Legally Reviewed by Shazam Kianpour on August 20, 2026
Standardized field sobriety tests carry a documented error rate, and officers are trained to use them as one piece of evidence, not a definitive measure of impairment. Understanding how these tests actually work, where their accuracy limits come from, and how a skilled defense attorney can challenge them is essential if you are facing a DUI charge in Denver based partly or entirely on field test results.
At Shazam Kianpour & Associates, we review the administration of these tests in nearly every DUI case we handle, because how a test was conducted often matters as much as the result itself.
What Are Standardized Field Sobriety Tests?
Officers typically administer three tests that make up the National Highway Traffic Safety Administration’s Standardized Field Sobriety Test battery: the horizontal gaze nystagmus test, the walk-and-turn test, and the one-leg stand test. These three tests were selected and studied together because, according to NHTSA’s own validation research, using all three in combination produced more reliable results than any single test alone.
How Accurate Are These Tests, According to the Research Itself?
Even NHTSA’s own studies, which are the research law enforcement relies on to justify using these tests, describe accuracy rates well short of certainty. Individually, the error rate for each test in the battery has been documented at roughly 23% to 35%, depending on the specific test and study conditions. Used together, NHTSA’s research found the combined error rate could drop to around 18%, which is the basis officers rely on to establish probable cause for an arrest.
An 18% error rate, even under ideal, standardized conditions, means these tests are not a scientific measurement of blood alcohol content. They are a trained officer’s structured observation of physical coordination and eye movement, scored against a checklist. Anyone charged with DUI based substantially on field sobriety test results should understand that this checklist-based scoring is inherently more subjective than a breath or blood test.
What Can Make Field Sobriety Tests Less Reliable in Practice
The accuracy figures above assume the tests were administered under the exact standardized conditions NHTSA studied. In the field, several factors can push the real error rate even higher:
- Improper administration: Officers who deviate from the standardized instructions, skip required verbal cues, or score clues inconsistently can produce results that do not match the validated research.
- Physical conditions unrelated to alcohol: Inner ear disorders, certain neurological conditions, previous leg or back injuries, and even fatigue can produce clues on the walk-and-turn or one-leg stand tests that have nothing to do with impairment.
- Environmental factors: Uneven pavement, poor lighting, heavy traffic noise, and inappropriate footwear can all affect balance-based test performance regardless of sobriety.
- Officer bias: An officer who has already formed an opinion before the test begins may score ambiguous clues in a way that supports that opinion.
A thorough defense review looks at body camera footage, the officer’s training records, and the specific conditions at the scene to determine whether the test was administered the way NHTSA’s research actually requires.
Can Field Sobriety Test Results Be Challenged in Court?
Yes. Because these tests depend on subjective scoring and standardized administration, there are several angles a defense attorney can pursue, including whether the officer was properly trained and certified, whether the instructions were given correctly, whether the scoring matched what was actually observed on video, and whether any of the physical or environmental factors above could explain the officer’s observations without impairment. In many cases, inconsistencies between the officer’s written report and body camera footage become a central issue at trial.
Field Sobriety Tests Are Not the Whole Case
Prosecutors often build a DUI case around a combination of driving pattern, field sobriety test performance, and a breath or blood test result. Even when a breath or blood test is also part of the evidence, the field sobriety test portion of the case can still be challenged on its own terms, and a weakness there can affect how the rest of the evidence is viewed by a judge or jury.
Talk to a Denver DUI Defense Attorney
If you were arrested for DUI after performing field sobriety tests, the details of how those tests were conducted matter. Our attorneys have reviewed thousands of DUI cases across the Denver area and know what to look for in the video, the paperwork, and the officer’s training history.
Frequently Asked Questions About Field Sobriety Test Accuracy
Can I refuse a field sobriety test in Colorado?
Yes, roadside field sobriety tests are voluntary in Colorado, unlike the post-arrest chemical test required under the state’s expressed consent law. Declining a field sobriety test does not carry the same automatic license consequences as refusing a breath or blood test after a lawful arrest.
Which field sobriety test is considered the most reliable?
NHTSA’s research has generally found the horizontal gaze nystagmus test to be the most accurate of the three standardized tests when properly administered, though all three still carry a documented margin of error and are intended to be used together rather than individually.
Can a medical condition cause me to fail a field sobriety test while sober?
Yes. Conditions affecting balance, the inner ear, or the legs and back, along with certain neurological conditions, can produce clues that resemble impairment on balance-based tests even when no alcohol or drugs are involved. Documenting a relevant medical condition can be an important part of a defense.
Does failing a field sobriety test mean I will be convicted of DUI?
No. Field sobriety test results are one piece of evidence among several, and their documented error rate gives a defense attorney a genuine basis to challenge them. Whether a case results in a conviction depends on the full body of evidence and how it holds up under scrutiny.
Is body camera footage important in challenging a field sobriety test?
Body camera footage is often one of the most useful tools for comparing what actually happened during a test against the officer’s written report and scoring, and it can reveal whether the standardized instructions and scoring criteria were followed correctly.
About the Attorney
Denver Criminal Defense Attorney
Shazam Kianpour has represented clients in more than 10,000 criminal and traffic cases across the Denver area. He is a graduate of California Western School of Law, has been licensed in Colorado since 2004, and holds a Lead Counsel Verification in criminal law covering state felony, misdemeanor, and drunk driving defense.
Written by
Shazam KianpourDenver Criminal Defense Attorney & Founder, Shazam Kianpour & Associates, P.C. — Over 10,000 criminal and traffic cases handled across Colorado.