Yes — field sobriety test results are generally admissible as evidence in a New York DWI criminal trial. But admissible doesn’t mean unbeatable. These tests are among the most frequently challenged pieces of evidence in DWI defense, and for good reason.
Here’s how they’re used against you, and where they fall apart.
What the Prosecution Uses FSTs For
When a police officer administers field sobriety tests during a traffic stop, the results serve two purposes. First, they help the officer establish probable cause to make an arrest. Second — and more importantly for trial — the results and any corresponding video footage become physical evidence of impairment that the prosecution presents to the jury.
The three tests New York police use are standardized by the National Highway Traffic Safety Administration (NHTSA): the Horizontal Gaze Nystagmus (HGN) test, the Walk-and-Turn, and the One-Leg Stand. Each test is designed to assess balance, coordination, and the ability to follow divided-attention instructions — all things that alcohol compromises. What you say and do during the stop gets recorded alongside your physical performance, and all of it feeds into the prosecution’s case.
If you performed poorly and it was captured on a dashcam or bodycam, that footage is often the most damaging piece of evidence the prosecution has — more visceral and persuasive to a jury than a BAC number on paper.
The Three Tests and How Each Gets Challenged
Horizontal Gaze Nystagmus (HGN)
This is the eye test where the officer moves an object horizontally and watches for involuntary jerking of the eye. Alcohol exaggerates this jerking, and the officer scores “clues” in each eye based on what they observe. The HGN is the most legally controversial of the three tests. Many courts require specialized expert testimony to establish its scientific validity before results can be introduced, which creates an immediate defense avenue. Conditions like certain medications, neurological disorders, and even natural nystagmus unrelated to alcohol can produce false positives.
Walk-and-Turn
The officer instructs you to walk heel-to-toe along a line, turn, and walk back. These test scores clues for things like stepping off the line, using arms for balance, taking the wrong number of steps, or starting before the instructions are finished. Challenges here focus on surface conditions (uneven pavement, gravel, grass), footwear (heels, dress shoes), lighting, and physical conditions like knee or back injuries that make the test unreliable even for sober people.
One-Leg Stand
You stand on one foot with the other raised approximately six inches off the ground and count aloud. Officers score for swaying, hopping, putting the foot down, or using arms for balance. The same environmental and physical challenges apply. Someone with an inner ear disorder, obesity, or a lower leg injury may fail this test completely regardless of their BAC.
The Core Defense Strategy: NHTSA Protocols
The three standardized FSTs only produce reliable results when administered exactly according to NHTSA protocols. These protocols specify precisely how the officer must demonstrate each test, how instructions must be given, what the testing surface must look like, and how clues must be scored. If the officer deviated from these protocols — skipped steps, gave unclear instructions, administered the test on an unsuitable surface, or scored the results inconsistently — your attorney can challenge the reliability of the results and argue they should be excluded or heavily discounted.
Officers are trained on these protocols, but training doesn’t prevent errors. Dashcam footage, bodycam footage, and cross-examination of the arresting officer often reveal protocol deviations that weren’t visible in the initial report. This is one reason why what happens during your DWI arrest matters so much to your attorney — the details of how each test was conducted are where the defense work starts.
Medical and Physical Conditions as a Defense
FSTs make assumptions about what a “normal” sober person can do. Those assumptions break down immediately when medical conditions are in play. Knee and back injuries, inner ear disorders, obesity, age, neurological conditions, and certain medications can all produce FST performance that looks like impairment but isn’t.
If you had a medical condition at the time of your stop, that information doesn’t disappear — it becomes a central element of your defense. Your attorney can introduce medical records, expert testimony, and cross-examination of the officer to demonstrate that your performance on the test reflected a physical limitation, not intoxication.
This is also why speaking to a lawyer before the chemical test — if possible — is worth prioritizing. The earlier in the process you engage counsel, the more context your attorney has about what happened and why.
How FST Results Interact with the Rest of the Case
Field sobriety tests don’t exist in isolation. They’re typically combined with officer observations (slurred speech, odor of alcohol, bloodshot eyes) and, in most cases, the results of a chemical breath or blood test. When a BAC reading is also in evidence, the FST results reinforce it. When there’s no chemical test — either because you refused or because of a timing issue — FST results carry even more weight, since the prosecution has to rely more heavily on the subjective evidence.
The accuracy questions around breathalyzers that defense attorneys routinely raise apply equally to FSTs — both can be challenged, and both challenges can succeed. A case where the FST results are suppressed or discredited, and the breathalyzer results are also challenged, leaves the prosecution with little more than an officer’s subjective observations, which is a much weaker foundation for conviction.
What About the Roadside Breath Test?
The portable breath test (PBT) administered at the roadside before arrest is different from both the FSTs and the official station test. Its results are generally not admissible as specific BAC evidence at trial — it’s used to help establish probable cause for the arrest, not to prove intoxication to a jury. This is worth understanding because many people conflate the roadside PBT with the official chemical test, when the two serve entirely different legal functions.
For the official NHTSA guidance on standardized field sobriety testing, the NHTSA SFST Practitioner’s Manual sets out the protocols that officers are required to follow — and that defense attorneys use as the benchmark when evaluating whether the tests were administered correctly.
If you’ve already taken FSTs as part of a DWI stop, an experienced DWI defense attorney can review the video, the officer’s report, and the testing conditions to identify any protocol failures or circumstances that undermine the results.
Disclaimer: This overview is for informational purposes only and does not constitute legal advice. Every case is unique — contact our legal team for personalized guidance.
