Beat an Illinois DUI: Challenge Field Sobriety Test Errors

Last reviewed: 2025-09-15

Why Field Sobriety Tests Matter in Illinois DUI Cases

Police use standardized field sobriety tests (SFSTs) to assess impairment roadside. Performance is used to justify arrest, request chemical testing, and later to persuade a judge or jury. If the tests were not properly administered, the reliability and weight of those observations can be challenged, potentially affecting probable cause and admissibility. See the Illinois DUI statute for context on DUI offenses and evidence [3], and Illinois training materials emphasizing standardized SFST procedures [2].

Illinois courts have also addressed limits on certain SFST testimony, such as the horizontal gaze nystagmus (HGN) test, which requires a proper foundation and qualified testimony before it may be admitted [4].

The Three Standardized Tests—and Where Errors Happen

Illinois officers commonly use three standardized tests: horizontal gaze nystagmus (HGN), walk-and-turn (WAT), and one-leg stand (OLS). Each has specific steps and scoring criteria. Frequent problems include:

• Unclear, incomplete, or incorrect instructions
• Failure to demonstrate the maneuver before testing
• Testing on uneven, wet, sloped, or poorly lit surfaces
• Distracting traffic or flashing lights affecting performance
• Starting the count too fast, miscounting, or double-counting “clues”
• Continuing despite reported injuries, balance disorders, or medications

These issues are inconsistent with standardized training expectations and can reduce reliability [2].

Medical and Environmental Factors That Can Skew Results

Non-alcohol causes of poor performance are common. Inner-ear or vestibular issues, back/knee/ankle injuries, neuropathy, obesity, age-related balance limits, and certain neurological conditions can impair balance and coordination. Eye conditions, contact lenses, and some prescription or over-the-counter drugs can affect eye movements relevant to HGN. Weather, footwear (heels, sandals), darkness, uneven pavement, gravel, and proximity to passing traffic can also degrade reliability. These alternative explanations can be important in court.

Challenging the Horizontal Gaze Nystagmus (HGN)

HGN has detailed administration steps (stimulus distance, smooth tracking, and specific timing). Common attack points include:

• Lack of medical screening for eye conditions or nystagmus causes unrelated to alcohol
• Incorrect stimulus distance, angle, or speed
• Improper lighting or flashing lights that can induce optokinetic nystagmus
• Missing or imprecise timing documentation

Illinois courts have recognized that HGN evidence requires a proper foundation and qualified testimony; deficiencies may lead a court to limit or exclude HGN or to give it little weight [4]. Officer training and adherence to standardized methods also matter [2].

Challenging the Walk-and-Turn (WAT) and One-Leg Stand (OLS)

These divided-attention tests are intended for reasonably dry, level, non-slippery surfaces with adequate space. Errors include failing to verify surface conditions, rushing or fragmenting instructions, not allowing removal of unstable footwear, and penalizing medically explained movements. Video can show whether the officer gave complete instructions, demonstrated properly, confirmed understanding, and followed standardized steps [2]. Deviations can reduce the reliability and weight of the results.

Officer Training, Certification, and Documentation

Standardized tests depend on standardized training. Key records include the officer’s SFST training and refresher history, certification status, and adherence to current protocols. Compare written reports to body-worn or dash camera footage for consistency. Gaps—like missing times, missing demonstrations, or shorthand scoring without detail—can support motions to limit testimony or to suppress evidence depending on the totality of the circumstances [1] [2].

Probable Cause and Suppression Motions

Even when some “clues” are present, improperly administered or unreliable tests can weaken probable cause for arrest. Illinois courts assess probable cause under the totality of the circumstances [5]. Defense strategies may include:

• Moving to suppress for lack of probable cause
• Challenging the admissibility or scope of HGN testimony if the foundation is inadequate [4]
• Seeking to exclude or limit test evidence that departs from standardized procedures [2]

Successful challenges can narrow the State’s case and influence negotiations or trial strategy. To discuss options, contact our Illinois DUI defense team.

Use Video, Medical Records, and Expert Testimony

Body and dash camera footage can reveal instruction errors, environmental problems, and a driver’s overall coordination. Medical records and treating-provider statements can document conditions affecting balance or eye movements. Expert testimony—especially from SFST instructors—can explain how deviations and outside factors reduce reliability and why fewer clues may have been appropriate.

Refusals, Alternative Explanations, and Your Statements

Your words matter. If you mentioned injuries, footwear, or surface conditions, that context should be captured in reports and video. If you declined field tests, counsel can assess whether you were properly advised and how a refusal may be used in court, consistent with Illinois law [3]. Where testing occurred, alternative explanations can reframe observed “clues” as normal responses to pain, anxiety, or environmental obstacles.

Next Steps if You Were Arrested in Illinois

• Act quickly to preserve evidence: request body/dash camera footage, dispatch logs, scene photos, and officer training/certification records.
• Gather your medical records and current medication lists.
• Avoid discussing details with anyone but your lawyer.
• Deadlines may apply to contest license consequences and to request hearings—speak with counsel promptly [3].

Get help now: request a consultation with an Illinois DUI defense attorney.

FAQ

Are field sobriety tests mandatory in Illinois?

No. They are generally voluntary, but refusal may still factor into an officer’s decision-making and the State’s arguments. Speak with counsel about how a refusal may be used in your case.

Can HGN alone establish probable cause?

Probable cause is based on the totality of the circumstances. Courts often require proper foundation and qualifications for HGN, and deficiencies can limit its weight.

What if I have a medical condition that affects balance?

Document it. Provide medical records to your attorney. Such conditions can offer legitimate alternative explanations for observed “clues.”

Will challenging SFSTs get my case dismissed?

It can lead to suppression or reduced weight of evidence, which may improve negotiation leverage or trial outcomes, but results depend on specific facts.

Talk to a lawyer now: schedule a consultation.

How Our Firm Can Help

We examine the officer’s instructions, demonstrations, scoring, and timing against standardized methods; consult with medical and SFST experts when appropriate; and file targeted motions to limit unreliable field sobriety evidence. Early involvement can expand your options. Contact us.

Sources

• Illinois State Police – Alcohol and Toxicology (SFST resources and training references)
• Illinois State Police (Training) – Standardized Field Sobriety Testing information
• Illinois Compiled Statutes – 625 ILCS 5/11-501 et seq. (Illinois DUI statute)
• People v. McKown, 226 Ill. 2d 245 (2007)
• People v. Wear, 229 Ill. 2d 545 (2008)

Disclaimer (Illinois): This post is for general information only and is not legal advice. Laws and procedures change, and outcomes depend on specific facts. Consult a licensed Illinois attorney for advice about your situation.