Why Field Sobriety Tests Are Unreliable — And How We Challenge Them in New Jersey DUI Cases

Key Takeaways:

1. Nearly Half of Sober People “Fail” Field Sobriety Tests. A major study found that 46% of completely sober individuals were judged “too drunk to drive” when performing field sobriety tests — highlighting the high false-positive rate.
2. The Tests Are Unfamiliar, Unnatural, and Hard to Perform. Heel-to-toe walking, balancing on one leg, or pivoting perfectly are not everyday tasks, making it extremely easy for sober drivers to appear impaired.
3. The Scoring System Is Harsh and Designed to Create Errors. Just two small mistakes on either the Walk-and-Turn or One-Leg Stand results in a “failure,” even when those mistakes have nothing to do with alcohol impairment.
4. Even Police Officers Score the Same Test Differently. NHTSA’s own research shows very poor reliability between officers. Two officers watching the same performance may reach completely different conclusions.
5. Field Sobriety Tests Don’t Measure Driving Ability. The tests measure balance, coordination, and performance under pressure — not judgment, reaction time, or the ability to safely operate a vehicle.
6. These Tests Are Highly Challengeable in Court. Because of their scientific weaknesses, strict scoring, and officer subjectivity, a skilled DUI defense attorney can undermine or exclude field sobriety test evidence at trial.

If you were pulled over for DUI in New Jersey, there’s a good chance the officer asked you to perform Standardized Field Sobriety Tests (SFSTs) — the Walk-and-Turn, the One-Leg Stand, and the Horizontal Gaze Nystagmus (HGN) test. Prosecutors often treat these tests as if they are reliable, scientific indicators of impairment.

But research shows that SFSTs are far from scientifically sound, and they often misidentify sober people as “impaired.” One of the most important studies — “Field Sobriety Tests: Are They Designed for Failure?” by researchers Spurgeon Cole and Ronald Nowaczyk — demonstrates just how unreliable these tests can be.

Spoiler alert: These tests are not accurate. At a rate of nearly 50%, sober people are deemed “too drunk” and over the legal limit.  In this blog I will break down the major problems with SFSTs, explain why these tests may not accurately reflect whether someone is impaired, and show how our firm successfully challenges them in court.

What the Research Shows: Nearly Half of Sober People “Fail”

The Clemson University study is eye-opening. Researchers videotaped 21 sober individuals, each confirmed by a breath test of 0.00%, performing standardized field sobriety tests. Certified law-enforcement officers then reviewed the footage. Here’s what they found:

• 46% of sober participants were judged “too drunk to drive.”
• Only 15% were judged impaired when performing normal tasks.
• Several sober individuals were misjudged as impaired by every officer who watched.

These findings raise a serious question: If sober people can “fail,” how reliable are these tests for determining alcohol impairment?

Why Field Sobriety Tests Often Don’t Work

1. They Require Unfamiliar, Unnatural Movements. Most people don’t spend their daily lives practicing heel-to-toe walking, one-leg balancing, or pivot turns with military precision. They certainly do not do them on the side of the road with red and blue lights flashing while under stress.
2. The Scoring System Is Harsh and Unforgiving. The Walk-and-Turn has nine clues; the One-Leg Stand has five. If you exhibit just two clues on either test, you are considered to have “failed” under National Highway Traffic Safety Administration (“NITSA”), guidelines. It is too easy to fail and the deck is stacked against you.
3. Even NHTSA’s Own Studies Show Poor Reliability. Research shows that SFSTs fall below accepted scientific standards:

• Test-retest reliability: 0.61–0.72
• Inter-rater reliability: 0.34–0.60

4. Officers Tend to “See Impairment” Because They Expect To. The video study demonstrated that officers were significantly more likely to declare a person impaired just because they watched that person perform sobriety tests. Said differently (and more bluntly), when you are pulled over on the side of the road after 2:00 a.m. and there is an odor of alcohol, regardless of whether or not you are intoxicated, the “results” in the eyes of the officer are that you are drunk.

Conclusion: SFSTs Aren’t Proof of Impairment — and They Are Absolutely Challengeable

The research article “Field Sobriety Tests: Are They Designed for Failure?” concludes that field sobriety tests may be fundamentally flawed, and officer perceptions based on these tests “may be faulty.” Despite this, New Jersey law enforcement and courts will continue to use these tests to convict individuals of DUI.  It is critical to challenge these tests at every opportunity.

How Our Firm Successfully Challenges Field Sobriety Tests

In New Jersey, the State relies heavily on SFSTs to prove DUI cases. We challenge every test, every instruction, every observation, and every assumption. Some of the challenged we present include:

1. Explore any pre-existing injuries or ailments. Everyone is different and that matters. Do you have any prior knee, back, hip, ankle, foot or balance issues? Are they treated? Even if they are not treated, it does not mean they do not exist. We collect medical records and reports showing who you are and what limitations you have. If you have been dealing with a knee injury, but don’t have it medically documented, it does not mean the condition does not exist. Medical professionals are still able to examine you and provide opinions and/or evidence (x-rays or MRIs) showing injuries that may negatively affect your ability to perform these tests.
2. We Show the Prosecutor and the Judge That These Tests Are Not Scientific. While prosecutors and judges typically rely on these tests, we are constantly showing them studies and data that show the ineffectiveness of the tests. Not only are we able to provide tons of research and data, but we also show how that information and data specifically applies to our client.
3. We Challenge Every Step of How the Officer Conducted the Test. Not only are these tests extremely unreliable, but they become even more so if they are not conducted properly. The instructions must be specifically explained, the movements performed and all of this must be done in a very specific manner. Not only does that rarely happen, but it provides our clients with plenty of defenses to SFST conclusions.
4. We Introduce the Research That Shows Sober People Fail. In addition to attacking the specific test performances, we also attack the reliability of the tests. We show the prosecutor research, like the study from this blog, that evidences the inability of these tests to be deemed reliable.
5. Challenge SFSTs Application to Drug Impairment. Not only are these SFSTs not accurate or reliable, but they have never been tested to determine drug impairment. Studies allege that if you “fail” SFSTs, you are likely over the 0.08 BAC.  There is no evidence or research to show that if you “fail” these tests that you are impaired by drugs (e.g., cocaine, marijuana or opioids).

Charged With DUI in New Jersey? We Can Help.

At Rosenberg | Perry & Associates, we handle DUI matters and SFSTs regularly. If you, or someone you care about, have been charged with a DUI, it’s important to act quickly and to understand your rights.

At Rosenberg | Perry & Associates, our team of experienced New Jersey criminal defense attorneys has helped countless clients challenge SFSTs and DUI charges. Don’t try to navigate the process alone. Contact our offices for an appointment today by calling or texting us at (609) 928-7410.