)?

The SFSTs consist of three validated psychophysical tests designed to evaluate a person’s divided attention capabilities—a key area of impairment in alcohol or drug-influenced individuals. These tests are:

1. Horizontal Gaze Nystagmus (HGN)

2. Walk-and-Turn (WAT)

3. One-Leg Stand (OLS)
   

Each test targets both mental and physical functions, which are often degraded when someone is under the influence of alcohol or other substances. According to the NHTSA SFST manuals, these are the only three tests that have been extensively studied and validated through both laboratory and field research to correlate with blood alcohol concentration (BAC) levels, particularly 0.08% or greater.

Why only these three? Because they are the only ones that meet the criteria for scientific validation, which means they have been shown to consistently yield reliable and accurate indicators of impairment when administered properly.

1. Horizontal Gaze Nystagmus (HGN)

The Horizontal Gaze Nystagmus test is based on a physiological phenomenon—involuntary jerking of the eyes—that becomes more pronounced when a person is intoxicated. During this test, the officer asks the subject to follow a stimulus (usually a pen or flashlight) horizontally with their eyes without turning their head.

The officer looks for three specific clues in each eye:

• Lack of smooth pursuit

• Distinct and sustained nystagmus at maximum deviation

• Onset of nystagmus prior to 45 degrees

If four or more clues are observed, NHTSA research suggests a high probability that the subject’s BAC is 0.08% or greater.

According to the SFST manuals, this test is particularly reliable and often cited by officers and prosecutors due to its objectivity and repeatability when properly conducted.

However, external factors such as wind, flashing lights, or the subject’s medical conditions (such as neurological disorders or eye tremors) can influence results. That’s why correct administration—at eye level, at the correct speed and distance, and with proper instructions—is critical.

2. Walk-and-Turn (WAT)

This is a divided attention test that challenges the subject to simultaneously follow instructions, maintain balance, and perform physical movements. In this test, the person is instructed to:

• Take nine heel-to-toe steps along a straight line

   

• Turn using a series of small steps

• Return with another nine heel-to-toe steps

   

Officers are trained to look for eight specific clues:

1. Cannot balance during instructions

    

2. Starts too soon

    

3. Stops while walking

    

4. Doesn’t touch heel-to-toe

    

5. Steps off the line

    

6. Uses arms for balance

    

7. Improper turn

    

8. Incorrect number of steps

    

The presence of two or more clues correlates with a BAC of 0.08% or greater.

The WAT test is sensitive to both cognitive function and motor control, making it a valuable tool—if conducted properly.

But again, several environmental and individual factors—such as uneven pavement, inclement weather, footwear, age, or weight—can affect a subject’s performance. If the officer fails to account for those, the results could be skewed.

3. One-Leg Stand (OLS)

In this test, the subject must stand on one leg, raise the other foot approximately six inches off the ground, and count aloud (e.g., “one thousand one, one thousand two…”) until instructed to stop, usually at 30 seconds.

Officers observe for four primary clues:

1. Swaying while balancing

    

2. Using arms to balance

    

3. Hopping

    

4. Putting the foot down

    

If two or more clues are observed, this again suggests possible impairment at the 0.08% BAC level or above.

The OLS test is more difficult for individuals with balance issues, physical disabilities, or those over a certain age. The SFST manuals caution that officers should always consider physical limitations and medical conditions when interpreting results.

The SFSTs and the Three-Phase DWI Detection Process

According to NHTSA, the SFSTs are part of Phase Three of the DWI detection process—Pre-Arrest Screening. The full detection process includes:

Phase One – Vehicle in Motion

Officers observe the driver’s behavior while the vehicle is in motion, such as weaving, braking erratically, or driving too slowly.

Phase Two – Personal Contact

This phase includes interaction with the driver—observing their speech, responses, odors of alcohol, and physical condition.

Phase Three – Pre-Arrest Screening

This includes the SFST battery and possibly a Preliminary Breath Test (PBT). The SFSTs help the officer determine if there’s probable cause to arrest the driver for impaired driving.

Why the SFSTs Matter in Court

Field sobriety tests aren’t just for roadside assessments—they often become a central part of DUI/DWI prosecution. Officers are trained to document their observations meticulously and testify to what they saw during the test. That testimony can make or break a case.

The credibility of the officer and whether the SFSTs were administered in accordance with NHTSA training are major issues in court. Even a minor deviation from the proper procedures can affect the admissibility and weight of the evidence.

Common Issues and Legal Defenses

Many people assume that “failing” a field sobriety test automatically means guilt—but that’s far from true. Here are some common factors that can cast doubt on SFST results:

• Non-standardized administration: Officers must follow specific procedures. Improper administration reduces the reliability of the results.

   

• Medical conditions: Neurological issues, injuries, or even fatigue can affect performance.

   

• Environmental factors: Uneven ground, poor lighting, traffic noise, or weather conditions can skew test outcomes.

   

• Bias or subjective interpretation: Some parts of the test are open to subjective judgment, especially when officers expect to find impairment.

   

This is why an experienced attorney—familiar with NHTSA’s SFST standards—can challenge the foundation of the evidence.

How Effective Are SFSTs?

According to research cited by NHTSA:

• The HGN test alone correctly classifies about 88% of individuals with BACs above 0.08.

   

• The Walk-and-Turn is approximately 79% accurate

• The One-Leg Stand comes in at 83% accuracy

Used together as a battery, the SFSTs increase overall reliability, but they are not foolproof. Their accuracy depends heavily on officer training, observation, and adherence to protocol.

General Deterrence and Public Safety

The primary goal of SFST training is to increase deterrence of DWI violations. According to the NHTSA Instructor Manual, this helps reduce the number of crashes, deaths, and injuries caused by impaired drivers. The theory of general deterrence relies on the public’s fear of getting caught. If enforcement is visible and consistent, more people will avoid driving impaired.

But general deterrence only works if:

• Officers are properly trained in detection and testing

   

• Violators are held accountable

• The public perceives a real risk of being caught

   

That’s why SFSTs are part of a nationwide effort to improve traffic safety and save lives.

Conclusion: Know Your Rights, Know the Science

The Standardized Field Sobriety Tests are a serious part of a DUI investigation. While they are rooted in science and standardized training, they are not infallible. A poor performance could be the result of numerous non-alcohol-related factors—and even a properly administered test may not definitively prove impairment.

If you’ve been arrested based on field sobriety test results, it’s essential to work with an attorney who understands the NHTSA guidelines, the limits of SFSTs, and how to analyze police video, reports, and testimony for inconsistencies.

At Marc Lopez Law Firm, we use these same manuals that law enforcement is trained with. We know the rules. More importantly, we know when they’ve been broken—and how to use that to protect your rights.

Facing DUI Charges? Let’s Talk.

Our team is ready to review your case and help you fight back with precision, experience, and the law on your side. Give us a call at 463-842-0409, and remember—always plead the Fifth!