Understanding Standardized Field Sobriety Tests in Idaho: What to Expect and How an Attorney Can Help

A DUI stop in Idaho can instantly turn a routine drive into a severe legal problem. When a police officer suspects you’ve been driving under the influence, they will often ask you to perform a series of roadside exercises known as Standardized Field Sobriety Tests (SFSTs). For many people going through this for the first time, this is the most confusing and stressful part of the process.

Field Sobriety Tests are crucial because officers use them to confirm or dispel their reasonable suspicion that a driver is too impaired to drive, often leading to a DUI arrest. The officer’s claim that you “failed” these tests is powerful evidence that the prosecution uses in court. However, these tests are not foolproof. Moreover, officers oftentimes will fail to administer the tests correctly, rendering the results much less incriminating than an officer reports.

We believe that being informed about your rights and the limitations of these tests is your first line of defense. At our Boise-based law firm, we move with urgency to examine every detail of your stop and fight to challenge the reliability of the SFST evidence against you.

What Are Your Rights Regarding Standardized Field Sobriety Tests in Idaho?

A key fact to understand about roadside SFSTs is that they are not voluntary, assuming the officer has reasonable suspicion that you are in actual physical control of a motor vehicle on a public highway or private property open to the public while under the influence of drugs, alcohol, or an intoxicating substance. And although refusing to engage in SFSTs cannot result in a “refusal suspension”–that occurs when you refuse to engage in breath, blood, or urine testing–the Idaho Court of Appeals has clarified that it can serve as the basis for a conviction for obstructing an officer, a separate misdemeanor offense.

Fortunately, because SFSTs are permitted even if the officer lacks probable cause and only has reasonable suspicion of DUI, passing all three SFSTs does mean that any suspicion of DUI is dispelled as a matter of law and the DUI investigation cannot proceed any further.

Probable Cause and the Decision to Arrest

Officers use SFSTs only to gather enough probable cause to justify an arrest. Once the officer has probable cause, they place you under arrest and then invoke the Implied Consent Law. This is also the time when the refusal suspension or Administrative License Suspension comes into play with regards to the blood, breath, or urine testing.

What Are the Three Standardized Field Sobriety Tests (SFSTs) in Idaho?

In Idaho, law enforcement agencies are typically trained to administer the three tests validated by the National Highway Traffic Safety Administration (NHTSA). These are the only three tests considered “standardized” and scientifically validated for establishing probable cause.

1. Horizontal Gaze Nystagmus (HGN)

The HGN test is the most technical of the three field sobriety tests. Nystagmus is the involuntary jerking of the eyes that happens naturally when the eye moves to the side. Alcohol and certain drugs, especially depressants and antidepressants, exaggerate this jerking, cause it to occur sooner, and make it more pronounced.

• How it works: The officer will ask you to follow a small object, like a pen or their finger, with your eyes as they move it slowly from side to side
• The Clues: The officer looks for three distinct clues in each eye, totaling six clues. These include a lack of smooth pursuit, distinct and sustained nystagmus at maximum deviation, and the onset of sustained nystagmus before the eye reaches a 45-degree angle

2. Walk-and-Turn (WAT)

This test is a divided attention test, meaning it requires you to focus on both a physical task (walking) and a mental task (counting steps and following instructions) simultaneously.

• How it works: You must take nine heel-to-toe steps down a straight line, turn in a specific manner (small, prescribed steps), and then take nine heel-to-toe steps back
• The Clues: Officers look for eight possible clues of impairment. These include: not maintaining the starting position during instruction, starting too soon, not touching heel-to-toe, stepping off the line, raising arms to balance, wrong number of steps, stopping during the test, and making an improper turn

3. One-Leg Stand (OLS)

Like the WAT, the OLS is a divided attention test designed to assess your balance and ability to follow instructions under stress.

• How it works: You must stand with one foot lifted approximately six inches off the ground, with both legs straight, keeping your hands at your sides, and count out loud for 30 seconds
• The Clues: Officers look for four clues, including swaying, raising arms to balance, hopping, and putting the foot down before the count is finished

What Are the Limitations of SFSTs?

Even when administered correctly, SFSTs are validated as 100% accurate. NHTSA studies themselves indicate that the Walk-and-Turn test is about 68% accurate and the One-Leg Stand is about 65% accurate under ideal conditions. When conditions are poor or the test is improperly administered, the reliability drops even further.

Our attorneys work diligently to identify and address factors that can compromise SFST results, which can be beneficial in negotiations or in a courtroom for a jury as part of a successful DUI defense.

Improper Administration by the Officer

The primary defense against SFST evidence is proving that the officer failed to administer the tests precisely according to the standardized NHTSA protocols.

The officer must properly instruct the driver, demonstrate the steps, and score the test only using the standardized clues. If an officer deviates from the protocol, even slightly, we can argue that the test results are unreliable and should be excluded from evidence. A common error is when the officer fails to conduct the tests on a level, non-slippery surface.

Environmental and Physical Factors

The circumstances surrounding a Boise roadside stop are rarely “ideal.” We challenge the SFST results by highlighting outside factors that can skew a sober person’s performance:

• Surface: Were you standing on the uneven gravel shoulder of a highway, on a hill, or in the snow or ice often found on roads near the Boise River?
• Footwear: Did the officer fail to ask you if you prefer to remove high heels, boots, or unsupportive shoes that naturally make the tests difficult?
• Lighting and Weather: Poor lighting, heavy rain, wind, or extreme temperatures (common during Idaho winters or summers) can easily disrupt balance and concentration
• Medical Conditions: Injuries, inner ear conditions, neurological disorders, or being over 50 pounds overweight or over 65 years old are recognized factors that invalidate the standard SFSTs

These details, which an officer may overlook or ignore, can become powerful evidence when presented to a jury.

The Role of a DUI Attorney in Challenging SFST Evidence

The moment you face a DUI charge in Boise, the clock starts ticking, not just on the criminal case, but on your right to an administrative license hearing (a civil matter). We utilize our knowledge of Idaho DUI procedures to challenge the prosecution’s case from the outset.

Video Evidence Review

Most Boise officers and Ada County deputies use body cameras that record the traffic stop and the SFSTs. We urgently request this video footage. This allows us to watch the test alongside the police report and pinpoint every procedural error:

• Did the officer skip instructions?
• Was the ground uneven?
• Did the officer mistake a natural eye movement for HGN?
• Did the officer miscount your steps on the Walk-and-Turn?

Motion to Suppress

If we find significant errors in the SFST administration or constitutional violations in the traffic stop, we file a Motion to Suppress. This motion requests that the court exclude the SFST results as evidence, arguing that they are unreliable or obtained illegally. Eliminating key evidence often weakens the prosecution’s case so severely that they must dismiss or reduce the DUI charge.

Contact our Boise Law Firm to Schedule a Free Consultation with our DUI Defense Attorneys Today

Facing a DUI charge based on subjective Field Sobriety Test results requires an urgent and informative defense strategy. The team at Tatum Wysocki Law, P.C. understands the pressure you are under and the severe penalties you face under Idaho law, including mandatory jail time for repeat offenses and lengthy license suspensions.

We provide comprehensive legal assistance, reviewing every step the officer took to ensure your rights were upheld. Our goal is to challenge the evidence and help you achieve the justice you deserve.

Click to Call 208-584-2590 for a free consultation to discuss the specifics of your Boise DUI case.