Last updated: April 24, 2026
Quick Answer: Field sobriety tests are roadside exercises police use to gather evidence of impairment before making a DUI arrest. They are not foolproof — they can be influenced by medical conditions, nerves, road conditions, and officer error. Understanding how these tests work is the first step toward building a real defense strategy.
Key Takeaways
- There are three standardized field sobriety tests approved by the National Highway Traffic Safety Administration (NHTSA): the Horizontal Gaze Nystagmus (HGN), Walk-and-Turn, and One-Leg Stand.
- Police use these tests to build probable cause for a DUI arrest — not to prove guilt.
- Results are highly subjective and depend heavily on the officer’s training and judgment.
- Many sober people fail these tests due to anxiety, physical conditions, age, or poor testing conditions.
- You have the right to know whether field sobriety tests are even reliable before deciding how to respond.
- Illinois law does not require you to perform field sobriety tests — but refusing has consequences worth understanding.
- A skilled defense attorney can challenge how these tests were administered, scored, and recorded.
- Dashcam and body camera footage can either support or undermine an officer’s claims about your performance.
What Are Field Sobriety Tests and Why Do Police Use Them?
Field sobriety tests (FSTs) are physical and cognitive exercises administered roadside when an officer suspects a driver is impaired. Police use them to create documented evidence of impairment that supports a DUI arrest and, later, a prosecution.
The key word here is documented. An officer’s observations during these tests go directly into a police report. That report becomes part of the case against you.
The NHTSA developed three standardized tests in the 1970s and 1980s. These are the only tests with published research behind them — and even that research has been questioned by defense experts. Non-standardized tests (like reciting the alphabet or touching your finger to your nose) carry even less scientific weight.
The three NHTSA-approved standardized field sobriety tests are:
| Test | What It Measures | NHTSA Accuracy Claim* |
|---|---|---|
| Horizontal Gaze Nystagmus (HGN) | Involuntary eye movement | ~77% |
| Walk-and-Turn | Balance, instruction-following | ~68% |
| One-Leg Stand | Balance, divided attention | ~65% |
*Accuracy figures are from NHTSA’s own studies conducted under controlled conditions — not real-world roadside scenarios. Independent researchers have questioned these numbers.
How Each Field Sobriety Test Works — and Where They Can Fail
Each test has a specific protocol. When an officer deviates from that protocol, the results can be challenged. This is one of the most powerful defense angles available.
Horizontal Gaze Nystagmus (HGN)
The officer moves a pen or finger slowly across your field of vision and watches for involuntary jerking of the eye (nystagmus). Alcohol can cause this jerking to appear at certain angles.
Common problems with HGN:
- Over 40 medical conditions and medications can cause nystagmus unrelated to alcohol
- Officers must follow a precise, timed protocol — many don’t
- Lighting conditions and the angle of the stimulus affect results
- This test cannot be reviewed on dashcam footage the same way physical tests can
Walk-and-Turn Test
You walk nine heel-to-toe steps along a line, turn, and walk back. The officer watches for eight specific “clues” of impairment, such as stepping off the line or using arms for balance.
Learn more about the Walk-and-Turn test and what officers are actually watching for.
Common problems:
- Uneven pavement, gravel, or slopes affect performance dramatically
- High heels, injuries, or inner ear conditions cause balance issues unrelated to impairment
- The officer must give specific instructions — if they rush or skip steps, the test is compromised
One-Leg Stand Test
You stand on one leg, count aloud, and hold the position for 30 seconds. Officers watch for swaying, hopping, putting the foot down, or using arms for balance.
See a detailed breakdown of the One-Leg Stand test and its limitations.
Common problems:
- Anyone over 65, overweight, or with leg or back problems will struggle regardless of sobriety
- Wind, passing traffic, and poor lighting all affect performance
- 30 seconds feels much longer under stress — and stress itself affects balance
Defense angle: If the officer did not follow the NHTSA protocol exactly, the test results may be inadmissible or at least seriously undermined at trial.
Should You Take Field Sobriety Tests If Pulled Over?
This is one of the most common questions people ask — and the answer is more nuanced than a simple yes or no. In Illinois, you are not legally required to perform field sobriety tests. They are voluntary.
Choose to decline if:
- You have any physical condition, injury, or disability that affects balance
- You are over 50 (balance naturally declines with age)
- Road or weather conditions are poor
- You are extremely anxious (which is almost everyone during a traffic stop)
Understand the tradeoff: Refusing does not mean you won’t be arrested. An officer can still arrest you based on other observations. However, declining means there is less performance evidence for the prosecution to use.
What you say and do during the stop matters enormously. Understanding when police read Miranda rights and what you’re obligated to say is critical knowledge before you’re ever in that situation.
How Police Use Field Sobriety Test Results to Build a DUI Case
The officer’s goal during a traffic stop is to gather enough evidence to establish probable cause for arrest. Field sobriety tests are one tool in that process — but they’re rarely the only one.
A typical DUI evidence-building sequence looks like this:
- Officer observes a traffic violation or erratic driving
- Officer approaches and notes odor of alcohol, slurred speech, or red eyes
- Officer requests field sobriety tests
- Officer documents “clues” observed during each test
- Officer requests a preliminary breath test (PBT) at the roadside
- Officer makes arrest decision based on the totality of observations
- Officer writes a detailed police report supporting the arrest
Every step in this chain can be challenged. Dashcam footage often captures the actual test performance — and sometimes it contradicts what the officer wrote in the report. Body camera footage can do the same, and police misuse of that footage is a real issue that a defense attorney will investigate immediately.
What Are the Most Effective Defense Strategies Against Field Sobriety Test Evidence?
A proven defense against field sobriety test evidence targets the test itself, the conditions, and the officer’s conduct. No single strategy fits every case — but several approaches consistently produce results.
Top defense strategies include:
- Protocol violations: Was the test administered exactly as NHTSA requires? Any deviation weakens the results.
- Environmental factors: Poor lighting, uneven surfaces, weather, and traffic noise all affect performance.
- Medical conditions: Documented conditions that affect balance, vision, or coordination can explain poor performance without impairment.
- Officer qualifications: Was the officer properly trained and certified to administer standardized FSTs?
- Footage review: Dashcam and body camera video frequently tells a different story than the police report.
- Challenging the initial stop: If the officer lacked legal justification to pull you over, all evidence gathered afterward may be suppressed.
For a deeper look at proven approaches, see best defense strategies for DUI cases.
The goal is to fight every link in the chain of evidence — aggressively and strategically. One broken link can change the outcome of the entire case.
What Happens After a DUI Arrest in Illinois?
An arrest based on field sobriety test results is just the beginning of the legal process. Illinois DUI law carries serious consequences, and the clock starts immediately.
Key things that happen after a DUI arrest:
- Your license faces automatic statutory summary suspension — this begins 46 days after the notice of suspension
- You have a narrow window to request a hearing to challenge that suspension
- Chemical test results (breath, blood, or urine) become part of the prosecution’s case
- A criminal charge is filed, and court dates begin
Understanding what happens after a DUI arrest in Chicago — and acting fast — is essential to protecting your license and your future.
A local attorney with experience in Cook County courts knows the prosecutors, the judges, and the specific procedures that affect your case. That local experience is not a small thing. It’s often the difference between a conviction and a dismissal.
FAQ: Field Sobriety Tests and DUI Defense
Q: Can I refuse a field sobriety test in Illinois? Yes. Field sobriety tests are voluntary in Illinois. Refusing does not automatically result in license suspension, unlike refusing a chemical breath test.
Q: Will refusing a field sobriety test make me look guilty? An officer may note your refusal, but a jury cannot be told to treat refusal as evidence of guilt in Illinois. An attorney can control how this is framed.
Q: Can a sober person fail a field sobriety test? Absolutely. Research and real-world cases consistently show that sober individuals fail these tests due to nerves, physical conditions, age, and poor testing conditions.
Q: Are field sobriety tests admissible in court? Generally yes, but their weight can be challenged. If the officer didn’t follow proper protocol, a judge may limit or exclude the evidence.
Q: What if the dashcam shows I performed better than the officer claimed? That footage is powerful defense evidence. An attorney should obtain and preserve it immediately — footage can be overwritten or lost if not requested quickly.
Q: Does failing a field sobriety test mean I’ll be convicted? No. It means the officer had probable cause to arrest you. The prosecution still must prove guilt beyond a reasonable doubt at trial.
Q: Can a DUI charge be dismissed in Chicago? Yes — and it happens more often than people expect when the right defense strategy is applied. Learn more about when a DUI can be dismissed in Chicago.
Q: How important is it to hire an attorney quickly after a DUI arrest? Immediate action is critical. Evidence must be preserved, deadlines for license hearings must be met, and the defense strategy must be built before the prosecution gets too far ahead.
Conclusion: Don’t Let a Roadside Test Define Your Future
Field sobriety tests are designed to build a case against you — not to find the truth. They are subjective, affected by dozens of outside factors, and frequently administered incorrectly. That’s not a loophole. That’s the law working as it should.
Here’s what to do right now if you’re facing DUI charges:
- Say nothing beyond basic identification — anything else can be used against you
- Request an attorney immediately — this is your right and your best protection
- Write down everything you remember about the stop, the tests, and the officer’s conduct
- Do not assume the evidence against you is solid — it rarely is without a fight
- Contact a defense attorney with local experience in Illinois DUI law as soon as possible
The prosecution will use every piece of evidence they have. A skilled defense attorney will challenge every piece of evidence they have. That’s the strategy. That’s the fight worth having.
If you or someone you know is facing a DUI charge in Chicago or Cook County, connect with an experienced Chicago criminal defense attorney who knows how to defend these cases aggressively — and who has the proven results to back it up.
References
- National Highway Traffic Safety Administration (NHTSA). DWI Detection and Standardized Field Sobriety Testing: Participant Manual. U.S. Department of Transportation, 2018. https://www.nhtsa.gov
- Hlastala, M.P., et al. “Accuracy of Field Sobriety Tests.” Journal of Studies on Alcohol, 2005.
- Burns, M., and Moskowitz, H. Psychophysical Tests for DWI Arrest. NHTSA Report, 1977.
- Cole, S., and Nowaczyk, R.H. “Field Sobriety Tests: Are They Designed for Failure?” Perceptual and Motor Skills, 1994.
- Illinois Compiled Statutes, 625 ILCS 5/11-501 (DUI statute) and 625 ILCS 5/11-501.1 (implied consent).
