Illinois Field Sobriety Tests

Field Sobriety Tests (FSTs) are commonly used by law enforcement during DUI stops to evaluate whether a driver may be impaired by alcohol or drugs. The most frequently used FSTs are approved by the National Highway Traffic Safety Administration (NHTSA) as part of the Standardized Field Sobriety Test (SFST) battery. In Illinois, the three approved standardized field sobriety tests are the Horizontal Gaze Nystagmus, Walk-and-Turn, and One-Leg Stand.

When dealing with a DUI charge, it is crucial to understand how these tests are administered, their scientific foundations, and their limitations. Field sobriety test results often carry significant weight in court but are not definitive proof of impairment. In some cases, they may be challenged or excluded based on how the tests were conducted or the conditions under which they were performed.

History and Purpose

The use of standardized field sobriety tests (SFSTs) in Illinois originates from national efforts in the 1970s to improve the consistency and reliability of roadside DUI evaluations. Prior to the adoption of standardized tests, officers across jurisdictions used a wide range of informal and inconsistent physical coordination tests to assess for impairment.

In 1975, the National Highway Traffic Safety Administration (NHTSA) contracted with the Southern California Research Institute (SCRI) to study and validate field tests that could reliably indicate alcohol impairment. The resulting studies, completed in 1977, 1981, and 1983, concluded that three specific tests—Horizontal Gaze Nystagmus, Walk-and-Turn, and One-Leg Stand—were the most effective when administered under standardized procedures. These three tests formed the SFST battery that continues to be taught and used nationwide, including in Illinois.

Illinois began formally integrating the Standardized Field Sobriety Test (SFST) battery into DUI enforcement practices in the late 1980s and early 1990s, through state-funded programs administered by the Illinois Department of Transportation (IDOT) and the Illinois State Police. This timeline mirrored national efforts to standardize DUI detection procedures following the publication of NHTSA’s research on the accuracy of the SFST battery.

By the early 1990s, the Illinois Department of Transportation and the Illinois State Police incorporated SFSTs into statewide DUI enforcement training programs, including officer certification courses and continuing education initiatives. These programs were developed in accordance with NHTSA standards and were aimed at improving the consistency, reliability, and courtroom admissibility of roadside sobriety evaluations.

Since that time, Illinois law enforcement officers have been trained to administer the SFST battery—Horizontal Gaze Nystagmus, Walk-and-Turn, and One-Leg Stand—using uniform procedures outlined in state and federal training manuals. The SFSTs have become a core component of an Illinois DUI stop, with routine use to assess probable cause and to support DUI prosecutions in court.

The Three Standardized Field Sobriety Tests

Illinois police officers are trained to administer three standardized field sobriety tests: the Horizontal Gaze Nystagmus (HGN), the Walk-and-Turn (WAT), and the One-Leg Stand (OLS). These tests are designed to detect signs of physical and cognitive impairment and are considered by NHTSA to be reliable indicators of blood alcohol concentration (BAC) over 0.08 percent—if administered under ideal conditions and according to protocol.

Horizontal Gaze Nystagmus Test

The Horizontal Gaze Nystagmus (HGN) test is one of the standardized field sobriety tests used by law enforcement to assess potential alcohol impairment. It involves observing the involuntary jerking or bouncing of the eyes as they follow a moving object side to side.

During the test, the officer instructs the individual to track a stimulus—usually a pen, flashlight, or finger—with their eyes while keeping their head still. The officer looks for three specific “clues” in each eye, for a total of six possible clues:

1. Lack of Smooth Pursuit – The eye does not follow the stimulus smoothly and instead moves in a jerky fashion.
2. Distinct and Sustained Nystagmus at Maximum Deviation – The eye exhibits clear and continuous jerking when held at the farthest point to the side.
3. Onset of Nystagmus Prior to 45 Degrees – The jerking begins before the eye reaches a 45-degree angle from the center.

If an officer observes four or more of these six clues (i.e., up to three clues per eye), it is considered a strong indicator that the individual may have a blood alcohol concentration (BAC) of 0.08 or higher.

However, it’s important to note that other factors—such as certain medical conditions, prescription medications, neurological issues, and even fatigue—can also produce nystagmus. Additionally, if the test is not administered in strict accordance with standardized procedures, the results may be unreliable.

The Walk-and-Turn Test

The Walk-and-Turn test is a divided attention test that requires the subject to follow a sequence of instructions while maintaining balance and coordination. The subject is instructed to take nine heel-to-toe steps along a straight line, turn using small steps, and then take nine heel-to-toe steps back to their original place.

During the test, the officer looks for signs such as stepping off the line, failing to touch heel to toe, using arms for balance, stopping during the test, or taking the wrong number of steps. If two or more of eight standardized clues are observed, the subject is considered to show signs of impairment. Performance may be influenced by surface conditions, weather, lighting, footwear, and physical conditions unrelated to alcohol consumption, including age or injury.

The One-Leg Stand Test

The One-Leg Stand test measures divided attention and physical stability. The subject is told to raise one foot about six inches off the ground and count out loud—“one thousand one, one thousand two,” and so on—while keeping arms at their sides and eyes on the raised foot.

The officer observes the subject for thirty seconds and looks for four possible signs of impairment: swaying, hopping, using arms for balance, or putting the foot down. Two or more of these clues may indicate impairment. Factors such as uneven pavement, age, weight, medical conditions, or improper footwear may affect performance and lead to false indicators of impairment.

Are Field Sobriety Tests Required?

In Illinois, field sobriety tests are voluntary. A driver is not legally required to perform these tests during a traffic stop. However, refusal can be noted by the officer and used as circumstantial evidence in court to suggest that the driver may have been impaired. Police may also proceed with an arrest based on other observations, including driving behavior, physical appearance, and statements made during the stop.

It is important to distinguish field sobriety tests from chemical tests, such as breath, blood, or urine analysis. Under Illinois implied consent law, a driver who refuses a post-arrest chemical test faces administrative license suspension: one year for a first refusal, and three years for a second refusal within five years. These penalties apply regardless of whether the driver is ultimately convicted of DUI.

The Use of Video Recordings in DUI Cases

In many DUI investigations, field sobriety tests are recorded by dashboard cameras or body-worn cameras. These recordings can become key pieces of evidence in court. Prosecutors may present video footage to support the officer’s account of the stop and to demonstrate signs of impairment to the judge or jury. Conversely, the defense may use the same footage to challenge the officer’s interpretation of the driver’s performance, to point out inconsistencies in instructions, or to highlight conditions that may have affected the test.

Video is also commonly introduced in pretrial hearings where probable cause for arrest is being challenged. If the video does not clearly support the officer’s decision to arrest, or if it contradicts what is written in the police report, it may strengthen a motion to suppress evidence. Because these recordings provide an objective visual record, they can be especially useful in cases where the officer’s credibility is in question.

Challenging Field Sobriety Tests in Court

Field sobriety test results are not automatically accepted as proof of impairment. They are subjective assessments and can be influenced by a wide range of factors. In court, the defense may challenge the reliability and validity of the tests based on several common issues:

• The officer did not follow standardized instructions or deviated from NHTSA protocols
• The test conditions (surface, lighting, footwear) were not suitable for accurate performance
• The driver had a physical condition, injury, or disability that interfered with the test
• The officer misinterpreted or exaggerated the driver’s performance

If field sobriety test evidence is successfully challenged, it may be excluded or given less weight in the final determination of guilt. This is particularly important in cases where no chemical test results are available, or where the prosecution relies heavily on officer observations.

Free Consultations

With offices in Chicago and Naperville, Wirth Law focuses exclusively on DUI defense and Illinois driver’s license reinstatement. Our office regularly assists clients who are navigating the aftermath of a DUI. We regularly represent individuals in Cook, Will, Kane, Kendall, Lake, Kankakee, Dekalb, and Winnebago Counties, offering dedicated representation to those facing driver’s license suspension or Illinois driver’s license revocation issues. Wirth Law also represents out-of-state residents who have an Illinois hold on their driving privileges, helping clients across the country navigate the process of clearing their Illinois record so they can drive legally again.

Our practice is known for its exceptional client service and strong record of success in DUI defense and license reinstatement matters. Jennifer Wirth, managing attorney, has received multiple awards recognizing her commitment to client advocacy, including perfect “10” ratings on Avvo and Justia, the Martindale-Hubbell Client Champion Award, and selection as one of the top DUI defense attorneys in Chicago by Expertise.com. Her approach to legal representation is grounded in professionalism, compassion, and an in-depth understanding of Illinois Secretary of State hearing procedures.

At Wirth Law, every client is treated with respect and care. Our firm prioritizes clear communication, ensuring that individuals fully understand their legal options so they can make informed decisions about their case. Whether dealing with a first-time suspension or a more complex revocation after multiple DUIs, clients can expect honest guidance and skilled representation throughout the reinstatement process.

Wirth Law offers free consultations, affordable flat fees, and payment plan options through Affirm to make legal services more accessible. To schedule a consultation, contact Wirth Law at (312) 761-8290 or email jennifer@wirthlaw.org.

Further Reading: Illinois DUI Defense

• Area of Practice: Illinois DUI Defense
• Overview of a First DUI in Illinois
• Illinois Statutory Summary Suspension Law
• Aggravated DUI in Illinois
• Out-of-State DUI: Suspensions and Revocations
• Type A Injury DUI Cases
• CDL Consequences for an Illinois DUI
• Underage DUI and Zero Tolerance
• Marijuana DUI
• Prescription Drug DUI
• DUI Chemical Testing
• Illinois Field Sobriety Tests