What Are Field Sobriety Tests?

Field sobriety tests (often called "SFSTs" or "Standardized Field Sobriety Tests") are a series of physical and mental exercises that law enforcement officers commonly use during DUI investigations to help determine whether they believe a driver is impaired. These tests are typically administered after an officer has made contact with a driver and observed signs that the officer believes may be consistent with alcohol or drug impairment.

Many people mistakenly believe that field sobriety tests are scientific tests that can definitively determine whether a person is under the influence of alcohol or drugs. They are not. Instead, they are investigative tools that officers use, along with their observations, driving behavior, statements made by the driver, physical appearance, and the results of any chemical testing, to help decide whether probable cause exists to make a DUI arrest.

The National Highway Traffic Safety Administration (NHTSA) has developed standardized procedures for administering three specific field sobriety tests. These procedures are intended to promote consistency in how the tests are conducted and interpreted. Because the standardized procedures are important to the reliability of the tests, officers receive specialized training on how the tests should be administered.

Even when properly administered, however, field sobriety tests do not directly measure a person's blood alcohol concentration, nor do they determine whether someone is legally guilty of DUI. Numerous factors unrelated to alcohol or drug use—including age, medical conditions, injuries, fatigue, anxiety, uneven surfaces, weather conditions, footwear, lighting, and physical limitations—may affect a person's ability to perform one or more of the tests.

For that reason, field sobriety tests should never be viewed in isolation. An experienced DUI attorney should carefully review not only the officer's written reports, but also any available body-worn camera footage, dash camera video, and other evidence to determine whether the tests were administered correctly, whether the officer accurately described the driver's performance, and whether other explanations may exist for the observations documented during the investigation.

This guide explains how field sobriety tests are administered in Idaho DUI investigations, the three standardized tests recognized by NHTSA, common mistakes that can affect the reliability of the tests, and how field sobriety test evidence may become an important issue in defending a DUI case.

The Three Standardized Field Sobriety Tests

The National Highway Traffic Safety Administration (NHTSA) recognizes three Standardized Field Sobriety Tests (SFSTs) that are commonly used during DUI investigations throughout the United States, including Idaho. These tests are:

• Horizontal Gaze Nystagmus (HGN)

• Walk-and-Turn (WAT)

• One-Leg Stand (OLS)

These three tests were developed as standardized investigative tools. "Standardized" means that NHTSA has established detailed procedures for how each test should be explained, demonstrated, administered, observed, and scored. Officers receive training on these procedures, and the reliability of the tests depends, in part, on whether they are administered consistently with that training.

The standardized field sobriety tests are not designed to determine a driver's blood alcohol concentration, nor are they intended to establish guilt or innocence. Instead, they are one component of a DUI investigation. Officers may also consider driving behavior, statements made by the driver, physical appearance, the odor of an alcoholic beverage, admissions regarding alcohol or drug consumption, and the results of breath or blood testing when deciding whether probable cause exists to make an arrest.

Each of the three standardized tests attempts to evaluate a different aspect of a person's physical or cognitive functioning:

• Horizontal Gaze Nystagmus (HGN) evaluates involuntary eye movements that may be associated with alcohol impairment or certain medical conditions.

• Walk-and-Turn (WAT) is a divided-attention test intended to assess a person's ability to follow instructions while performing a series of physical tasks.

• One-Leg Stand (OLS) is another divided-attention test designed to evaluate balance, coordination, and the ability to complete multiple tasks simultaneously.

Because these tests require individuals to perform physical and mental tasks under roadside conditions, many factors unrelated to alcohol or drug impairment may influence performance. Age, prior injuries, medical conditions, fatigue, footwear, uneven pavement, weather conditions, lighting, nervousness, and physical disabilities may all affect how a person performs during the tests.

For that reason, field sobriety tests should be evaluated in the context of the entire investigation rather than viewed as conclusive evidence of impairment. In many DUI cases, body-worn camera footage provides an opportunity to compare the officer's written report with the driver's actual performance during the tests. A careful review of the video may reveal details that are not fully reflected in the police reports or may provide additional context for the officer's observations.

The following sections explain each of the three standardized field sobriety tests in greater detail, including how they are administered, what officers are trained to observe, and issues that may affect the reliability or interpretation of the results.

Horizontal Gaze Nystagmus (HGN): How the Test Works, What Officers Look For, and Common Issues

The Horizontal Gaze Nystagmus (HGN) test is usually the first standardized field sobriety test administered during a DUI investigation. Unlike the other standardized field sobriety tests, HGN does not require a person to walk, balance, or perform physical movements. Instead, the officer observes the driver's eyes while directing the driver to follow a moving object—typically a pen, finger, or small flashlight—with only their eyes.

What Is Nystagmus?

Nystagmus is an involuntary jerking or bouncing movement of the eyes. Many people have never heard the term until they are arrested for DUI.

According to NHTSA training materials, alcohol consumption may exaggerate certain types of horizontal gaze nystagmus. Officers are trained to look for specific eye movements that, when combined with other evidence, may contribute to their determination that a driver is impaired.

Importantly, the HGN test is not a test for blood alcohol concentration, nor does it establish that a person is legally under the influence. It is simply one investigative tool used during a DUI investigation.

How Is the Test Administered?

During the test, the officer will usually instruct the driver to:

• Keep their head still.

• Follow the stimulus using only their eyes.

• Continue watching the object until instructed to stop.

The officer slowly moves the stimulus from side to side while observing each eye individually.

Because the test depends on subtle eye movements, proper administration is important. Officers receive training on how to position the stimulus, how quickly to move it, how long to pause at various points, and how to observe each eye separately.

What Are Officers Trained to Look For?

Under NHTSA's standardized procedures, officers are trained to look for three clues in each eye, for a total of six possible clues:

• Lack of smooth pursuit.

• Distinct and sustained nystagmus at maximum deviation.

• Onset of nystagmus prior to approximately 45 degrees.

The officer records which clues they believe were observed and considers those observations together with the remainder of the DUI investigation.

Why Proper Administration Matters

The reliability of the HGN test depends upon proper administration and observation. If standardized procedures are not followed, the value of the test may be affected.

For example, an attorney reviewing a DUI case may examine issues such as:

• Whether the officer gave proper instructions.

• Whether the stimulus was moved appropriately.

• Whether each eye was evaluated separately.

• Whether environmental conditions interfered with the test.

• Whether the officer documented the observations consistently with the body camera video.

These issues may become important when evaluating the overall reliability of the officer's conclusions.

Can Medical Conditions Affect the Test?

Yes.

Numerous medical, neurological, and vision-related conditions may affect eye movements. Certain medications, fatigue, prior injuries, and other medical conditions may also be relevant.

That does not necessarily mean the officer administered the test incorrectly or that the observations are invalid. It does mean that HGN results should always be considered in the context of the entire investigation and, where appropriate, the individual's medical history.

Why Body Camera Video Can Be Important

One of the most valuable pieces of evidence in many Idaho DUI cases is the officer's body-worn camera footage.

Although subtle eye movements themselves are often difficult—or impossible—to evaluate on video, the recording may still provide important information about how the HGN test was administered. The video may show:

• The instructions that were given.

• The driver's cooperation.

• Whether the driver appeared to understand the instructions.

• The positioning of the officer and the driver.

• Lighting conditions.

• Interruptions or distractions during testing.

• Whether the officer followed a consistent testing sequence.

For that reason, body camera footage should be reviewed together with the officer's written report and the remaining evidence rather than relying on the report alone.

HGN Is Only One Part of the Investigation

The HGN test is only one component of a DUI investigation. Officers typically consider HGN together with driving behavior, personal observations, the Walk-and-Turn test, the One-Leg Stand test, statements made by the driver, and any available chemical testing.

No single field sobriety test determines whether a person is guilty of DUI. Every case should be evaluated based on the totality of the circumstances and the available evidence.

The Walk-and-Turn Test (WAT)

The Walk-and-Turn (WAT) is one of the three standardized field sobriety tests recognized by the National Highway Traffic Safety Administration (NHTSA). Unlike the Horizontal Gaze Nystagmus test, which focuses on involuntary eye movements, the Walk-and-Turn is a divided-attention test. It is designed to evaluate a person's ability to listen to instructions, remember those instructions, maintain balance, and perform physical movements at the same time.

According to NHTSA, driving requires a person to divide their attention among multiple tasks simultaneously. The Walk-and-Turn attempts to assess similar abilities by requiring a driver to concentrate on several tasks at once while following a specific sequence of instructions.

How Is the Walk-and-Turn Test Performed?

The officer will typically instruct the driver to:

• Stand with one foot directly in front of the other, heel-to-toe.

• Keep their arms at their sides.

• Maintain that position while the officer explains and demonstrates the test.

• Walk nine heel-to-toe steps along an imaginary or designated straight line.

• Turn using a series of small steps as demonstrated by the officer.

• Return by taking nine heel-to-toe steps back to the starting point.

• Count each step aloud.

• Continue watching their feet while walking.

• Keep their arms at their sides until the test is completed.

The officer generally demonstrates portions of the test before asking the driver to begin.

What Are Officers Trained to Look For?

Under NHTSA's standardized procedures, officers are trained to observe eight possible clues during the Walk-and-Turn test:

• Cannot keep balance during the instructional phase.

• Starts the test before being instructed to begin.

• Stops while walking.

• Does not touch heel-to-toe.

• Steps off the line.

• Uses arms for balance.

• Makes an improper turn.

• Takes an incorrect number of steps.

The officer records the clues they believe they observed and considers those observations together with the remainder of the DUI investigation.

Why Standardized Instructions Matter

The Walk-and-Turn test is intended to be administered using standardized procedures developed by NHTSA. Proper instructions, demonstrations, and scoring procedures help promote consistency from one investigation to another.

Because the test depends on following multiple instructions, an attorney reviewing the case may examine issues such as:

• Whether the officer clearly explained the test.

• Whether the officer properly demonstrated the turning procedure.

• Whether the driver indicated they understood the instructions.

• Whether interruptions occurred during the instructional phase.

• Whether the officer scored the test consistently with the driver's actual performance shown on body camera footage.

Even relatively small deviations from standardized procedures may become relevant when evaluating the significance of the officer's observations.

Can Someone Perform Poorly Without Being Impaired?

Yes.

The Walk-and-Turn test requires coordination, balance, concentration, and the ability to remember several instructions simultaneously. Numerous factors unrelated to alcohol or drug impairment may affect performance, including:

• Knee, hip, ankle, or back injuries.

• Balance disorders or vertigo.

• Advanced age.

• Obesity or other mobility limitations.

• Uneven pavement or gravel.

• Sloped roadways.

• Poor lighting.

• Heavy traffic or roadside distractions.

• Inappropriate footwear, including high heels, work boots, flip-flops, or shoes with poor traction.

• Nervousness or anxiety during a traffic stop.

Because these conditions may influence performance, officers are trained to ask certain medical screening questions before administering the standardized field sobriety tests. The answers to those questions—and whether they were documented accurately—may become important issues during a later review of the case.

Why Body Camera Video Matters

The officer's written report typically summarizes the clues observed during the Walk-and-Turn test. However, body-worn camera footage often provides a much more complete picture of what actually occurred.

Video may help document:

• The surface on which the test was performed.

• Weather and lighting conditions.

• Whether the officer gave complete instructions.

• Whether the driver appeared confused or simply nervous.

• How closely the driver's performance matched the officer's written description.

• Whether environmental conditions affected the driver's balance or ability to complete the test.

A careful review of the video may identify details that are difficult to capture in a written report alone.

The Walk-and-Turn Test Is Only One Piece of the Investigation

Like the other standardized field sobriety tests, the Walk-and-Turn does not determine whether a person is guilty of DUI. Instead, it is one investigative tool considered together with the officer's observations, driving behavior, statements made during the encounter, and any chemical test results.

For that reason, the Walk-and-Turn should always be evaluated as part of the entire DUI investigation rather than viewed in isolation.

The One-Leg Stand Test (OLS)

The One-Leg Stand (OLS) is the third standardized field sobriety test recognized by the National Highway Traffic Safety Administration (NHTSA). Like the Walk-and-Turn test, it is considered a divided-attention test, meaning it is designed to evaluate a person's ability to perform physical and mental tasks simultaneously.

The One-Leg Stand requires a driver to maintain balance while following a series of instructions and performing a simple counting exercise. According to NHTSA, the test is intended to assess a person's ability to divide attention among multiple tasks, which officers are trained to consider as one factor during a DUI investigation.

How Is the One-Leg Stand Test Performed?

The officer will typically instruct the driver to:

• Stand with both feet together.

• Keep their arms at their sides.

• Raise one foot approximately six inches off the ground.

• Keep the raised foot parallel to the ground.

• Look at the raised foot.

• Count aloud using the officer's instructions until told to stop.

The officer generally demonstrates the test before asking the driver to perform it.

Unlike the Walk-and-Turn test, the One-Leg Stand is stationary. Even so, it requires balance, coordination, concentration, and the ability to follow instructions while performing multiple tasks at the same time.

What Are Officers Trained to Look For?

Under NHTSA's standardized procedures, officers are trained to observe four possible clues during the One-Leg Stand test:

• Swaying while balancing.

• Using the arms for balance.

• Hopping.

• Putting the raised foot down before the test is completed.

The officer records the clues they believe they observed and considers those observations together with the other evidence collected during the investigation.

Why Proper Administration Is Important

As with the other standardized field sobriety tests, the One-Leg Stand is intended to be administered according to standardized NHTSA procedures.

An attorney reviewing the investigation may examine questions such as:

• Did the officer clearly explain and demonstrate the test?

• Did the driver indicate that the instructions were understood?

• Was the test performed on a reasonably suitable surface?

• Were weather, lighting, or traffic conditions appropriate?

• Was the officer's scoring consistent with the body camera footage?

The reliability of the observations depends, in part, on whether standardized procedures were followed.

Can Physical Conditions Affect Performance?

Yes.

Many individuals who are completely sober may have difficulty standing on one leg for an extended period of time.

Factors that may affect performance include:

• Knee, ankle, hip, or back injuries.

• Arthritis.

• Inner ear or balance disorders.

• Neurological conditions.

• Obesity.

• Advanced age.

• Fatigue.

• Certain medications.

• Poor footwear.

• Uneven, sloped, or slippery pavement.

• Wind, rain, snow, or other weather conditions.

Because these and other conditions may influence a person's balance, officers are trained to ask questions about medical conditions and physical limitations before administering standardized field sobriety tests. Those responses, together with the body camera footage and the officer's written report, may become important when evaluating the significance of the test results.

Why Video Review Is Important

Body-worn camera footage often provides valuable context for the One-Leg Stand test.

The recording may show:

• The actual testing location.

• Road and weather conditions.

• Whether the officer properly explained the test.

• The driver's balance and coordination.

• Whether the officer's written report accurately reflects the driver's performance.

Although a written report summarizes the officer's observations, the video frequently provides a more complete picture of the circumstances under which the test was administered.

The One-Leg Stand Is Not a Pass-or-Fail Test

The One-Leg Stand does not determine whether someone is guilty of DUI.

Instead, it is one component of the officer's overall investigation. Officers consider the results of the One-Leg Stand together with the Horizontal Gaze Nystagmus test, the Walk-and-Turn test, driving behavior, personal observations, statements made by the driver, and any available chemical testing.

No single field sobriety test, standing alone, determines whether a driver is impaired. Every DUI case should be evaluated based on the totality of the evidence and the specific facts surrounding the investigation.

Are Field Sobriety Tests Scientifically Reliable?

One of the most common questions people ask after a DUI arrest is whether field sobriety tests are scientifically reliable. The answer is more nuanced than a simple "yes" or "no."

The three standardized field sobriety tests were developed by the National Highway Traffic Safety Administration (NHTSA) as investigative tools to assist law enforcement officers during DUI investigations. NHTSA has conducted research evaluating the standardized tests when they are administered under controlled conditions by properly trained officers using standardized procedures.

At the same time, it is important to understand what the standardized field sobriety tests are—and what they are not.

They Are Investigative Tools

The standardized field sobriety tests are designed to help officers determine whether they have probable cause to believe a driver is impaired and whether additional investigation or an arrest may be appropriate.

They are not designed to directly measure a person's blood alcohol concentration, nor do they determine whether someone is legally guilty of DUI.

Instead, they are one part of the overall investigation.

Standardization Is Important

The term "standardized" is significant.

NHTSA developed detailed procedures governing how the Horizontal Gaze Nystagmus, Walk-and-Turn, and One-Leg Stand tests should be explained, demonstrated, administered, observed, and scored.

The validation studies conducted by NHTSA were based upon those standardized procedures.

If the tests are administered differently than they were designed to be administered, questions may arise regarding the significance of the officer's observations.

Performance May Be Influenced by Many Factors

Even when standardized procedures are followed, field sobriety test performance may be affected by factors unrelated to alcohol or drug impairment.

Examples include:

• Age.

• Prior injuries.

• Medical conditions.

• Balance disorders.

• Neurological conditions.

• Fatigue.

• Anxiety.

• Physical disabilities.

• Obesity.

• Weather conditions.

• Uneven pavement.

• Poor lighting.

• Inappropriate footwear.

These factors do not necessarily invalidate the tests. However, they may provide important context when evaluating a driver's performance and the officer's conclusions.

The Entire Investigation Matters

Field sobriety tests are only one component of a DUI investigation.

Officers also consider many other factors, including:

• Driving behavior.

• Personal observations.

• Statements made by the driver.

• The odor of an alcoholic beverage or other substances.

• Physical appearance.

• Chemical test results, when available.

• Other evidence gathered during the investigation.

Likewise, attorneys evaluating a DUI case consider all of the available evidence rather than focusing on any single field sobriety test.

Why Video Evidence Is Often Important

Body-worn camera and dash camera recordings have become an increasingly important part of DUI investigations.

Video evidence may allow an attorney, prosecutor, judge, or jury to observe many aspects of the testing process firsthand, including:

• Whether the officer properly explained the tests.

• The conditions under which the tests were administered.

• The driver's actual performance.

• Whether the officer's written report accurately reflects what occurred.

Although a video recording may not capture every detail—particularly subtle observations such as eye movements during the Horizontal Gaze Nystagmus test—it often provides valuable context that cannot be conveyed fully in a written report alone.

Every Case Is Different

No two DUI investigations are exactly alike.

The significance of field sobriety tests depends upon the totality of the circumstances, including how the tests were administered, the surrounding conditions, the driver's physical condition, and the remaining evidence collected during the investigation.

For that reason, field sobriety tests should not be viewed in isolation. Instead, they should be evaluated as one part of the complete factual and legal picture presented in each individual DUI case.

Are Field Sobriety Tests Required in Idaho?

One of the most important distinctions in an Idaho DUI investigation is the difference between field sobriety tests and evidentiary alcohol or drug testing.

The Horizontal Gaze Nystagmus, Walk-and-Turn, and One-Leg Stand tests are roadside investigative tools used by officers to help determine whether there is probable cause to make a DUI arrest. They are different from an evidentiary breath test or blood test requested under Idaho's implied-consent laws.

Can You Refuse Field Sobriety Tests in Idaho?

A driver can decline to participate in field sobriety testing. Refusing field sobriety tests, however, is not necessarily consequence-free.

Unlike refusal of evidentiary testing, declining roadside field sobriety tests does not by itself trigger the driver's license suspension procedures associated with refusing an evidentiary breath or blood test. Nevertheless, an officer may consider the refusal together with the other circumstances of the investigation when deciding whether probable cause exists to make an arrest.

Idaho courts have also recognized that a person's refusal to participate in field sobriety testing may, depending on the circumstances, be relevant evidence in a DUI case. For that reason, the issue is more complicated than simply saying that a driver has nothing to lose by refusing the tests.

Field Sobriety Tests Are Different From Evidentiary Testing

This distinction is important because people frequently use the terms "breathalyzer," "breath test," and "field sobriety test" interchangeably even though they may involve very different legal consequences.

Field sobriety tests generally include:

• Horizontal Gaze Nystagmus;

• Walk-and-Turn;

• One-Leg Stand; and

• In some investigations, additional non-standardized or drug-impairment tests.

Evidentiary testing may include:

• An evidentiary breath alcohol test; or

• A blood test for alcohol or drugs.

Idaho's implied-consent laws impose separate consequences for refusing certain evidentiary testing. Those consequences should not be confused with a decision not to perform roadside field sobriety exercises.

Can an Officer Still Arrest Someone Who Refuses the Tests?

Yes.

An officer does not need a completed set of field sobriety tests in every case before making a DUI arrest. Probable cause is evaluated from the totality of the circumstances.

Depending upon the particular investigation, an officer may rely on evidence such as:

• Driving behavior;

• The circumstances of the traffic stop;

• Odor of an alcoholic beverage;

• Statements or admissions regarding alcohol or drug use;

• Speech;

• Coordination or balance;

• Physical appearance;

• Observations made while the driver retrieves documents or exits the vehicle;

• A refusal or inability to perform field sobriety tests; and

• Other information available to the officer.

The absence of field sobriety test results therefore does not necessarily prevent an arrest or DUI prosecution.

Why the Distinction Matters

A person arrested for DUI may later remember telling the officer, "I refused the breath test," when the person actually declined a roadside breath test, refused field sobriety exercises, or refused an evidentiary breath test after arrest. Those events can carry very different legal consequences.

For that reason, an attorney reviewing a DUI investigation should determine exactly which tests were requested, when they were requested, what instructions or warnings were given, how the driver responded, and what happened afterward.

Body-worn camera footage is often particularly useful in resolving these questions because it may show precisely what the officer requested and how the driver responded.

Non-Standardized and Optional Field Sobriety Tests

In addition to the three standardized field sobriety tests—Horizontal Gaze Nystagmus, Walk-and-Turn, and One-Leg Stand—an officer conducting a DUI investigation may ask a driver to perform other roadside exercises.

These are sometimes referred to as non-standardized or optional field sobriety tests. They may provide an officer with additional observations about a driver's ability to understand instructions, divide attention, maintain balance, estimate time, or perform other physical and mental tasks.

Importantly, these exercises should not be confused with the three NHTSA Standardized Field Sobriety Tests. The fact that an officer uses an additional exercise does not make that exercise part of the standardized three-test SFST battery.

Idaho State Police procedure currently identifies several optional tests that a trooper may administer when the trooper believes doing so is appropriate.

Alphabet Recitation

An officer may ask a driver to recite part or all of the alphabet.

Depending upon the instructions, the driver may be asked to begin with a particular letter, stop at another letter, or simply recite the alphabet without singing it.

The officer may observe whether the person:

• Understands the instructions;

• Begins and stops at the requested letters;

• Skips or repeats letters;

• Loses their place;

• Requires the instructions to be repeated; or

• Otherwise has difficulty completing the task.

Difficulty performing an alphabet exercise does not necessarily establish impairment. English proficiency, education, anxiety, hearing difficulties, learning disabilities, distraction, and simple misunderstanding of the instructions may affect performance.

Counting Exercises

An officer may ask a driver to count forward or backward between specified numbers.

For example, the person might be instructed to begin at one number and stop at another rather than simply count indefinitely.

This type of exercise allows the officer to observe whether the person can understand, remember, and follow a sequence of instructions while performing a mental task.

An attorney reviewing the test should consider not only whether mistakes occurred, but also whether the instructions were clear and whether there may be reasonable explanations unrelated to impairment.

Finger Dexterity or Finger Count

A finger-dexterity exercise generally requires the person to touch the tip of the thumb to the fingers in a particular sequence while counting aloud.

The exercise may require the person to move from one finger to another and then reverse the sequence.

An officer may observe:

• Whether the instructions were understood;

• Whether the correct fingers were touched;

• Whether the proper sequence was followed;

• Whether the person counted correctly; and

• Whether coordination appeared impaired.

As with other optional exercises, performance can be affected by circumstances having nothing to do with alcohol or drug use, including hand injuries, arthritis, neurological conditions, unfamiliarity with the exercise, and anxiety.

Modified Romberg Balance Test

The Modified Romberg Balance test differs significantly from the Walk-and-Turn and One-Leg Stand.

Although the precise instructions may vary depending upon the officer's training, the person is generally asked to stand in a stationary position, close their eyes, tilt their head back, and estimate the passage of a specified amount of time.

The exercise may allow an officer to observe several things at once, including:

• Balance;

• Body sway;

• Ability to follow instructions;

• Ability to estimate the passage of time; and

• Other physical observations.

The Modified Romberg test may be particularly relevant in investigations involving suspected drug impairment because certain substances or medical conditions may affect a person's perception of time, balance, or other physiological functions.

However, performance may also be affected by anxiety, fatigue, balance disorders, inner-ear conditions, neurological issues, environmental conditions, and the person's understanding of the instructions.

Lack of Convergence

Lack of Convergence, sometimes abbreviated as LOC, is an eye-related observation that may be used during certain impairment investigations.

During a convergence evaluation, the officer generally moves a stimulus toward the bridge of the person's nose and observes whether both eyes are able to move inward toward the stimulus.

An inability of the eyes to converge may be one observation considered during an investigation, particularly when drug impairment is suspected.

As with HGN, eye-related observations should be evaluated cautiously and in context. Vision problems, neurological conditions, eye disorders, medications, injuries, and other factors may potentially affect eye movement.

Finger-to-Nose Evaluation

Officers with additional Advanced Roadside Impaired Driving Enforcement, or ARIDE, training may also use a Finger-to-Nose evaluation.

During this exercise, the person is generally instructed to close their eyes, tilt their head back, extend their arms, and touch the tip of the nose with a specified finger when directed.

The officer may observe such things as:

• Ability to follow the instructions;

• Balance;

• Whether the correct hand is used;

• Whether the fingertip accurately touches the tip of the nose; and

• Other physical observations associated with the exercise.

Finger-to-Nose testing is commonly associated with more advanced drug-impairment investigations and should not be confused with the three standardized roadside SFSTs.

Why the Difference Between Standardized and Optional Tests Matters

The distinction between standardized and optional field sobriety tests is important.

NHTSA's standardized SFST battery consists of only three tests:

• Horizontal Gaze Nystagmus;

• Walk-and-Turn; and

• One-Leg Stand.

Those tests were selected and studied as a standardized three-test battery. Other roadside exercises may provide observations that an officer considers useful, but they have not been validated by NHTSA in the same manner as the standardized three-test battery.

That does not automatically make an optional exercise meaningless or inadmissible. It does mean that its significance should be evaluated differently.

When reviewing an optional field sobriety test, important questions may include:

• What exactly was the driver instructed to do?

• Were the instructions clear and complete?

• Was the exercise administered consistently with the officer's training?

• Did the driver understand the instructions?

• What specific observations did the officer make?

• Are those observations visible on body camera footage?

• Could medical, physical, language, environmental, or other factors explain the driver's performance?

• How much weight should the exercise reasonably receive when considered with the rest of the evidence?

Optional Tests Should Be Considered in Context

One of the problems with discussing field sobriety testing in general terms is that a police report may reduce an extended roadside interaction to a few sentences describing what the officer considered mistakes.

The actual interaction can be considerably more complicated.

A driver may perform portions of an exercise correctly and make mistakes on others. Instructions may be misunderstood. An officer may repeat or modify instructions. Environmental distractions may occur. A person may have physical or medical limitations that are not readily apparent from the written report.

For that reason, optional field sobriety exercises—like the standardized tests—should be evaluated in the context of the entire investigation.

Whenever available, the police reports should be compared with body-worn camera and dash-camera footage to determine what instructions were actually given, how the driver actually performed, and whether the officer's characterization of the exercise fairly reflects what occurred.

Common Mistakes and Problems in Field Sobriety Testing

Field sobriety testing is intended to be standardized. That means the tests are not simply general balance or coordination exercises that an officer can administer however the officer chooses. NHTSA training establishes specific instructions, demonstrations, procedures, clues, and scoring criteria for the Horizontal Gaze Nystagmus, Walk-and-Turn, and One-Leg Stand tests.

That does not mean that every departure from training automatically makes a field sobriety test meaningless or legally inadmissible. It does mean that the way a test was actually administered matters when evaluating the significance of the officer's conclusions.

A careful DUI investigation review should therefore ask two separate questions:

1. What did the driver actually do?

2. Was the test administered and scored in the manner contemplated by the officer's training?

Those questions are particularly important now that body-worn camera video frequently allows the officer's written description to be compared with what actually occurred at roadside.

Incomplete or Confusing Instructions

Field sobriety tests require the subject to perform unfamiliar tasks while following detailed instructions, often late at night, alongside a roadway, with emergency lights flashing and traffic nearby.

Clear instructions are therefore important.

For example, during the Walk-and-Turn test, NHTSA training calls for the officer to explain and demonstrate the heel-to-toe stance, tell the person not to begin until instructed, explain the nine heel-to-toe steps, demonstrate the turn, instruct the person to return with nine heel-to-toe steps, count aloud, watch their feet, keep their arms at their sides, and continue walking once the test begins.

If an instruction was never given, it may be problematic to treat the person's failure to follow that instruction as evidence of impairment.

One particularly good example involves the Walk-and-Turn clue commonly described as "starts too soon." An officer should not score that clue merely because a person begins walking before the officer expected. The instruction not to begin until told to do so must first have been communicated.

The same principle applies throughout field sobriety testing: the driver's performance should be evaluated against the instructions the driver was actually given.

Treating Normal Behavior as a Scorable Clue

Another issue can arise when an officer describes behavior as a "clue" even though it does not satisfy the standardized scoring criteria.

The Walk-and-Turn provides several examples.

Heel-to-Toe

A person does not necessarily receive a Walk-and-Turn clue simply because the heel and toe fail to make perfect contact.

Under NHTSA training, the "does not touch heel-to-toe" clue is scored when the person leaves a gap of more than approximately one-half inch between the heel and toe.

That distinction can matter.

A police report may state generally that a driver "failed to walk heel-to-toe," while the video may show that the person came very close on nearly every step. A careful review should determine whether the actual performance meets the officer's standardized scoring criteria rather than simply accepting a generalized description.

Balance During the Instructional Position

Similarly, merely swaying while standing in the heel-to-toe instructional position is not necessarily the Walk-and-Turn clue of being unable to maintain balance during instructions.

NHTSA training distinguishes ordinary movement from actually breaking the heel-to-toe stance. The relevant clue involves the feet separating or the person stepping away from the position.

That difference can be difficult to appreciate from a short written report but may be apparent on video.

Incorrect HGN Administration

Horizontal Gaze Nystagmus is especially dependent upon proper administration because the officer is attempting to observe relatively subtle eye movements.

NHTSA training contains detailed procedures governing the location and movement of the stimulus.

Among other things, the officer is trained to position the stimulus approximately 12 to 15 inches from the person's nose and slightly above eye level. The officer performs preliminary checks, including equal pupil size, resting nystagmus, and equal tracking, before evaluating the standardized HGN clues.

Different portions of the examination also require different stimulus movements and timing.

For example, the officer is trained to move the stimulus smoothly when evaluating smooth pursuit, hold the eye at maximum deviation for a specified period, and move the stimulus relatively slowly when determining whether the onset of nystagmus occurs before approximately 45 degrees.

Potential issues may therefore include:

• Holding the stimulus too close to or too far from the face;

• Moving the stimulus too quickly;

• Failing to hold the eye long enough at maximum deviation;

• Failing to check both eyes separately;

• Failing to perform the preliminary eye checks;

• Positioning the stimulus incorrectly;

• Conducting the test where flashing lights or other visual distractions may interfere;

• Failing to investigate an apparent difference between the eyes; or

• Describing conclusions in the report without adequately documenting how the test was performed.

HGN is also difficult to evaluate from ordinary body-camera footage because the camera frequently does not provide a sufficiently close or stable view of the eyes. Video may nevertheless reveal whether the officer followed the general administration sequence and timing.

Problems With the Walk-and-Turn Surface or Location

The Walk-and-Turn is intended to evaluate a person's ability to maintain a heel-to-toe position, walk a straight line, turn in a prescribed manner, and return.

The testing environment therefore matters.

Potential concerns may arise when the test is conducted on:

• Gravel;

• Broken or uneven pavement;

• A substantial slope;

• A roadway shoulder;

• Wet or icy pavement;

• Loose dirt;

• An area with obstructions;

• A location immediately adjacent to moving traffic; or

• Another surface that makes balance or precise foot placement more difficult.

The mere existence of an imperfect surface does not necessarily make the test useless. Roadside testing rarely occurs under laboratory conditions.

The proper inquiry is whether the particular conditions reasonably affected the person's ability to perform the tasks and whether those conditions were taken into account when the officer interpreted the results.

Body-camera footage can be particularly valuable in answering that question.

Problems With the Walk-and-Turn Demonstration

The turn used in the Walk-and-Turn is not an ordinary turn.

The subject is instructed to leave the front foot on the line and use the other foot to take a series of small steps around it before returning in the opposite direction.

Because most people would not naturally turn in that manner, the officer's demonstration matters.

If a person performs a different turn, a reviewer should consider:

• What did the officer actually demonstrate?

• Could the driver see the demonstration?

• Were the instructions interrupted?

• Did the driver indicate confusion?

• Did the officer clarify the instructions before the test began?

A person can understand "walk nine steps, turn, and walk back" while still misunderstanding the very specific turning maneuver the standardized test requires.

Incorrect One-Leg Stand Instructions

The One-Leg Stand also requires a specific procedure.

NHTSA training instructs the person to raise one foot approximately six inches from the ground, keep the raised foot parallel to the ground, keep both legs straight, look at the elevated foot, keep the arms at the sides, and count aloud in a prescribed manner until told to stop.

The officer is responsible for timing approximately 30 seconds.

Potential problems may include:

• Telling the person to lift the leg substantially higher than instructed;

• Demonstrating the test with a bent knee;

• Failing to instruct the person to keep both legs straight;

• Failing to tell the person to look at the elevated foot;

• Ending the test significantly early;

• Allowing the test to continue substantially beyond the prescribed period;

• Failing to explain the required counting method; or

• Scoring ordinary movements as clues when they do not satisfy NHTSA's criteria.

For example, the standardized clue for using the arms for balance involves moving one or both arms approximately six inches or more away from the side of the body. A slight natural movement of the hands or arms is not necessarily the standardized clue.

Likewise, if a person puts a foot down during the test, NHTSA training calls for the officer to instruct the person to raise the foot again and continue counting from the point where the foot touched the ground.

Failing to Account for Physical Limitations

Before drawing conclusions from physical performance, an officer should consider whether the person has conditions that could affect balance, coordination, vision, or mobility.

Potentially relevant factors include:

• Knee injuries;

• Hip injuries;

• Ankle injuries;

• Back problems;

• Neurological conditions;

• Inner-ear or balance disorders;

• Arthritis;

• Recent surgery;

• Vision problems;

• Prosthetic devices;

• Physical disabilities; and

• Other medical limitations.

A person may also tell an officer about a physical condition before testing begins.

That statement should not simply disappear from the analysis.

If a driver tells an officer, for example, that a knee injury makes standing on one leg difficult, the subsequent inability to perform the One-Leg Stand should be evaluated in light of that information rather than automatically attributed to alcohol impairment.

Footwear Can Matter

Footwear can also affect roadside performance.

High heels, sandals, flip-flops, heavy work boots, loose shoes, damaged footwear, or other unusual shoes may make heel-to-toe walking or standing on one leg more difficult.

The issue is not whether footwear provides an automatic excuse for poor performance. The issue is whether the conditions under which the person performed the test provide a reasonable alternative explanation for what the officer observed.

Video evidence frequently answers this question better than a written report.

Giving Multiple or Changing Instructions During the Test

Another issue can arise when an officer changes, supplements, or repeatedly interrupts the instructions after a test has begun.

Not every reminder is improper.

For example, NHTSA training specifically contemplates reminding a person during the Walk-and-Turn to continue counting aloud or watching their feet if they stop doing so. Such a reminder does not, by itself, invalidate the test.

The important distinction is between a legitimate reminder and instructions that materially change the test or create confusion about what the person is expected to do.

When reviewing video, it can be useful to ask whether the driver appears unable to follow a clear instruction or whether the officer and driver are simply communicating poorly.

Scoring the Same Behavior More Than the Standardized Criteria Permit

Field sobriety tests use defined clues rather than an unlimited tally of every perceived mistake.

A person might miss heel-to-toe several times during the Walk-and-Turn, for example, but the standardized scoring system treats "does not touch heel-to-toe" as one category of clue rather than converting each missed step into a new standardized clue.

The frequency of an observation may still be relevant and can appropriately be documented in an officer's narrative. But the number of individual mistakes should not be confused with the number of standardized clues.

Understanding that distinction can be important when a police report makes a test performance sound substantially worse than the standardized scoring actually indicates.

Focusing Only on Mistakes and Ignoring Correct Performance

Police reports understandably tend to document observations the officer believes support an arrest decision.

That can create an incomplete picture.

A report might state that a driver:

• Used an arm for balance;

• Missed heel-to-toe;

• Swayed; and

• Put a foot down.

The report may not emphasize that the same person:

• Understood lengthy instructions;

• Counted correctly;

• Took the correct number of steps;

• Stayed on the line;

• Made the proper turn;

• Followed instructions throughout most of the investigation; or

• Demonstrated normal speech and communication.

Correct performance does not erase properly observed clues. But the entire performance matters when deciding how persuasive the evidence of impairment actually is.

Differences Between the Police Report and the Video

Perhaps the most important development in modern DUI defense is the widespread availability of body-worn camera footage.

Before body cameras, an attorney frequently had little more than the officer's written description of the roadside investigation.

Today, video may allow the defense to examine the interaction in real time.

Sometimes the video strongly confirms the report.

In other cases, the description in the report may make the driver's performance sound substantially worse than it appears on video.

Examples may include:

• A report describing significant balance problems when the video shows only minor movement;

• A report stating that a driver failed to follow instructions when the instructions themselves were unclear;

• A description of poor coordination that is difficult to reconcile with the person's other movements;

• An officer scoring a clue that does not appear to satisfy the standardized criteria; or

• Environmental or physical circumstances visible on video but not mentioned in the report.

The opposite can also occur: video may reveal impairment more clearly than the written report conveys.

For that reason, video should not be approached with a predetermined conclusion. It should be compared objectively with the officer's documentation.

A Mistake Does Not Automatically Defeat the Test

It is important not to overstate the significance of an officer's departure from standardized procedures.

A minor deviation does not automatically cause a DUI case to be dismissed, nor does every imperfectly administered test become worthless.

Instead, the relevant questions are:

• What procedure was supposed to be followed?

• What procedure was actually followed?

• How significant was the difference?

• Could the difference have affected the person's performance or the officer's interpretation?

• Does the remaining evidence independently support the officer's conclusions?

Field sobriety testing is evidence, not a verdict.

The proper defense analysis considers both the strengths and weaknesses of that evidence and places the test results within the context of the entire DUI investigation.

Medical and Physical Conditions That Can Affect Field Sobriety Test Performance

Field sobriety tests require a person to perform tasks involving balance, coordination, vision, concentration, and the ability to follow instructions. Because of that, physical or medical conditions unrelated to alcohol or drug impairment may affect performance.

The existence of a medical condition does not automatically invalidate a field sobriety test, nor does it necessarily explain every observed clue. But it can be an important part of determining how much weight should reasonably be given to the test results.

A careful review should consider what the officer knew about the driver's physical condition before testing began, what questions the officer asked, what the driver reported, and whether the alleged problems observed during testing are consistent with the person's known limitations.

Knee, Ankle, Hip, and Leg Problems

The Walk-and-Turn and One-Leg Stand place obvious demands on the lower body.

A person with a prior knee injury, ankle injury, hip problem, arthritis, joint replacement, chronic pain, or reduced mobility may have difficulty:

• Maintaining a heel-to-toe stance;

• Walking heel-to-toe;

• Making the prescribed Walk-and-Turn maneuver;

• Standing on one leg;

• Keeping both legs straight during the One-Leg Stand; or

• Maintaining balance for the required period.

This issue can be particularly important when a driver tells the officer about an injury before the test begins.

For example, if a person tells an officer that they have a bad knee and then struggles during the One-Leg Stand, the knee condition is relevant when interpreting the performance. It does not necessarily prove that the person was unimpaired, but it provides a potential explanation for difficulties that might otherwise be attributed to alcohol or drugs.

An attorney reviewing the case should compare the person's reported limitation with the actual behavior shown on video. A knee problem that affects standing on one leg may have little relevance to speech, eye movements, or other evidence, while it may have substantial relevance to a balance-based test.

Back Problems

Back injuries and chronic back pain can also affect field sobriety testing.

The Walk-and-Turn requires a person to maintain an unusual heel-to-toe stance, walk precisely along a line, turn using a particular method, and return the same way. The One-Leg Stand shifts much of the person's weight onto a single leg.

For someone with a significant back condition, those movements may cause pain, instability, stiffness, or difficulty maintaining balance.

NHTSA's own refresher materials note that the original research identified people with back problems among those who may experience difficulty with the Walk-and-Turn and One-Leg Stand.

Relevant evidence may include:

• Statements made to the officer before testing;

• Medical records;

• Prior surgeries;

• Physical therapy history;

• Visible braces or assistive devices; and

• The person's movements before and after the field sobriety tests.

How someone walks naturally while approaching the officer, retrieving documents, or returning to a vehicle may provide useful context when evaluating performance during a deliberately difficult balancing exercise.

Inner-Ear and Balance Disorders

Balance depends upon several systems working together, including vision, the inner ear, and sensory information from the muscles and joints.

Conditions affecting the vestibular system or inner ear can therefore influence balance.

Potentially relevant conditions may include:

• Vertigo;

• Ménière's disease;

• Vestibular disorders;

• Ear infections;

• Prior inner-ear injuries; and

• Other conditions affecting equilibrium.

NHTSA training materials specifically identify inner-ear problems as a factor that may make the Walk-and-Turn or One-Leg Stand more difficult.

A balance disorder can be especially significant because two of the three standardized tests—the Walk-and-Turn and One-Leg Stand—depend heavily on balance.

Neurological Conditions

Neurological conditions may affect coordination, balance, eye movement, speech, fine motor skills, or a person's ability to process instructions.

Examples may include:

• Neuropathy;

• Parkinson's disease;

• Multiple sclerosis;

• Prior stroke;

• Traumatic brain injury;

• Tremor disorders;

• Seizure disorders;

• Cerebellar conditions; and

• Other neurological impairments.

The significance of any particular condition depends on the individual and the specific test being evaluated.

A neurological condition affecting gait may be important to the Walk-and-Turn but have little bearing on whether the officer properly observed an HGN clue. Another condition may potentially affect eye movements and become particularly relevant to HGN.

The analysis should therefore be specific rather than simply assuming that a medical diagnosis either explains everything or explains nothing.

Vision and Eye Conditions

Vision-related issues can be particularly important when evaluating Horizontal Gaze Nystagmus.

NHTSA training requires officers to perform preliminary eye checks before evaluating the standardized HGN clues. These include checking pupil size, resting nystagmus, and equal tracking.

An apparent difference between the eyes may warrant further consideration rather than simply being treated as an alcohol-related clue.

Potentially relevant circumstances may include:

• Prior eye surgery;

• Strabismus;

• Significant differences in vision between the eyes;

• Neurological eye disorders;

• Nystagmus caused by conditions unrelated to alcohol;

• Eye injuries; and

• Certain medications or medical conditions affecting eye movement.

NHTSA's current proficiency materials also instruct officers to have the subject remove eyeglasses during HGN testing.

The fact that a person normally wears corrective lenses should not itself be interpreted as evidence of impairment. The important question is whether the officer's observations were made and interpreted appropriately given the individual's actual eye condition.

Age

Age may be relevant to physical field sobriety testing.

NHTSA's refresher materials note that the original standardized field sobriety test research suggested that individuals over age 65 may experience greater difficulty with some balance-based tests.

That does not mean every person over 65 is incapable of performing the tests, and it does not create an automatic exclusion from testing.

It does mean that age should be considered as part of the total circumstances rather than ignored.

Physical ability varies considerably from person to person. A physically active 70-year-old may perform better than a much younger individual with orthopedic or balance problems.

The proper analysis focuses on the actual person, not merely an age category.

Body Size and Physical Conditioning

Body size, mobility, strength, and physical conditioning may also affect some roadside exercises.

NHTSA's refresher materials discuss the original research concerning body weight and the One-Leg Stand, while also acknowledging limitations in the underlying weight data.

For purposes of evaluating an actual DUI case, the more useful question is usually not whether a person falls into a particular weight category.

Instead, the question is:

Did this particular person's physical condition reasonably affect their ability to perform this particular task?

A person may have difficulty standing on one leg because of body mechanics, mobility limitations, an old injury, lack of physical conditioning, or some combination of factors.

Those circumstances should be evaluated along with the remainder of the evidence.

Fatigue

Fatigue can affect concentration, coordination, reaction time, and balance.

Many DUI arrests occur late at night or early in the morning. A person may have:

• Worked a long shift;

• Driven for many hours;

• Been awake unusually long;

• Been awakened shortly before the encounter; or

• Been physically exhausted for reasons unrelated to alcohol or drug consumption.

Fatigue does not necessarily explain poor field sobriety performance, particularly where there is substantial additional evidence of impairment.

But it may be relevant when evaluating relatively minor mistakes on divided-attention exercises.

Anxiety and the Stress of a Traffic Stop

Field sobriety tests are normally performed under circumstances very different from an ordinary balance exercise.

The person may be:

• Standing next to a roadway;

• Surrounded by police officers;

• Illuminated by emergency lights;

• Worried about being arrested;

• Conscious of passing motorists;

• Being recorded by body cameras;

• Trying to remember multiple unfamiliar instructions; and

• Concerned about what will happen next.

Anxiety can affect concentration and communication and may cause trembling, stiffness, rushed movements, or difficulty processing instructions.

It would be incorrect to assume that every sign of nervousness is unrelated to impairment. It would be equally incorrect to assume that nervous behavior during a DUI investigation can only be explained by alcohol or drugs.

The circumstances should be evaluated objectively.

Medications and Medical Treatment

Prescription and over-the-counter medications may also become relevant.

Some medications can affect balance, coordination, alertness, vision, or eye movement. Others may have no meaningful effect on field sobriety performance.

The fact that someone takes medication does not itself establish either impairment or innocence.

A proper evaluation may require determining:

• What medication was taken;

• When it was taken;

• The prescribed dosage;

• Whether the person had taken it previously;

• Whether the medication is known to affect coordination or balance; and

• Whether toxicological evidence is consistent with the officer's observations.

Medical explanations should be evaluated on evidence rather than assumption.

Medical Conditions Should Be Documented Before Testing When Possible

One of the most important parts of reviewing field sobriety testing is determining what the officer knew before the tests were administered.

If the body-camera recording shows the driver saying:

"I have had three knee surgeries and can't stand on my right leg,"

that statement may substantially change how later One-Leg Stand performance should be interpreted.

Likewise, if the officer asks whether the person has any medical problems and the driver expressly denies having any, that fact may also be relevant.

A thorough evaluation should therefore review the entire interaction rather than beginning the analysis only when the first test starts.

Compare Test Performance With the Person's Other Movements

Another useful form of analysis is to compare performance during the standardized exercises with the person's ordinary movements throughout the encounter.

For example:

• How did the person exit the vehicle?

• Did they walk normally to the testing location?

• Did they stumble when they were not performing a test?

• Could they retrieve a license and registration?

• Did they stand normally during conversation?

• How did they walk after the arrest?

• Did their apparent physical limitation remain consistent throughout the encounter?

Those observations can support—or undermine—alternative explanations for field sobriety performance.

The objective should not be to manufacture a medical explanation for every clue. It should be to determine whether the officer's interpretation fairly accounts for the person's actual physical condition and the complete evidence.

Road, Weather, Lighting, and Footwear Issues During Field Sobriety Tests

Standardized field sobriety tests are called "field" tests for a reason: they are usually conducted beside a roadway rather than in a controlled environment.

That creates an unavoidable reality.

A driver may be asked to perform precise balancing and divided-attention exercises on pavement, gravel, a roadway shoulder, or another outdoor surface while dealing with darkness, weather, traffic, emergency lights, and unfamiliar footwear.

Environmental conditions do not automatically make a field sobriety test unreliable. NHTSA's field-validation research has found that varying conditions do not necessarily prevent effective testing.

At the same time, NHTSA training continues to instruct officers that, whenever possible, the Walk-and-Turn and One-Leg Stand should be conducted on a reasonably dry, hard, level, non-slippery surface under relatively safe conditions.

The actual testing environment therefore remains relevant.

The Testing Surface

The Walk-and-Turn is particularly sensitive to the testing surface because the person is expected to take precise heel-to-toe steps along a straight line.

Relevant surface conditions may include:

• Gravel;

• Loose rocks;

• Broken asphalt;

• Potholes;

• Uneven pavement;

• Roadway crowns;

• Sloped shoulders;

• Grass;

• Dirt;

• Snow;

• Ice;

• Standing water; or

• Oil, sand, or other slippery material.

A surface does not have to be perfectly flat to permit useful testing.

The important question is whether the conditions were sufficiently irregular that they could reasonably contribute to the specific behavior being interpreted as impairment.

For example, stepping several inches off a clearly visible line on clean, level pavement may be different from briefly moving a foot while attempting to walk heel-to-toe on loose gravel at the edge of a sloped highway shoulder.

A Real Line Versus an Imaginary Line

The Walk-and-Turn may be conducted using a real or imaginary straight line.

Where no actual painted line or pavement seam exists, the officer may instruct the person to imagine a line.

That does not automatically invalidate the test.

Nevertheless, video review may reveal whether the testing location provided a reasonable reference point and whether the driver understood where the officer expected them to walk.

If the officer later describes the person as "stepping off the line," it is particularly important to understand what line was actually being used.

Slope and Roadway Crown

Roadways are frequently designed with a slight slope to allow water drainage.

Shoulders may be even more substantially sloped.

A meaningful slope can affect balance, particularly during:

• The heel-to-toe instructional position;

• The Walk-and-Turn;

• The prescribed turn; and

• The One-Leg Stand.

Body-camera video sometimes makes a surface appear flatter than it actually is because of camera angle.

Dash-camera footage, photographs of the location, police diagrams, or a later inspection of the scene may occasionally provide additional context.

Rain, Snow, and Ice

Weather can affect both footing and concentration.

Rain may make painted roadway lines or pavement slick. Snow or ice may make precise heel-to-toe walking difficult even for a sober person.

If weather conditions are genuinely unsafe or unsuitable, NHTSA training materials contemplate moving the testing to a more appropriate location or relying on other investigative evidence.

The important inquiry remains practical:

What were the actual conditions, and how might they have affected the particular test?

Wind

Strong wind may potentially affect balance during the One-Leg Stand or instructional phase of the Walk-and-Turn.

A light breeze ordinarily has little significance.

Substantial wind may be more relevant, particularly when combined with poor footing, cold temperatures, or other environmental conditions.

Again, the issue is not merely whether wind existed. The issue is whether it was significant enough to provide a plausible explanation for the behavior the officer attributed to impairment.

Cold Temperatures

Cold weather can affect physical performance in several ways.

A person standing outside in winter conditions may:

• Shiver;

• Stiffen their muscles;

• Keep their hands close to their body;

• Have reduced sensation in their feet;

• Move differently because of heavy clothing; or

• Rush through instructions because of discomfort.

Shivering should not automatically be characterized as swaying or lack of coordination.

Cold weather can also affect the practicality of removing unusual footwear, which may otherwise be an option during testing.

Darkness and Lighting

Many DUI investigations occur after dark.

Adequate lighting is particularly important because the driver may be instructed to:

• Watch their feet;

• Follow a stimulus during HGN;

• Walk along a real or imaginary line; and

• Observe the officer's demonstration of the test.

Potential lighting issues include:

• Poorly illuminated roadsides;

• Headlights directed toward the person;

• Flashlights;

• Rapidly flashing emergency lights;

• Shadows; and

• Changing light conditions as vehicles pass.

Lighting should be evaluated particularly carefully in an HGN examination because the officer is making observations about eye movement.

NHTSA training also emphasizes proper stimulus positioning and visual conditions during HGN.

Emergency Lights and Other Distractions

A DUI investigation may involve patrol vehicles with flashing red, blue, or white emergency lights.

Traffic may continue passing nearby.

Other officers may be speaking. Radios may be operating. Tow trucks or emergency personnel may arrive.

These distractions do not necessarily make field sobriety testing invalid.

However, they may affect the person's ability to hear instructions, concentrate, or visually focus on what the officer is demonstrating.

Video can help determine whether distractions were minimal or substantial.

Passing Traffic and Safety Concerns

Performing balance tests immediately adjacent to moving traffic can create anxiety even for a person who is completely sober.

The driver may naturally look toward passing vehicles, move away from the traffic lane, or become distracted by headlights and noise.

NHTSA training emphasizes conducting testing from a safe position and considering subject safety.

A movement made to avoid traffic should not automatically be treated the same as an unexplained loss of balance.

Footwear

Footwear is one of the most concrete environmental factors affecting field sobriety tests.

NHTSA's current refresher materials specifically note that unusual footwear should be considered and that a subject wearing certain footwear should be afforded an opportunity to remove it.

Potentially significant footwear includes:

• High heels;

• Platform shoes;

• Flip-flops;

• Loose sandals;

• Cowboy boots;

• Heavy work boots;

• Ski or snow boots;

• Shoes with damaged soles;

• Shoes that are too large or too small; and

• Footwear with poor traction.

NHTSA's original research specifically suggested that individuals wearing heels greater than approximately two inches should be given an opportunity to remove their shoes before performing the balance tests.

The reason is intuitive: a test intended to measure balance should not unnecessarily introduce footwear that itself makes balance more difficult.

Removing Shoes Can Create Its Own Problems

The analysis does not necessarily end simply because an officer offers to let someone remove their shoes.

Barefoot testing may also raise practical concerns if the surface is:

• Extremely cold;

• Hot;

• Covered with gravel;

• Wet;

• Sharp;

• Dirty; or

• Otherwise uncomfortable or unsafe.

The relevant question is whether the person was provided a reasonable opportunity to perform the test under suitable conditions.

Clothing Can Also Affect Performance

Heavy or restrictive clothing may occasionally influence movement.

Examples could include:

• Heavy winter coats;

• Ski clothing;

• Tight skirts;

• Work equipment;

• Tool belts; or

• Other garments restricting normal leg movement.

Clothing will rarely explain an entire DUI investigation, but it may provide context for specific physical observations.

Environmental Conditions Must Be Considered Together

Often, no single environmental factor is particularly significant.

The more meaningful issue may be the combination.

Consider two very different situations:

Situation A: A person performs the Walk-and-Turn on a dry, level, well-lit parking lot while wearing ordinary athletic shoes.

Situation B: A person performs the same test at midnight on a sloped gravel shoulder, wearing heavy work boots, in freezing weather, with traffic passing several feet away.

An officer may still obtain useful observations in either situation.

But the significance of a small balance error should not necessarily be evaluated identically.

Video Is Often the Best Evidence of Testing Conditions

Police reports frequently contain a short statement such as:

"The surface was level and free of debris."

Body-camera or dash-camera footage may permit that statement to be independently evaluated.

Video may show:

• The actual pavement;

• The slope of the shoulder;

• Gravel or debris;

• Weather conditions;

• The driver's footwear;

• Traffic;

• Lighting;

• Emergency lights;

• Where the officer stood;

• Where the driver stood; and

• Whether the driver expressed concern about the conditions.

The video may confirm that the testing conditions were entirely reasonable.

Or it may reveal circumstances that deserve consideration but were not included in the report.

Either result is useful.

The purpose of reviewing environmental conditions is not to find an excuse for every mistake. It is to determine whether the field sobriety tests were administered under circumstances that allow the driver's performance to be evaluated fairly.

As with every other part of a DUI investigation, the field sobriety tests should be considered in the context of the complete evidence rather than interpreted in isolation.

How Body-Worn Camera Evidence Can Change the Analysis

Body-worn camera footage has become one of the most important sources of evidence in many DUI cases.

A police report necessarily summarizes an investigation from the officer's perspective. The report may describe driving behavior, statements, physical observations, field sobriety testing, and the reasons the officer believed an arrest was appropriate.

Video can provide something different: an opportunity to observe much of the encounter as it actually happened.

That does not mean body-camera footage always helps the defense. Sometimes the video strongly supports the officer's written observations. In other cases, however, the recording provides important context, shows a better overall performance than the report suggests, reveals problems with test administration, or documents circumstances that were not included in the written report.

For that reason, police reports and body-camera footage should generally be reviewed together rather than treating either one as a complete description of the investigation.

Comparing the Police Report With What the Video Shows

One of the first questions when reviewing a DUI video is whether the officer's written description fairly characterizes what can actually be observed.

A report may use phrases such as:

• "Unsteady on his feet";

• "Swayed significantly";

• "Had difficulty following instructions";

• "Failed to walk heel-to-toe";

• "Used arms for balance"; or

• "Appeared confused."

Those descriptions may be completely supported by the recording.

But because they are conclusions rather than measurements, video may provide important additional context.

For example, a report stating that a driver was "unsteady" may correspond on video to obvious stumbling and repeated balance problems. In another case, it may refer to a single brief movement while the person otherwise stands and walks normally.

The wording in the report may be the same. The evidentiary significance can be very different.

Seeing the Entire Performance Rather Than Only the Mistakes

Police reports understandably tend to emphasize facts the officer believes support the DUI arrest.

That can make field sobriety performance appear more one-sided than it actually was.

Suppose an officer documents that a driver:

• Missed heel-to-toe twice;

• Raised an arm once for balance; and

• Put a foot down during the One-Leg Stand.

Those observations may be relevant.

The video may also reveal, however, that the driver:

• Followed lengthy instructions correctly;

• Maintained the instructional position;

• Took the correct number of steps;

• Stayed on the line;

• Performed the prescribed turn;

• Counted correctly;

• Spoke clearly;

• Retrieved documents without difficulty; and

• Walked normally before and after the formal tests.

Correct performance does not eliminate properly observed clues. But it is part of the totality of the evidence.

A fair assessment should consider both what the person did incorrectly and what the person did correctly.

Determining Whether Instructions Were Actually Given

Body-camera footage is especially useful when the issue involves instructions.

Field sobriety tests require the driver to perform unfamiliar tasks according to specific directions. Whether a person failed to follow an instruction may therefore depend on whether the instruction was actually communicated clearly.

Video can help answer questions such as:

• Did the officer tell the person not to begin until instructed?

• Was the heel-to-toe position clearly explained?

• Did the officer demonstrate the Walk-and-Turn turn?

• Was the person told to count aloud?

• Was the person instructed to watch their feet?

• Were the One-Leg Stand instructions complete?

• Did the driver ask questions or express confusion?

• Did the officer answer those questions?

• Were instructions interrupted by another officer, traffic, radio communications, or other distractions?

This can be important because behavior should not ordinarily be characterized as failure to follow instructions that were never clearly given.

Evaluating the Officer's Demonstration

Some standardized field sobriety tests involve maneuvers that are not intuitive.

The Walk-and-Turn provides a particularly good example. The prescribed turn is not an ordinary pivot or about-face. The person is instructed to keep the front foot on the line and use the other foot to make a series of small steps around it.

Video may reveal exactly how the officer demonstrated that maneuver.

If the driver's turn differs from the officer's expectations, a reviewer can compare:

1. What the officer said;

2. What the officer demonstrated; and

3. What the driver actually did.

That comparison may provide a much more useful analysis than simply reading "improper turn" in the report.

Evaluating the Testing Surface and Environment

Body cameras may also document the conditions surrounding the testing.

The recording can sometimes show:

• Whether the surface was level or sloped;

• Whether the driver was standing on pavement, gravel, dirt, or grass;

• Rain, snow, ice, or wet pavement;

• The driver's footwear;

• Traffic passing nearby;

• Emergency lights;

• Darkness or available lighting;

• Roadside debris;

• Wind;

• Heavy clothing; and

• Other distractions.

These conditions do not automatically invalidate a test.

They may, however, provide context for a balance problem or other physical observation that the report does not fully describe.

Evaluating Medical or Physical Limitations

Video may preserve statements about medical problems that become highly relevant to later field sobriety performance.

A driver may tell the officer:

• "I have a bad knee."

• "I recently had ankle surgery."

• "I have vertigo."

• "My back is injured."

• "I cannot stand on that leg."

• "These boots make this difficult."

The important question is not simply whether the driver mentioned a condition.

The reviewer should consider:

• When was the condition disclosed?

• Did the officer ask follow-up questions?

• Was the condition visible?

• Did the officer modify or discontinue testing?

• Is the reported limitation consistent with the person's actual movements?

• Does it logically affect the particular test on which the person struggled?

Body-camera footage can preserve that exchange more accurately than a short sentence in a police report.

Observing Behavior Before the Formal Tests Begin

One of the most useful aspects of video review is that it allows the attorney to evaluate the person's behavior outside the artificial structure of the standardized tests.

For example:

• How did the driver get out of the vehicle?

• Did the driver stumble?

• How did the person walk to the testing location?

• Could the person retrieve a license, registration, or insurance card?

• Was speech understandable?

• Did the person appear oriented to what was happening?

• Could the person carry on a coherent conversation?

• Did the person follow ordinary instructions?

• How did the person walk after the arrest?

These observations can be important because a person may perform differently during an unfamiliar balance test than during ordinary movements.

Consistency across the entire encounter can strengthen or weaken competing interpretations of the evidence.

Tone and Communication May Also Matter

Written reports cannot fully reproduce tone of voice, pauses, confusion, hesitation, sarcasm, nervousness, or the dynamics of the interaction.

Video can.

A statement that appears incriminating when isolated in a report may sound different when heard in context.

Likewise, a driver whom the report characterizes as confused may appear plainly confused on video—or may appear to be asking a reasonable question about an unusual instruction.

Communication problems can also arise because of:

• Hearing impairment;

• Language differences;

• Road noise;

• Multiple officers speaking;

• Radio traffic;

• Masks or face coverings;

• Emotional distress; or

• Simple misunderstanding.

These circumstances may become relevant when an officer attributes failure to follow instructions to impairment.

HGN Presents Special Limitations on Video

Body-camera footage is generally much more useful for reviewing the Walk-and-Turn and One-Leg Stand than for independently evaluating the officer's HGN observations.

HGN involves subtle eye movements that ordinary body-camera footage often does not capture with sufficient detail.

The camera angle may be wrong, the subject's eyes may be too small in the frame, lighting may be inadequate, or the officer's body may obstruct the view.

That means an attorney usually cannot simply watch an ordinary body-camera recording and independently determine whether each HGN clue was present.

Video can still be useful, however, in evaluating how the test was administered.

It may show:

• Whether preliminary eye checks were conducted;

• Approximate stimulus positioning;

• The sequence of the examination;

• Whether the officer moved the stimulus unusually quickly;

• Whether testing was interrupted;

• Whether flashing lights or other distractions were present; and

• Whether the driver's head remained reasonably still.

The distinction is important: video may permit meaningful review of administration even when it does not permit reliable independent scoring of the eye movements themselves.

Video Can Strengthen the State's Case Too

Body-camera evidence should not be approached with the assumption that it will reveal a defense.

Sometimes it does the opposite.

Video may show:

• Pronounced balance difficulties;

• Repeated inability to understand straightforward instructions;

• Significant coordination problems;

• Admissions that are more damaging than the written report suggests;

• Obvious difficulty completing the standardized tests;

• Clear physical signs of impairment; or

• Conduct omitted from an otherwise restrained police report.

An attorney who reviews video only looking for favorable evidence risks missing the real strength of the prosecution's case.

A meaningful case evaluation requires an objective assessment of both favorable and unfavorable evidence.

Video and Chemical Test Results Should Be Considered Together

Field sobriety performance should also be evaluated alongside any breath or blood testing.

The significance of apparently good or poor roadside performance may change depending on:

• Whether chemical testing was performed;

• The reported alcohol concentration;

• The timing of the test;

• Whether drugs were suspected;

• Whether testing procedures are disputed; and

• Whether the person's behavior appears consistent or inconsistent with the reported result.

No single piece of evidence should automatically substitute for reviewing the complete case.

Why Thorough Video Review Matters

Body-camera recordings in DUI cases can be lengthy. The most important evidence is not always limited to the few minutes during which the standardized tests are administered.

Relevant information may appear:

• During the initial vehicle contact;

• While the driver searches for documents;

• During conversation before testing;

• While the driver exits the vehicle;

• Between individual tests;

• During transportation after arrest; or

• During later breath-testing procedures.

For that reason, a thorough DUI review may require watching the recording from beginning to end rather than jumping directly to the field sobriety tests.

The Video Is Evidence, Not an Answer

Body-camera footage can significantly improve the ability to evaluate a DUI investigation, but it does not necessarily provide a complete or objective answer by itself.

Cameras have limitations.

They may:

• Point in a different direction from the officer's eyes;

• Distort distance or slope;

• Fail to capture subtle eye movements;

• Have poor audio;

• Be blocked by the officer's body;

• Miss conduct occurring outside the camera's field of view; or

• Begin recording after part of the investigation has already occurred.

The proper approach is therefore not to assume that the police report is correct or that the video is superior in every respect.

Instead, the available evidence should be compared.

The police report tells what the officer says occurred. The video may show much of what occurred. Other evidence—including witness statements, chemical testing, photographs, dispatch records, and medical information—may provide additional context.

The strongest case analysis comes from considering all of those sources together rather than relying on any single piece of evidence.

How Field Sobriety Tests Are Used in an Idaho DUI Case

Field sobriety tests can play several different roles in an Idaho DUI case.

At roadside, officers generally use the tests as investigative tools to help determine whether their existing suspicion of DUI should be confirmed or dispelled. The results may then become part of the officer's decision whether probable cause exists to make an arrest.

If charges are filed, the same tests may later become evidence in motions, plea negotiations, and at trial.

Understanding those different roles is important. A field sobriety test is not itself a determination of guilt, and Idaho law does not require a driver to "fail all three tests" before an officer can make an arrest.

Instead, the legal significance of the tests depends upon the stage of the investigation and the totality of the available evidence.

Reasonable Suspicion to Conduct Field Sobriety Tests

An officer does not necessarily need probable cause to arrest someone before requesting or administering field sobriety tests.

Under Idaho appellate decisions, an officer who has reasonable suspicion that a person is driving under the influence may use field sobriety testing as part of the DUI investigation.

Reasonable suspicion is a lower standard than probable cause. It must be based on specific, articulable facts rather than a mere hunch, but it does not require the amount of evidence necessary to make an arrest.

Facts potentially contributing to reasonable suspicion may include:

• Unusual or unsafe driving;

• A traffic accident;

• Odor of an alcoholic beverage;

• Bloodshot or glassy eyes;

• Slurred speech;

• Admissions concerning drinking or drug use;

• Open alcohol containers;

• Difficulty responding to ordinary questions;

• Information provided by witnesses; and

• Other observations suggesting possible impairment.

No single factor is necessarily required.

The issue is whether the circumstances known to the officer reasonably justified extending the investigation into suspected DUI.

Field Sobriety Tests Can Confirm or Dispel Suspicion

One purpose of field sobriety testing is to give the officer additional information.

A driver may exhibit several indicators that justify investigating possible impairment but then perform well on the roadside tests. Alternatively, someone who initially displays relatively subtle signs may demonstrate significant difficulty during testing.

The tests can therefore move the investigation in either direction.

This is one reason it is misleading to think of the roadside investigation simply as a series of tests that a driver either "passes" or "fails."

The more appropriate question is what additional information the officer obtained from the testing and how that information fits with everything else the officer observed.

Field Sobriety Tests and Probable Cause to Arrest

An arrest generally requires probable cause.

In the DUI context, probable cause is evaluated based upon the totality of the circumstances known to the officer at the time of the arrest.

Field sobriety test performance may be an important component of that analysis, but it is normally considered together with other evidence.

For example, an officer may consider:

• Driving behavior;

• A collision;

• Odor of alcohol;

• Admissions about drinking;

• Speech;

• Appearance;

• Coordination;

• Open containers;

• Field sobriety test observations;

• A preliminary breath test, when applicable;

• Statements from witnesses; and

• Other circumstances surrounding the investigation.

Idaho appellate courts have repeatedly emphasized the totality of the circumstances rather than requiring any single particular fact.

That means a person can perform relatively well on some field sobriety tests and an officer may nevertheless have probable cause to make an arrest if other evidence is sufficiently strong.

The reverse is also important: poor performance on an isolated exercise should not be analyzed without considering the rest of the investigation.

Good Performance on Some Tests Does Not Necessarily Prevent an Arrest

A common misconception is that an officer cannot make a DUI arrest if the driver performs well on the Walk-and-Turn or One-Leg Stand.

That is not the law in Idaho.

In State v. Hunter, for example, the Idaho Court of Appeals considered a case in which the defendant performed well on portions of the field sobriety testing but the officer observed HGN and had additional indicators of possible alcohol impairment. The court evaluated all of the evidence together rather than treating good performance on certain physical tests as dispositive.

More recently, in State v. Cabrito, the Idaho Court of Appeals again rejected the argument that relatively good performance on some physical field sobriety tests necessarily defeated probable cause. The court considered HGN together with driving behavior, odor of alcohol, bloodshot and glassy eyes, open containers, and an admission to drinking.

The important principle is that probable cause depends upon the entire factual picture.

Good field sobriety performance can still be important defense evidence. It simply does not operate as an automatic bar to arrest.

Refusal to Perform Field Sobriety Tests May Also Be Considered

Idaho law contains an important distinction regarding refusal of field sobriety tests.

Idaho appellate courts have held that when an officer has reasonable suspicion of DUI, voluntary consent is not constitutionally required before the officer may direct a driver to perform field sobriety tests.

A driver retains the physical ability to refuse to cooperate, but Idaho courts have distinguished that ability from a constitutional right to refuse the testing.

Refusal can also have evidentiary consequences.

Idaho courts have held that refusal to participate in field sobriety tests may be considered along with the other circumstances when determining whether probable cause existed for an arrest. Courts have reasoned that, depending upon the circumstances, refusal or evasion may support an inference of consciousness of guilt.

That does not mean every refusal proves impairment.

There may be explanations for declining testing, including:

• Physical inability;

• Confusion;

• Language barriers;

• Misunderstanding the officer;

• Medical concerns; or

• Other circumstances particular to the encounter.

The surrounding facts remain important.

Field Sobriety Tests and Motions to Suppress

Field sobriety testing can become relevant to a motion to suppress, but it is important to identify exactly what constitutional issue is being challenged.

For example, potential questions may include:

• Did the officer have lawful grounds for the original traffic stop?

• If the original reason for the stop was completed, was there reasonable suspicion to extend the detention into a DUI investigation?

• Did reasonable suspicion exist when field sobriety testing began?

• Did the detention become an arrest before probable cause existed?

• Did probable cause exist when the person was actually arrested?

• Was later evidence obtained as a result of an unlawful detention or arrest?

These questions are different from simply asking whether the officer administered a field sobriety test perfectly.

An officer's failure to follow a NHTSA instruction does not automatically create a constitutional violation or require suppression of the DUI case.

Instead, a motion to suppress usually focuses on whether the officer had the legally required justification for the detention, investigation, arrest, search, or seizure at the relevant point in time.

A Poorly Administered Test Can Still Matter

Even when an administration error does not create a basis for suppression, it may still be important.

Suppose an officer reports six HGN clues but substantially deviates from the procedures the officer was trained to use.

Or suppose an officer scores Walk-and-Turn clues that are not visible on the body-camera recording.

Those issues may affect:

• The reliability of the officer's conclusions;

• The weight that should be given to the test;

• The foundation for particular testimony;

• Cross-examination of the officer;

• Plea negotiations; and

• The persuasiveness of the evidence at trial.

There is therefore an important distinction between saying:

"This test was administered incorrectly, so the entire DUI case must be dismissed,"

and saying:

"This test was administered incorrectly, which may reduce the reliability or persuasive value of the officer's conclusions."

The second statement is generally the more accurate way to analyze field sobriety test problems.

HGN Is Treated Differently From the Physical Tests

Horizontal Gaze Nystagmus occupies a somewhat different evidentiary position from the Walk-and-Turn and One-Leg Stand.

Idaho courts recognize HGN as involving scientific evidence.

In State v. Garrett, the Idaho Supreme Court recognized the scientific basis for HGN evidence but placed limits on what conclusions may properly be drawn from it.

An officer may use observed nystagmus as circumstantial evidence that a person may be under the influence of alcohol when the proper foundation exists.

HGN cannot, however, be used by itself to establish a person's specific blood alcohol concentration.

In other words, an officer should not be able to testify that a particular number of HGN clues proves that a driver's alcohol concentration was .08, .10, .15, or some other specific level.

Chemical analysis of breath or blood is used to establish alcohol concentration.

That limitation is particularly important because HGN may have causes other than alcohol consumption.

Walk-and-Turn and One-Leg Stand Are Generally Observational Evidence

The Walk-and-Turn and One-Leg Stand are treated differently from HGN.

These tests primarily generate observations about physical performance rather than a scientific measurement.

A judge or jury may hear evidence about what the officer instructed the person to do and what the officer observed.

For example, the officer might testify that the person:

• Stepped off the line;

• Left a significant gap between heel and toe;

• Used arms for balance;

• Made an incorrect turn;

• Put a foot down;

• Hopped; or

• Was unable to complete a test.

The defense may then challenge those observations through:

• Body-camera footage;

• Cross-examination;

• Evidence concerning the testing surface;

• Medical evidence;

• Evidence concerning footwear;

• Demonstration errors;

• Incomplete instructions; or

• Evidence showing substantial correct performance that was omitted from the report.

Unlike a laboratory result, the meaning of these observations often depends heavily upon context.

Field Sobriety Tests at Trial

If a DUI case proceeds to trial, field sobriety tests may become part of the State's evidence that the defendant was under the influence.

That can be particularly important when the prosecution is attempting to prove actual impairment rather than relying exclusively upon a chemical-test result.

The officer may testify about:

• Why the DUI investigation began;

• The instructions given;

• How each test was administered;

• What the officer observed;

• What clues the officer identified; and

• How those observations contributed to the officer's opinion regarding impairment.

If body-camera footage exists, relevant portions may also allow the judge or jury to see the driver's performance rather than relying entirely on the officer's description.

That can significantly change the presentation of the evidence.

Jurors can sometimes evaluate for themselves whether phrases such as "poor balance," "difficulty following instructions," or "failed to walk heel-to-toe" fairly describe what they see.

Field Sobriety Tests Do Not Establish a Specific BAC

Field sobriety tests do not measure blood alcohol concentration.

They cannot establish that someone had an alcohol concentration of .08, .10, .20, or any other particular number.

That distinction matters because Idaho DUI law permits the State to prove DUI in more than one way.

A DUI case may involve evidence that a person's alcohol concentration met or exceeded the statutory limit, evidence that the person's ability to drive was impaired, or both.

Field sobriety testing is generally directed toward observations relevant to possible impairment. Chemical testing is used when the State seeks to establish a particular alcohol concentration.

The two types of evidence should not be confused.

Strong Chemical Evidence Does Not Make Field Sobriety Evidence Irrelevant

A high breath or blood test result may become the most important evidence in a particular DUI prosecution.

Nevertheless, field sobriety testing can still matter.

For example, the roadside video and test performance may become relevant when evaluating:

• Whether probable cause existed before an evidentiary test was obtained;

• Whether the reported chemical result appears consistent with the person's observed behavior;

• Whether the officer accurately documented the investigation;

• Whether drug impairment was also suspected;

• Whether the driver had medical conditions relevant to the investigation; or

• The overall credibility of witnesses.

Conversely, strong field sobriety evidence does not eliminate the need to evaluate chemical testing independently.

Each category of evidence presents different issues.

Field Sobriety Tests Can Affect Plea Negotiations

Not every DUI case proceeds to trial.

The strength or weakness of the field sobriety evidence can therefore become important much earlier in the case.

A prosecutor reviewing a case may consider whether:

• The video strongly supports impairment;

• The defendant performed unusually well;

• Important clues are not visible on video;

• The officer departed substantially from training;

• Physical limitations provide credible alternative explanations;

• The officer's report is consistent with the recording; and

• The field sobriety evidence is consistent with the chemical testing.

A significant weakness in the roadside investigation does not guarantee a reduced charge or favorable plea agreement.

It may, however, affect the parties' evaluation of the strength of the evidence and the risks of proceeding to trial.

Likewise, video showing obvious impairment may make a favorable negotiated resolution more difficult.

Field Sobriety Tests Should Be Evaluated as Evidence, Not as a Scorecard

Perhaps the most useful way to understand field sobriety testing is to stop thinking of it as a scorecard.

The relevant questions are not simply:

How many clues did the officer write down?

or:

Did the driver pass or fail?

A more meaningful analysis asks:

• Why did the officer begin a DUI investigation?

• Were the tests properly explained?

• Were they reasonably administered?

• What did the person actually do?

• Which observations satisfy the standardized clues?

• Which observations do not?

• Were there medical or environmental explanations?

• What does the video show?

• What evidence contradicts the officer's interpretation?

• What evidence supports it?

• How does the test performance compare with the person's behavior during the rest of the encounter?

• How does it fit with the chemical-test evidence?

• What did the officer know when the arrest decision was made?

That type of analysis provides a much more accurate assessment of an Idaho DUI case than simply counting the number of alleged field sobriety test clues.

Field sobriety tests can be important evidence. But like every other part of a DUI investigation, their significance depends upon the facts of the individual case and the quality of the evidence supporting the officer's conclusions.

Related Idaho DUI Resources

Field sobriety testing is only one part of an Idaho DUI investigation. Depending on the circumstances of the case, other issues may involve breath or blood testing, driver's license consequences, prior DUI convictions, or the specific level of the DUI charge.

For additional information, see:

• Complete Guide to Idaho DUI Law — An overview of Idaho DUI law, the court process, potential penalties, and common issues that arise after an arrest.

• What Happens After a DUI Arrest in Idaho — A step-by-step explanation of what typically happens after a DUI arrest and what issues may need immediate attention.

• Idaho DUI Penalties Explained — Information about the potential criminal and driver's license consequences of an Idaho DUI conviction.

• First-Offense DUI in Idaho — Information for drivers facing their first DUI charge.

• Excessive DUI in Idaho — An explanation of Idaho's enhanced penalties when the alleged alcohol concentration is .20 or greater.

• Third-Offense/Felony DUI in Idaho — Information about felony DUI charges involving qualifying prior DUI convictions.

• Idaho Refusal Suspensions — An explanation of the separate consequences and legal issues that can arise when a driver allegedly refuses evidentiary testing.

How Long Law Office Reviews Field Sobriety Test Evidence

Field sobriety tests should not be evaluated simply by counting the number of clues listed in a police report.

When field sobriety testing is important to a DUI case, Long Law Office reviews the tests as part of the entire investigation. That may include comparing the police reports with body-worn and dash-camera footage, examining the instructions and demonstrations actually given, evaluating whether the officer followed standardized procedures, and considering medical conditions, physical limitations, footwear, the testing surface, weather, lighting, and other circumstances that may have affected performance.

The review also considers what the driver did correctly—not merely the mistakes identified by the officer—and how the field sobriety evidence fits with the driving behavior, statements, chemical testing, and other evidence in the case.

Sometimes the video strongly supports the officer's conclusions. In other cases, it may reveal that the driver's performance was better than the written report suggests, that particular observations do not appear to satisfy standardized criteria, or that additional circumstances deserve consideration.

Every case is different. The objective is to determine what the complete evidence actually shows before recommending how the case should be handled.

Discuss Your Idaho DUI Case With Long Law Office

If you have been arrested for DUI in Boise or elsewhere in southwest Idaho, the field sobriety tests are only one part of the evidence that should be reviewed before important decisions are made about your case.

Attorney Cody Long personally reviews the available evidence and works directly with clients to identify the legal and factual issues that may affect their case.

To discuss your DUI case and the options that may be available, contact Long Law Office at (208) 287-3303.