Field Sobriety Tests in Idaho: A Complete Guide

What Are Field Sobriety Tests?

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 circumstances that the officer believes may be consistent with alcohol or drug impairment.

Many people think of field sobriety tests as scientific tests that can definitively determine whether someone is under the influence. They cannot. Instead, they are investigative tools that officers use along with other evidence, such as driving behavior, statements, physical observations, and chemical testing.

The National Highway Traffic Safety Administration (NHTSA) has developed standardized procedures for three specific field sobriety tests:

  • Horizontal Gaze Nystagmus (HGN);
  • Walk-and-Turn (WAT); and
  • One-Leg Stand (OLS).

These are commonly referred to collectively as the Standardized Field Sobriety Tests, or SFSTs.

Field sobriety tests do not directly measure blood alcohol concentration and do not determine whether someone is legally guilty of DUI. Their significance depends upon how the tests were administered, what the officer actually observed, the circumstances under which testing occurred, and how the test results fit with the remainder of the evidence.

This guide explains the three standardized field sobriety tests, other roadside exercises that may be used in Idaho DUI investigations, common administration and scoring issues, physical and environmental factors that may affect performance, the importance of body-camera evidence, and how field sobriety tests may be used in an Idaho DUI case.

The Three Standardized Field Sobriety Tests

NHTSA's standardized field sobriety testing battery consists of three tests:

  • Horizontal Gaze Nystagmus;
  • Walk-and-Turn; and
  • One-Leg Stand.

“Standardized” is important. NHTSA has established procedures governing how the tests should be instructed, demonstrated, administered, observed, and scored.

The three tests examine different types of observations.

Horizontal Gaze Nystagmus (HGN) involves observations of involuntary eye movements.

Walk-and-Turn (WAT) is a divided-attention exercise requiring a person to listen to and remember instructions while performing a series of physical tasks.

One-Leg Stand (OLS) is another divided-attention exercise involving balance, coordination, counting, and following instructions.

The following sections explain how each test is generally performed and what officers are trained to observe.

Horizontal Gaze Nystagmus (HGN)

Horizontal Gaze Nystagmus is usually the first standardized field sobriety test administered during a DUI investigation.

Unlike the Walk-and-Turn and One-Leg Stand, HGN does not require the subject to walk or balance. The officer observes the person's eyes while moving a stimulus—often a pen, finger, or small light—from side to side.

What Is Nystagmus?

Nystagmus is an involuntary jerking or bouncing movement of the eyes.

Alcohol may exaggerate certain forms of horizontal gaze nystagmus. Officers are trained to look for particular eye movements that may be considered along with the other evidence in a DUI investigation.

HGN is not a direct measurement of blood alcohol concentration.

How Is the HGN Test Administered?

The officer will generally instruct the person to keep their head still and follow a stimulus using only their eyes.

Before evaluating the standardized HGN clues, the officer should conduct preliminary eye checks. The officer then moves the stimulus through a specific sequence while observing each eye.

NHTSA training addresses such details as:

  • The position of the stimulus;
  • The speed at which it should be moved;
  • How long it should be held at particular locations; and
  • The manner in which each eye should be evaluated.

Because the observations can be subtle, administration technique can become important when HGN evidence is relied upon in a DUI case.

What Are Officers Trained to Look For?

NHTSA identifies three standardized HGN clues in each eye, for a total of six possible clues:

  • Lack of smooth pursuit;
  • Distinct and sustained nystagmus at maximum deviation; and
  • Onset of nystagmus prior to approximately 45 degrees.

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

HGN and Body-Camera Video

HGN presents a special problem when reviewing body-camera footage.

The eye movements involved may be too subtle for an ordinary body camera to capture reliably. The subject may be too far from the camera, the lighting may be poor, or the officer's body may block the view.

For that reason, video often cannot establish whether a particular HGN clue was actually present.

Video may still provide useful information about how the test was administered. It may show the general testing sequence, approximate stimulus positioning, interruptions, lighting conditions, whether the subject's head remained still, and whether the officer appeared to move the stimulus unusually quickly.

The Walk-and-Turn Test

The Walk-and-Turn is a divided-attention field sobriety test.

It requires a person to listen to instructions, remember those instructions, maintain a particular stance, walk in a prescribed manner, perform an unusual turn, count, and complete the test without abandoning the instructions.

How Is the Walk-and-Turn Performed?

The officer will generally instruct the person to:

  • Place one foot directly in front of the other in a heel-to-toe position;
  • Keep their arms at their sides;
  • Remain in that position while listening to the instructions;
  • Wait until instructed to begin;
  • Take nine heel-to-toe steps along a real or imaginary straight line;
  • Count the steps aloud;
  • Watch their feet while walking;
  • Make a particular turn using a series of small steps;
  • Take nine heel-to-toe steps back; and
  • Continue until the test is completed.

The officer normally demonstrates portions of the test before the person begins.

The prescribed turn deserves particular attention because it is not the way most people would naturally turn around. The person is generally instructed to keep the front foot on the line and take several small steps around it with the other foot.

What Are Officers Trained to Look For?

NHTSA identifies eight standardized Walk-and-Turn clues:

  • Cannot maintain balance during the instructional phase;
  • Starts 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; and
  • Takes an incorrect number of steps.

These clues have particular definitions under NHTSA training.

For example, a slight space between the heel and toe does not necessarily constitute the standardized heel-to-toe clue. Likewise, merely moving slightly while standing in the instructional position is not necessarily the standardized clue for being unable to maintain balance.

Those distinctions can become important when an officer's written description is compared with video footage.

The One-Leg Stand Test

The One-Leg Stand is the third standardized field sobriety test.

Like the Walk-and-Turn, it is a divided-attention exercise. The person must maintain balance while remembering and following several instructions and counting aloud.

How Is the One-Leg Stand Performed?

The officer will generally instruct the person 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;
  • Keep both legs straight;
  • Look at the raised foot; and
  • Count aloud in the manner instructed until told to stop.

The officer generally demonstrates the test before the person begins and times the exercise for approximately 30 seconds.

What Are Officers Trained to Look For?

NHTSA identifies four standardized clues:

  • Swaying while balancing;
  • Using the arms for balance;
  • Hopping; and
  • Putting the raised foot down.

Again, the standardized definitions matter.

For example, the “uses arms for balance” clue involves moving one or both arms sufficiently away from the sides of the body. Minor ordinary hand or arm movement should not automatically be treated as the standardized clue.

If a person puts the raised foot down, NHTSA training provides instructions for having the person raise the foot again and continue the test.

Are Field Sobriety Tests Scientifically Reliable?

The three standardized field sobriety tests were developed and studied by NHTSA as investigative tools for impaired-driving investigations.

Their value depends in significant part upon standardization. The procedures used in NHTSA's research contemplated particular instructions, demonstrations, administration techniques, and scoring criteria.

That does not mean roadside conditions must be perfect or that every minor departure from an ideal procedure makes the test worthless. DUI investigations occur in the field, not in laboratories. NHTSA recognizes that conditions will not always be ideal.

At the same time, an important deviation from standardized procedures may affect the weight or reliability of an officer's conclusions.

It is also important to understand what SFSTs do not establish. They do not directly measure blood alcohol concentration, and they are not independent determinations of guilt. Performance may also be affected by medical conditions, physical limitations, testing conditions, and other circumstances unrelated to alcohol or drugs.

The proper question in an individual case is therefore not simply whether an officer recorded a certain number of clues. The tests should be evaluated according to how they were administered, what actually occurred, and how the observations fit with the remaining evidence.

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 breath or blood testing.

The HGN, Walk-and-Turn, and One-Leg Stand tests are roadside investigative tools. They are different from evidentiary chemical testing requested under Idaho's implied-consent laws.

Can You Refuse Field Sobriety Tests in Idaho?

The answer requires some care.

Idaho appellate courts have held that when an officer has reasonable suspicion to investigate DUI, field sobriety testing may be a lawful part of that investigation and voluntary consent is not constitutionally required before the officer directs the person to perform the tests.

A person can physically decline to participate, but refusal is not necessarily consequence-free. Idaho courts have held that refusal to participate in field sobriety testing may, depending upon the circumstances, be relevant evidence and may be considered in evaluating probable cause or consciousness of guilt.

This is different from refusing evidentiary testing.

Declining roadside field sobriety tests does not, by itself, trigger the driver's license suspension procedure that may result from refusing evidentiary testing under Idaho law.

For that reason, broad advice that a driver can simply “refuse everything” without possible consequences can be misleading.

Field Sobriety Tests, Roadside Breath Tests, and Evidentiary Tests Are Different

People commonly use terms such as “breathalyzer,” “breath test,” and “field sobriety test” interchangeably, but they may refer to different procedures with different legal consequences.

Field sobriety tests involve physical or eye-related observations.

A preliminary roadside breath test may be used during the investigation.

An evidentiary breath or blood test is intended to provide chemical evidence of alcohol concentration or the presence of drugs.

When reviewing a DUI case, it can be important to determine exactly which test was requested, when it was requested, what the officer told the driver, how the driver responded, and what occurred afterward.

Can an Officer Arrest Someone Who Does Not Perform Field Sobriety Tests?

Yes.

An officer does not need a completed set of field sobriety tests in every DUI investigation.

Probable cause is evaluated from the totality of the circumstances. Depending upon the case, an officer may rely upon driving behavior, an accident, odor of alcohol, admissions concerning drinking or drug use, speech, appearance, coordination, witness information, refusal to perform testing, and other observations.

The absence of completed field sobriety tests therefore does not necessarily prevent an arrest.

Non-Standardized and Optional Field Sobriety Tests

Officers sometimes use roadside exercises in addition to the three standardized tests.

These exercises should not be confused with the standardized NHTSA battery.

Idaho State Police procedure identifies several optional exercises that may be used depending upon the officer's training and the circumstances of the investigation.

Alphabet Recitation

An officer may ask a person to recite all or part of the alphabet, sometimes beginning with one letter and stopping at another.

The officer may observe whether the person understands the instructions, begins and ends at the correct points, skips or repeats letters, loses their place, or otherwise has difficulty completing the task.

Mistakes can have explanations unrelated to impairment, including language difficulties, hearing problems, anxiety, distraction, learning disabilities, or misunderstanding the instructions.

Counting Exercises

A person may be asked to count forward or backward between designated numbers.

The exercise provides the officer with observations concerning comprehension, memory, concentration, and the ability to follow a sequence of instructions.

Finger Dexterity or Finger Count

A finger-dexterity exercise generally involves touching the thumb to the fingertips in a particular sequence while counting.

The officer may observe whether the person follows the correct sequence, uses the proper fingers, counts correctly, and appears coordinated.

Hand injuries, arthritis, neurological conditions, or simple unfamiliarity with the exercise may potentially affect performance.

Modified Romberg Balance Test

The Modified Romberg Balance test is a stationary exercise.

Depending upon the officer's training, the person may be instructed to stand still, close their eyes, tilt their head back, and estimate the passage of a specified period of time.

The officer may observe balance, body sway, ability to follow instructions, and the person's estimate of time.

This type of exercise may be particularly relevant in some drug-impairment investigations.

Lack of Convergence

A Lack of Convergence evaluation involves the eyes.

The officer generally moves a stimulus toward the bridge of the person's nose while observing whether the eyes converge toward the stimulus.

Lack of convergence may be one observation considered in some drug-impairment investigations.

Finger-to-Nose

An officer with additional training may also use a Finger-to-Nose evaluation.

The person may be instructed to close their eyes, tilt their head back, extend their arms, and touch the tip of the nose using a specified finger.

The officer may observe balance, ability to follow instructions, use of the correct hand, and accuracy in touching the nose.

Why the Difference Matters

NHTSA's standardized SFST battery consists of HGN, Walk-and-Turn, and One-Leg Stand.

Other roadside exercises may provide observations that an officer considers relevant, but they should not automatically be treated as equivalent to the standardized three-test battery.

When an optional test is important to a DUI case, the analysis should consider exactly what the person was instructed to do, how the exercise was administered, what the officer observed, whether those observations are supported by video, and whether other circumstances may explain the person's performance.

Common Mistakes and Problems in Field Sobriety Testing

Field sobriety tests are intended to be administered using particular instructions, demonstrations, procedures, and scoring criteria.

An officer's departure from training does not automatically invalidate a test or require dismissal of a DUI charge. But the way the test was actually administered may affect the significance of the officer's observations.

A useful review asks two basic questions:

  1. What did the driver actually do?
  2. Was the test administered and scored consistently with the procedures the officer was trained to use?

Incomplete or Confusing Instructions

A person cannot fairly be criticized for failing to follow an instruction that was never given or was materially unclear.

The Walk-and-Turn illustrates the problem.

The person must understand the heel-to-toe stance, know not to begin until instructed, understand how many steps to take, know how to turn, understand that they must return nine steps, count aloud, watch their feet, and keep their arms at their sides.

If an officer later identifies “starts too soon” as a clue, for example, it matters whether the driver was actually told not to begin until instructed.

The same principle applies throughout field sobriety testing: performance should be compared with the instructions that were actually communicated.

Treating Behavior as a Clue When It Does Not Meet the Standardized Criteria

Another issue arises when an officer describes conduct as a standardized clue even though the behavior may not satisfy the applicable criterion.

On the Walk-and-Turn, a person's heel and toe do not necessarily have to make perfect physical contact on every step to avoid the standardized “misses heel-to-toe” clue. Under NHTSA training, the size of the gap matters.

Similarly, ordinary swaying in the heel-to-toe instructional stance is not necessarily the same as breaking the instructional position.

These distinctions may be difficult to appreciate in a written report but obvious on video.

Incorrect HGN Administration

HGN requires particular administration techniques.

Potential issues may include:

  • Holding the stimulus too close to or too far from the face;
  • Moving the stimulus too quickly;
  • Failing to hold the stimulus long enough at maximum deviation;
  • Failing to conduct the preliminary eye checks;
  • Failing to evaluate both eyes appropriately;
  • Improper stimulus positioning;
  • Significant visual distractions; or
  • Departures from the standardized testing sequence.

The significance of a particular departure depends upon what occurred and whether it reasonably affects the reliability of the officer's conclusion.

Problems With the Walk-and-Turn Demonstration

The prescribed Walk-and-Turn turn is unusual.

Because most people would not naturally perform it without instruction, an officer's explanation and demonstration can be important.

If a driver is later marked for an improper turn, a video review may ask:

  • What did the officer say?
  • What did the officer demonstrate?
  • Could the driver see the demonstration?
  • Did the driver indicate confusion?
  • Did the officer clarify the instruction?

A person can understand that they are supposed to walk nine steps, turn, and return while still misunderstanding the particular turn required by NHTSA's procedure.

Incorrect One-Leg Stand Instructions

The One-Leg Stand also has a prescribed procedure.

The person is generally instructed to raise one foot approximately six inches, keep the foot parallel to the ground, keep both legs straight, look at the raised foot, keep the arms at the sides, and count aloud until told to stop.

Potential issues may include:

  • Demonstrating the test with a bent knee;
  • Telling the person to raise the leg substantially higher than instructed;
  • Failing to tell the person to keep both legs straight;
  • Failing to tell the person to look at the raised foot;
  • Ending the test significantly early;
  • Continuing it substantially beyond the prescribed period; or
  • Treating minor ordinary movements as standardized clues.

Changing or Repeatedly Interrupting Instructions

Not every reminder during a test is improper.

An officer may appropriately remind a person of certain instructions.

The more significant issue is whether the officer materially changes the test, gives inconsistent directions, or creates confusion about what the person is expected to do.

Video can help distinguish difficulty following a clear instruction from difficulty understanding an unclear one.

Counting the Same Type of Error Multiple Times

The standardized tests use defined categories of clues.

For example, a person who misses heel-to-toe on several Walk-and-Turn steps does not thereby accumulate a new standardized heel-to-toe clue for each step.

The frequency of an error may still be relevant to the officer's overall observations, but the number of individual mistakes should not be confused with the number of standardized clues.

Focusing Only on Mistakes

Police reports naturally tend to document observations that the officer believed supported an arrest.

That can create an incomplete picture of overall performance.

A report may emphasize that a driver missed heel-to-toe, raised an arm for balance, or put a foot down.

Video may also show that the same person correctly understood the instructions, counted properly, took the correct number of steps, stayed on the line, performed the prescribed turn, spoke clearly, and otherwise displayed normal coordination.

Correct performance does not erase properly observed clues. It does provide context for evaluating how persuasive the overall performance is as evidence of impairment.

An Administration Error Does Not Automatically Defeat the Case

A minor departure from NHTSA procedures does not automatically make the entire test worthless or require dismissal of a DUI case.

Instead, the appropriate questions include:

  • What was the officer trained to do?
  • What did the officer actually do?
  • How significant was the difference?
  • Could the difference have affected the subject's performance?
  • Could it have affected the officer's interpretation?
  • What other evidence supports or contradicts the officer's conclusions?

Field sobriety testing is evidence. It is not a verdict.

Medical and Physical Conditions That Can Affect Field Sobriety Test Performance

The Walk-and-Turn and One-Leg Stand require balance, coordination, mobility, concentration, and the ability to perform unfamiliar movements.

HGN involves visual and neurological observations.

Medical and physical conditions can therefore be important when evaluating field sobriety evidence.

A medical condition does not automatically invalidate a test, and the existence of an injury does not necessarily explain every alleged clue. The question is whether a particular condition could reasonably have affected a particular observation.

Orthopedic Injuries and Mobility Problems

Knee, ankle, hip, leg, and back problems can affect the balance-based tests.

Potentially relevant circumstances include:

  • Prior knee or ankle injuries;
  • Joint replacements;
  • Arthritis;
  • Chronic back pain;
  • Recent surgery;
  • Limited range of motion;
  • Prosthetic devices; and
  • Other mobility limitations.

A person with a knee problem may have substantial difficulty standing on one leg while having no difficulty speaking normally or following instructions.

Likewise, a back problem may affect the Walk-and-Turn without explaining unrelated observations.

The analysis should therefore connect the claimed physical limitation to the particular test or clue at issue.

Inner-Ear, Balance, and Neurological Conditions

Balance depends upon the interaction of vision, the vestibular system, and information received from muscles and joints.

Vertigo, inner-ear disorders, neuropathy, prior strokes, traumatic brain injuries, tremor disorders, and other neurological conditions may potentially affect balance, coordination, gait, eye movement, or the ability to process instructions.

Again, the significance depends upon the individual and the specific observation.

Vision and Eye Conditions

Vision and neurological eye conditions may be relevant to HGN.

NHTSA training calls for preliminary checks before officers evaluate the standardized HGN clues, including observations concerning pupil size, resting nystagmus, and equal tracking.

Prior eye surgery, eye injuries, certain neurological disorders, and other conditions affecting eye movement may warrant consideration when HGN evidence is important.

Corrective lenses themselves should not be confused with evidence of impairment.

Age, Body Mechanics, and Physical Conditioning

Physical ability varies significantly from person to person.

Age, body mechanics, strength, mobility, and general physical condition may affect a person's ability to perform a heel-to-toe walk or remain on one leg for an extended period.

NHTSA training materials recognize that some people may experience greater difficulty with the balance-based tests because of physical characteristics or limitations.

The useful question in an actual case is not whether someone falls within a broad category. It is whether that particular person's physical condition reasonably affected that particular test.

Fatigue, Anxiety, and Medications

Many DUI investigations occur late at night or after a person has been awake for an extended period.

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

Anxiety can also affect roadside behavior. A driver may be standing next to moving traffic, surrounded by officers and flashing lights, concerned about arrest, and trying to remember unfamiliar instructions.

Nervousness does not automatically explain signs of impairment, but neither should every tremor, hesitation, or mistake automatically be attributed to alcohol or drugs.

Medications may also be relevant. Depending upon the medication, side effects can potentially involve balance, alertness, vision, coordination, or eye movement. Any such explanation should be evaluated based upon evidence rather than assumption.

What Did the Officer Know Before Testing?

Timing matters.

If a driver tells the officer before testing that they have had multiple knee surgeries and cannot comfortably stand on one leg, that information may be relevant when interpreting later One-Leg Stand performance.

Conversely, if the officer asks about physical limitations and the driver denies having any, that fact may also be relevant.

Body-camera footage can preserve these exchanges.

Compare the Tests With the Person's Ordinary Movements

One useful analytical technique is to compare performance during the formal tests with the person's ordinary behavior throughout the encounter.

For example:

  • How did the person exit the vehicle?
  • How did they walk to the testing location?
  • Did they stumble when they were not performing a test?
  • Could they retrieve documents?
  • Did they stand normally during conversation?
  • How did they walk after the arrest?
  • Was an alleged physical limitation consistent throughout the encounter?

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

The goal is not to invent a medical explanation for every clue. It is to determine whether the officer's interpretation fairly accounts for the person's actual physical condition.

Road, Weather, Lighting, and Footwear Issues

Field sobriety tests are usually conducted beside a roadway rather than in a controlled environment.

A person may be asked to perform precise balancing exercises on pavement, gravel, a roadway shoulder, or another outdoor surface while dealing with darkness, weather, traffic, emergency lights, and whatever footwear they happened to be wearing.

Environmental conditions do not automatically invalidate field sobriety testing. NHTSA recognizes that ideal conditions are not always available.

Nevertheless, the actual conditions may affect how particular observations should be interpreted.

Testing Surface, Slope, and the Walk-and-Turn Line

NHTSA training generally contemplates conducting the Walk-and-Turn and One-Leg Stand on a reasonably dry, hard, level, non-slippery surface when possible.

Potentially relevant conditions include:

  • Gravel or loose rocks;
  • Broken or uneven pavement;
  • Potholes;
  • Sloped shoulders;
  • Roadway crowns;
  • Grass or dirt;
  • Snow or ice;
  • Standing water; and
  • Other slippery surfaces.

A surface does not have to be perfectly flat.

The question is whether the actual condition could reasonably have contributed to the particular balance or foot-placement problem attributed to the driver.

The Walk-and-Turn may also be performed using an actual line or an imaginary line. If an officer reports that the person repeatedly stepped “off the line,” it can be important to determine what line the person was actually instructed to follow.

Weather, Lighting, and Traffic

Weather and visibility can also matter.

Rain, snow, ice, substantial wind, and very cold temperatures may affect footing, balance, concentration, or movement.

Lighting can be relevant because the person may be expected to watch their feet, observe an officer's demonstration, or visually track an HGN stimulus.

Roadside distractions can include:

  • Flashing emergency lights;
  • Passing headlights;
  • Moving traffic;
  • Police radios;
  • Other officers;
  • Tow trucks;
  • Traffic noise; and
  • Emergency personnel.

These circumstances do not automatically make testing unreliable. Their importance depends upon their actual severity and whether they provide a plausible explanation for the behavior at issue.

Footwear and Clothing

Footwear is particularly relevant to the Walk-and-Turn and One-Leg Stand.

Potentially difficult footwear can include:

  • High heels;
  • Platform shoes;
  • Flip-flops;
  • Loose sandals;
  • Heavy work boots;
  • Cowboy boots;
  • Snow boots;
  • Damaged shoes; or
  • Shoes with poor traction.

NHTSA training recognizes unusual footwear as a circumstance officers should consider and discusses giving subjects wearing certain footwear an opportunity to remove it.

Removing shoes is not necessarily an ideal solution in every case. Barefoot testing may itself be problematic when the surface is extremely cold, hot, wet, covered with gravel, or otherwise unsafe.

Heavy or restrictive clothing may occasionally affect movement as well.

Conditions Should Be Evaluated Together

Often, no single environmental circumstance is particularly significant.

The combination may matter more.

A minor balance error on a dry, level, well-lit parking lot while wearing athletic shoes may deserve different consideration from the same movement on a sloped gravel shoulder in freezing weather while the person is wearing heavy work boots and traffic is passing nearby.

Neither situation automatically determines whether the person was impaired.

The point is that context matters when interpreting physical performance.

How Body-Worn Camera Evidence Can Change the Analysis

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

A police report summarizes an investigation from the officer's perspective.

Video provides an opportunity to observe much of the interaction directly.

That does not mean body-camera evidence always helps the defense. Sometimes it strongly supports the officer's written observations. In other cases, it provides context that substantially changes how the roadside investigation appears.

Comparing the Report With the Video

A police report may describe a driver as:

  • Unsteady;
  • Swaying;
  • Confused;
  • Unable to follow instructions;
  • Failing to walk heel-to-toe; or
  • Using their arms for balance.

Those descriptions may be entirely accurate.

But video can show the degree of the behavior.

“Unsteady” might describe repeated stumbling and obvious difficulty maintaining balance. In another case, the same word may describe one brief movement during an otherwise normal encounter.

The distinction can matter.

Looking at Correct Performance as Well as Mistakes

Video also allows a reviewer to consider aspects of performance that may receive little attention in a written report.

A driver who demonstrates one or two standardized clues may nevertheless:

  • Understand lengthy instructions;
  • Count correctly;
  • Take the correct number of steps;
  • Stay on the line;
  • Make the prescribed turn;
  • Speak clearly;
  • Retrieve documents normally; and
  • Walk normally before and after the formal tests.

Those facts do not erase genuine clues.

They do help provide a complete picture of the person's performance.

Determining What Instructions and Demonstrations Were Actually Given

Body-camera footage is especially useful when instructions become an issue.

The video may show:

  • Whether the officer told the person not to begin early;
  • How the heel-to-toe stance was explained;
  • How the Walk-and-Turn turn was demonstrated;
  • Whether the person was told to count aloud;
  • Whether the One-Leg Stand instructions were complete;
  • Whether the driver expressed confusion;
  • Whether the officer clarified the instructions; and
  • Whether traffic, radio communications, or other interruptions occurred.

This can help distinguish an inability to follow a clear instruction from a misunderstanding of an unclear one.

Observing Behavior Outside the Formal Tests

Some of the most useful video evidence occurs before or after the field sobriety tests.

A reviewer may consider:

  • How the driver exited the vehicle;
  • How the person walked when not performing a test;
  • Whether documents were retrieved without difficulty;
  • The person's speech;
  • Whether conversation was coherent;
  • Whether ordinary instructions were followed;
  • The person's coordination throughout the encounter; and
  • How the person behaved after arrest.

These observations may either strengthen or weaken the inference that formal test performance reflected impairment.

Communication and Context

Video can capture tone, hesitation, nervousness, confusion, road noise, competing conversations, language difficulties, hearing issues, and other circumstances a written report cannot fully convey.

An answer that appears evasive when reduced to a sentence in a report may sound different in context.

Conversely, video may reveal impairment or confusion more clearly than the report communicates.

HGN Has Special Video Limitations

Body-camera footage is generally better suited to reviewing Walk-and-Turn and One-Leg Stand performance than independently evaluating HGN clues.

Ordinary body cameras frequently do not capture the eyes with enough clarity to determine whether nystagmus is present.

The footage may still be valuable for evaluating administration, including the testing sequence, approximate stimulus positioning, obvious timing problems, visual distractions, and interruptions.

Video Can Strengthen the Prosecution's Case

Video should not be reviewed with the assumption that it will reveal a defense.

It may show:

  • Significant balance problems;
  • Repeated inability to understand straightforward instructions;
  • Poor coordination;
  • Damaging admissions;
  • Obvious difficulty performing the tests; or
  • Signs of impairment that were understated in the written report.

An objective DUI case review should account for unfavorable evidence as carefully as favorable evidence.

Review the Entire Recording

The most important evidence may not occur during the formal SFSTs.

Relevant information can appear during:

  • Initial contact with the vehicle;
  • The driver's search for documents;
  • Conversation before testing;
  • The driver's exit from the vehicle;
  • The periods between tests;
  • Transportation after arrest; or
  • Later evidentiary testing.

For that reason, meaningful video review may require considering the entire encounter rather than watching only the few minutes devoted to field sobriety testing.

Cameras Have Limitations Too

Video is evidence, not an infallible recording of everything the officer experienced.

A body camera 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 obstructed;
  • Miss conduct outside the field of view; or
  • Begin recording after part of the encounter has occurred.

The proper approach is therefore to compare the police report, video, chemical testing, witness information, medical evidence, and other available materials rather than assuming that any single source tells the entire story.

How Field Sobriety Tests Are Used in an Idaho DUI Case

Field sobriety tests may play different roles at different stages of an Idaho DUI case.

At roadside, they may help an officer determine whether suspicion of DUI has been confirmed or dispelled and whether probable cause exists to make an arrest.

If charges are filed, the same evidence may later become relevant to motions, negotiations, and trial.

Reasonable Suspicion to Conduct Field Sobriety Tests

An officer does not need probable cause to arrest before beginning field sobriety testing.

Idaho appellate courts have held that an officer who has reasonable suspicion of DUI may use field sobriety testing as a component of the investigation.

Reasonable suspicion is a lower legal standard than probable cause. It requires specific, articulable circumstances rather than a mere hunch.

Depending upon the case, those circumstances may include unusual driving, an accident, odor of alcohol, admissions concerning drinking or drug use, physical appearance, speech, open containers, witness information, or other observations.

The legal question is whether the circumstances known to the officer reasonably justified the DUI investigation at the time the testing occurred.

Field Sobriety Tests and Probable Cause to Arrest

Probable cause is evaluated according to the totality of the circumstances known to the officer.

Field sobriety performance may be important, but it is generally only one part of the analysis.

An officer may consider:

  • Driving behavior;
  • A collision;
  • Odor of alcohol;
  • Statements concerning alcohol or drugs;
  • Speech and appearance;
  • Coordination;
  • Open containers;
  • Field sobriety test observations;
  • Preliminary testing when applicable;
  • Witness information; and
  • Other circumstances.

Idaho courts do not require a person to fail all three standardized tests before an officer can have probable cause to arrest.

Likewise, relatively good performance on the Walk-and-Turn or One-Leg Stand does not automatically defeat probable cause if other evidence is sufficiently strong.

Good performance can still be important evidence. It simply must be considered as part of the complete factual picture.

Field Sobriety Tests and Motions to Suppress

Field sobriety testing may become important in a motion to suppress, but the legal issue should be identified precisely.

Possible questions include:

  • Was the initial traffic stop lawful?
  • Was there reasonable suspicion to extend the encounter into a DUI investigation?
  • Did reasonable suspicion exist when field sobriety testing began?
  • Did a detention become an arrest before probable cause existed?
  • Did probable cause exist at the time of arrest?
  • Was later evidence obtained as a result of an unlawful detention or arrest?

These questions are different from asking whether an officer administered every SFST perfectly.

A departure from NHTSA training does not automatically create a constitutional violation or require suppression.

An administration problem can still affect the reliability or persuasive value of the officer's conclusions even when it does not independently support suppression.

HGN Is Treated Differently From the Physical Tests

Idaho courts distinguish HGN from the Walk-and-Turn and One-Leg Stand for evidentiary purposes.

Idaho courts recognize HGN as involving scientific evidence, subject to limits on what conclusions may properly be drawn from it.

HGN evidence may be used as circumstantial evidence relevant to alcohol impairment when the necessary foundation exists.

It cannot be used to establish a particular blood alcohol concentration. An officer cannot properly infer that a particular number of HGN clues proves that a person's alcohol concentration was .08, .10, .20, or some other specific number.

Walk-and-Turn and One-Leg Stand evidence is different.

Those tests principally involve observations of physical performance. An officer may testify about what the person was instructed to do and what the officer observed, while the defense may challenge those observations through video, cross-examination, evidence concerning administration, medical limitations, testing conditions, and other circumstances.

Field Sobriety Tests at Trial

If a DUI case proceeds to trial, an officer may testify about why the DUI investigation began, what instructions were given, how the tests were administered, what the officer observed, and how those observations affected the investigation.

Where video exists, the judge or jury may also be able to observe portions of the driver's actual performance.

That can be important because the fact finder may be able to evaluate whether descriptions such as “poor balance,” “failed heel-to-toe,” or “difficulty following instructions” fairly characterize what appears on the recording.

Field Sobriety Tests Do Not Establish a Specific BAC

Field sobriety tests do not measure blood alcohol concentration.

A specific alcohol concentration is ordinarily established through chemical analysis of breath or blood.

This distinction matters because an Idaho DUI prosecution may involve allegations based upon alcohol concentration, impairment, or both.

Field sobriety evidence and chemical-test evidence therefore present different issues and should be evaluated separately as well as together.

Field Sobriety Evidence Can Affect Plea Negotiations

Most criminal cases are resolved without trial.

The strength or weakness of field sobriety evidence can therefore affect how both sides evaluate a case during negotiations.

Relevant considerations may include:

  • Whether video strongly supports impairment;
  • Whether the driver performed unusually well;
  • Whether alleged clues are visible on video;
  • Whether the officer materially departed from training;
  • Whether physical limitations provide credible alternative explanations;
  • Whether the report accurately describes the recording; and
  • Whether field sobriety performance is consistent with chemical testing.

A weakness in field sobriety evidence does not guarantee a reduced charge or favorable plea agreement.

Likewise, strong field sobriety evidence does not necessarily resolve every issue in the case.

It is one component of evaluating litigation risk.

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

The most useful analysis usually goes beyond simply asking how many clues the officer recorded.

Important questions include:

  • Why did the officer begin the DUI investigation?
  • Were the tests properly explained and demonstrated?
  • What did the driver actually do?
  • Which observations satisfy standardized criteria?
  • Were there meaningful administration errors?
  • Were there medical or physical limitations?
  • Were the testing conditions significant?
  • What does the video show?
  • What did the driver do correctly?
  • How did the person behave outside the formal tests?
  • How does the SFST evidence compare with chemical testing?
  • What evidence supports the officer's interpretation?
  • What evidence contradicts it?

That approach provides a much more meaningful assessment than simply labeling the tests as “passed” or “failed.”

Related Idaho DUI Resources

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

For additional information, see:

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 evidence is important to a DUI case, Long Law Office reviews it as part of the entire investigation. That may include comparing police reports with body-worn and dash-camera footage, examining the instructions and demonstrations actually given, evaluating whether standardized procedures were followed, and considering medical limitations, testing conditions, footwear, 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 driving behavior, statements, chemical testing, and the other evidence in the case.

Sometimes the video strongly supports the officer's conclusions. In other cases, it may show that the driver's performance was better than the report suggests, that a particular observation does 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, field sobriety testing is 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 factual and legal issues that may affect the case.

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