Posted on Sunday, February 1st, 2026 at 12:00 pm
When a police officer pulls you over on suspicion of driving under the influence in Illinois, one of the first things that happens is a request to perform field sobriety tests. These roadside exercises—the horizontal gaze nystagmus test, the walk-and-turn test, and the one-leg stand test—are designed to measure impairment. However, field sobriety tests are far from foolproof. In fact, they can be challenged in court, and understanding how these tests work and what your rights are can make a significant difference in your DUI case. This guide explains what field sobriety tests are, how they’re administered in Illinois, and the legal strategies Bruno Law Offices uses to challenge them on your behalf.
Why Choose Bruno Law Offices for Your Illinois DUI Defense
When you face a DUI charge in Illinois, the stakes are high. A conviction can affect your driving privileges, employment, insurance rates, and reputation. Bruno Law Offices understands the science behind field sobriety tests and the weaknesses in how they’re often administered by law enforcement. Our team has extensive experience challenging FST evidence in Illinois courts. We examine police training records, review body camera footage, and work with experts to expose errors in test administration and interpretation. We know that field sobriety tests are subjective, and we use that knowledge to build a strong defense for our clients. When you call (217) 328-6000, you’re speaking with attorneys who take your case seriously and fight aggressively to protect your rights.
What Are Field Sobriety Tests in Illinois?
Field sobriety tests are physical exercises that police officers use during DUI investigations to determine whether a driver is impaired by alcohol or drugs. Officers administer these tests at the roadside, typically after they’ve initiated a traffic stop and suspect impairment based on observations like swerving, slurred speech, or the smell of alcohol.
The primary purpose of field sobriety tests is to establish probable cause for arrest. If you perform poorly on these tests, the officer may use that as justification to arrest you and request a chemical test (breath or blood test). However, it’s important to understand that in Illinois, field sobriety tests are generally voluntary. You have the right to decline them without automatic legal penalties, though an officer may still proceed with an arrest based on other observations. Learn more about your rights during a DUI stop by contacting our Champaign DUI defense lawyers.
The Three Standardized Field Sobriety Tests
Law enforcement agencies across the United States, including Illinois, use three standardized field sobriety tests developed by the National Highway Traffic Safety Administration (NHTSA). These tests are designed to measure balance, coordination, and the ability to follow instructions—all of which can be affected by impairment. However, these same abilities can also be affected by medical conditions, environmental factors, and stress. Understanding these tests is crucial for anyone facing DUI charges in Illinois.
Horizontal Gaze Nystagmus (HGN) Test
The HGN test measures involuntary eye movements called nystagmus. During this test, an officer holds a pen or flashlight approximately 12 to 15 inches from your face and slightly higher than eye level, then moves it slowly from side to side. You’re instructed to follow the object with your eyes only, without moving your head. The officer looks for jerking movements in your eyes, particularly when your eyes are at maximum deviation (looking as far to the side as possible).
According to NHTSA standards, the officer should look for three clues in each eye: lack of smooth pursuit, distinct nystagmus at maximum deviation, and nystagmus prior to 45 degrees. If the officer observes four or more clues total, they may conclude you’re impaired.
However, the HGN test has significant weaknesses. Medical conditions like inner ear problems, certain medications, and even caffeine can cause nystagmus. Additionally, improper administration—such as moving the object too quickly, holding it too far away, or failing to keep it at the correct distance—can produce false results. Poor lighting conditions and the stress of a traffic stop can also affect your performance. Our attorneys have successfully challenged HGN test results by demonstrating administration errors and presenting medical evidence. If you’ve been charged based on an HGN test, contact our criminal defense attorneys for a free consultation.
Walk-and-Turn (WAT) Test
The walk-and-turn test requires you to walk heel-to-toe along a straight line (real or imaginary) for nine steps, turn around, and walk back nine steps. The officer provides specific instructions and demonstrates the test before asking you to perform it.
Officers look for eight specific clues during this test: inability to balance during instructions, starting before instructions are finished, stopping while walking, not touching heel-to-toe, stepping off the line, using arms for balance, an improper turn, and taking an incorrect number of steps.
The walk-and-turn test is highly subjective. What one officer considers “not touching heel-to-toe” might be a minor deviation that another officer overlooks. Environmental factors play a major role—an uneven road surface, gravel, or poor lighting can cause anyone to struggle with this test. Additionally, people with back problems, inner ear disorders, or arthritis may have difficulty maintaining balance regardless of impairment. Nervousness during a traffic stop can also affect your ability to perform well. If you’ve been charged based on poor performance on this test, Bruno Law Offices can help challenge the evidence. Our team has successfully defended clients against WAT test allegations by documenting environmental conditions and presenting expert testimony.
One-Leg Stand (OLS) Test
The one-leg stand test requires you to stand on one leg while keeping the other leg raised approximately six inches off the ground, with your arms at your sides. You must maintain this position for 30 seconds while the officer counts. The officer looks for four clues: swaying, using arms for balance, hopping, and putting your foot down.
Like the walk-and-turn test, the one-leg stand test is highly subjective and affected by numerous factors unrelated to impairment. Medical conditions affecting balance, fatigue, medications, and even the surface you’re standing on can influence your performance. Additionally, the stress and anxiety of a traffic stop can make it difficult for anyone to maintain perfect balance. Many individuals facing DUI charges based on OLS test results have successfully challenged this evidence with proper legal representation.
How Field Sobriety Tests Can Be Challenged
Field sobriety tests can be challenged in court through several strategies. First, we examine whether the officer properly administered the tests according to NHTSA standards. Many officers fail to follow proper procedures—they may not demonstrate the test correctly, provide unclear instructions, or score the clues incorrectly. This is where understanding police training and certification requirements becomes critical.
Second, we investigate the officer’s training and certification. Not all officers receive adequate training on administering and interpreting field sobriety tests. If an officer lacks proper certification or training, that weakness can be highlighted in court. We review training records and certification documents to identify gaps in the officer’s qualifications.
Third, we analyze environmental conditions at the time of the test. Poor lighting, uneven road surfaces, weather conditions, and traffic noise can all affect your ability to perform well on these tests. We document these conditions and present them as evidence that the test results are unreliable. This is particularly important in cases involving traffic stops conducted in challenging conditions.
Fourth, we examine body camera footage from the traffic stop. Video evidence often reveals administration errors, improper instructions, or environmental factors that the officer’s report doesn’t mention. This footage can be powerful evidence in your defense. For more information on how we challenge DUI evidence, see our guide on how to beat a DUI.
Finally, we work with expert witnesses who can testify about the scientific limitations of field sobriety tests and how medical conditions or environmental factors may have affected your performance. These experts can provide crucial testimony about the reliability of field sobriety tests.
Medical and Environmental Factors That Affect Test Results
Numerous medical conditions can affect your performance on field sobriety tests, even if you haven’t consumed any alcohol. Inner ear problems and vertigo cause balance issues that directly impact the walk-and-turn and one-leg stand tests. Neurological conditions, diabetes, and back pain or spinal issues can also affect coordination and balance. If you have any of these conditions, it’s essential to inform your DUI defense attorney immediately.
Medications prescribed for common conditions—including those for anxiety, depression, pain management, and allergies—can impair balance and coordination. Fatigue and the stress of a traffic stop can make it difficult to concentrate and maintain balance, even for a sober person. Many individuals don’t realize that their prescribed medications could affect their FST performance.
Environmental factors are equally important. An uneven or gravel road surface makes the walk-and-turn test significantly more difficult. Poor lighting makes it harder to see the line and maintain balance. Wind, rain, and cold temperatures affect coordination. Heavy traffic and noise can distract you and make it harder to follow instructions. All of these factors can contribute to poor performance on field sobriety tests, regardless of impairment. If you believe medical or environmental factors affected your test results, our criminal defense attorneys can evaluate your case and build a comprehensive defense strategy.
Your Rights During a DUI Stop in Illinois
Understanding your rights during a DUI stop is crucial. In Illinois, field sobriety tests are generally voluntary. You have the right to decline them without automatic legal consequences. However, refusing a field sobriety test may still factor into an officer’s decision to arrest you based on other observations. It’s important to know your constitutional rights during police interactions.
It’s important to understand the difference between field sobriety tests and chemical tests. Field sobriety tests are roadside exercises that are voluntary. Chemical tests—breath or blood tests—are different. In Illinois, if you’re arrested for DUI, you may be required to submit to a chemical test under the state’s implied consent law (625 ILCS 5/11-501.1). Understanding this distinction can significantly impact your defense strategy.
If you’re pulled over on suspicion of DUI, remain calm and polite. Don’t admit to drinking or drug use. You can politely decline field sobriety tests by saying, “I don’t wish to perform field sobriety tests.” You have the right to request an attorney before answering questions or submitting to tests. This is one of your most important communication rights for suspects.
Body camera footage from the traffic stop is critical evidence. This video can show how the officer administered the tests, what instructions were given, and what environmental conditions existed at the time. Always ask the officer if they’re recording, and remember that you can request this footage as part of your defense. For more details on your rights, see our article on what happens after a DUI refusal.
Frequently Asked Questions About Illinois DUI Field Sobriety Tests
Are field sobriety tests mandatory in Illinois?
No. Field sobriety tests are generally voluntary in Illinois. You have the right to decline them without automatic legal penalties. However, an officer may still arrest you based on other observations, such as the smell of alcohol, slurred speech, or poor performance on a preliminary breath test. Understanding your right to refuse these tests is essential.
Can field sobriety test results be used against me in court?
Yes, field sobriety test results can be used as evidence in court. However, they can also be challenged. An experienced DUI attorney can question the reliability of the tests, the officer’s training and administration, and present evidence of medical or environmental factors that affected your performance. We have successfully challenged FST evidence in numerous cases.
What if I have a medical condition that affects balance?
Medical conditions that affect balance—such as inner ear problems, neurological conditions, diabetes, or back pain—can significantly impact your performance on field sobriety tests. If you have such a condition, inform your attorney immediately. Medical records and expert testimony can help explain your performance and challenge the reliability of the test results. This is a critical component of your defense strategy.
How accurate are field sobriety tests?
Field sobriety tests are not as reliable as many people believe. While the NHTSA claims high reliability rates for these tests—77% for HGN, 68% for Walk-and-Turn, and 65% for One-Leg Stand—these figures assume perfect administration in a controlled setting. In the real world, roadside factors like flashing police lights, passing traffic, and uneven pavement significantly degrade their accuracy. This is why challenging FST evidence is so important in DUI defense.
What should I do if I’m asked to take a field sobriety test?
You have the right to decline field sobriety tests. If you choose to perform them, do your best, but remember that poor performance doesn’t necessarily mean you’re impaired. After the traffic stop, contact Bruno Law Offices immediately at (217) 328-6000. The sooner you speak with an attorney, the sooner we can begin building your defense. Time is critical in DUI cases.
Can video evidence help challenge my FST results?
Yes. Body camera footage from the traffic stop can be powerful evidence in your defense. Video can show administration errors, improper instructions, environmental conditions, and other factors that affected your performance. We request and carefully review all available video evidence in your case. This evidence often proves decisive in challenging FST allegations.
What happens if I refuse a field sobriety test?
In Illinois, Standardized Field Sobriety Tests (SFSTs) are 100% voluntary. Declining these roadside exercises does not result in an automatic license suspension. This is a critical distinction from the station-based breath or blood tests, which fall under Illinois’ implied consent law (625 ILCS 5/11-501.1) and carry mandatory penalties for refusal. However, the officer may still arrest you based on other observations. An officer may also use your refusal as evidence of consciousness of guilt, though this can be challenged in court. If you’re arrested, contact Bruno Law Offices immediately for legal representation. Understanding your right to remain silent is crucial in these situations.
Protect Your Rights With Bruno Law Offices
If you’ve been arrested for DUI in Illinois or asked to perform field sobriety tests, don’t face the charges alone. Field sobriety tests are subjective, often misapplied, and frequently influenced by factors unrelated to impairment. Bruno Law Offices has the knowledge and experience to challenge this evidence and fight for your rights.
We examine every aspect of your case—from the officer’s training and certification to the environmental conditions at the time of the stop. We review body camera footage, work with expert witnesses, and challenge the reliability of field sobriety tests in court. Our goal is to protect your driving privileges, your employment, and your future. View our case results and client testimonials to see how we’ve helped others facing DUI charges.
Our team includes experienced criminal defense attorneys who understand the complexities of DUI law in Illinois. We’ve successfully defended clients in Champaign County, McLean County, Vermilion County, and throughout central Illinois. Whether you’re facing charges in Bloomington, Danville, Decatur, or another Illinois city, we’re here to help.
Contact Bruno Law Offices today for a free consultation. Call (217) 328-6000 to speak with an attorney who understands Illinois DUI law and knows how to challenge field sobriety test evidence. The sooner you reach out, the sooner we can begin building your defense. Our Champaign criminal defense team is ready to help.