The Flaws in Field Sobriety Tests

 Posted on June 11, 2026 in Criminal Defense

The field sobriety tests administered during Illinois DUI stops are not as reliable as law enforcement would have you believe. They are presented in court as solid proof of impairment. However, they are highly subjective, affected by many outside factors, and have real accuracy problems even under perfect conditions. If you failed a field sobriety test in 2026 and are now facing a DUI charge, that result is not the end of the story. A DuPage County DUI defense lawyer can help you challenge that evidence.

What Are the Standardized Field Sobriety Tests?

The National Highway Traffic Safety Administration, or NHTSA, recognizes three standardized field sobriety tests that officers are trained to use during DUI stops. These are the Horizontal Gaze Nystagmus test, the Walk and Turn test, and the One Leg Stand test. These are the tests most commonly used in Illinois DUI stops and the ones most likely to come up in your case.

Any other tests an officer uses, like asking you to recite the alphabet or touch your finger to your nose, are not standardized. That means they have even less scientific support than the three tests above, and their results are even easier to challenge.

How Accurate Are Field Sobriety Tests?

Even under ideal conditions, these tests get it wrong more often than most people realize. NHTSA-sponsored studies have reported accuracy rates of approximately 77 percent for the Horizontal Gaze Nystagmus test, 68 percent for the Walk and Turn test, and 65 percent for the One Leg Stand test when administered under controlled conditions.

That means even when everything goes right, these tests produce wrong results in a significant number of cases. In the real world, where conditions are rarely perfect, those numbers get worse. A completely sober person can fail a field sobriety test for reasons that have nothing to do with alcohol or drugs.

What Outside Factors Can Affect Field Sobriety Test Results?

This is one of the most important parts of challenging these results. Many things that have nothing to do with drinking can affect how someone performs on a field sobriety test.

Physical and medical factors that can affect performance include:

• Inner ear problems that affect balance

• Knee, hip, ankle, or back injuries

• Neurological conditions that affect coordination

• Vision problems

• Obesity, which makes balance tests harder

• Fatigue or illness at the time of the stop

• Age, since older people naturally have more difficulty with balance

Environmental factors can affect test results, too. Poor lighting, uneven or sloped road surfaces, wind or rain, traffic noise that makes it hard to hear instructions, and the stress of being pulled over by police can all affect results, even for someone who has not had a single drink.

How Often Do Officers Make Mistakes When Giving These Tests?

NHTSA requires officers to follow very specific steps when giving standardized field sobriety tests. The instructions have to be given a certain way, the tests have to be shown to the driver first, and the conditions have to meet certain requirements. When officers skip steps or cut corners, the reliability of the results can be called into question.

Common mistakes officers make include giving unclear or incomplete instructions and failing to demonstrate the test before asking the driver to perform it. Officers may also administer field sobriety tests on uneven ground, in poor lighting, or without considering the driver's footwear or physical limitations. Another issue is failing to properly document their observations at the time of the traffic stop.

In Illinois, if an officer did not follow NHTSA standards, your attorney can challenge the reliability and credibility of the test results.

What Can Dashcam or Body Camera Footage Show in a DUI Case?

Video from a dashcam or body camera can be one of the strongest tools in a field sobriety test challenge. The footage often tells a very different story from what an officer wrote in their report. If the video shows you performed better than the officer claimed, that conditions were poor, or that instructions were not given correctly, that can be used to seriously undermine the prosecution's case. Your attorney should request all available footage as early as possible.

Can You Refuse a Field Sobriety Test in Illinois?

In Illinois, field sobriety tests are voluntary. Unlike refusing a chemical breath or blood test, refusing field sobriety tests does not trigger Illinois' statutory summary suspension penalties. Most people do not know this, and officers are not required to tell you.

Refusing means the officer has less evidence to work with, but it does not prevent an arrest if the officer believes there is other evidence of impairment. It also does not affect your driving privileges the way refusing a chemical test can under 625 ILCS 5/11-501.2, which governs the use of chemical tests in Illinois DUI cases.

Schedule a Free Consultation With Our Wheaton, IL DUI Defense Attorney

Field sobriety tests may look like solid evidence in a DUI case, but they are far from bulletproof. Knowing how to take them apart takes experience. Our DuPage County DUI defense lawyer has practiced law in Illinois for over 30 years. His background as a law enforcement investigator, instructor, evidence technician, and police officer gives him a perspective that very few defense attorneys can offer. He knows exactly how these tests are supposed to be run, where officers cut corners, and how to use that knowledge to protect his clients. If you are facing a DUI charge in DuPage County, contact Stephen A. Brundage by calling 630-260-9647 today.