Challenging “Failed” Field Sobriety Results in Bexar County
If you were recently pulled over on I-10, Loop 1604, or near the San Antonio Riverwalk, you likely underwent Standardized Field Sobriety Tests (SFSTs). Police use these tests to build a case against you, but they are far from perfect.
As a San Antonio DWI lawyer with over 20 years of experience, I know that “failing” these tests does not mean you are guilty. In Bexar County, we challenge these results by exposing officer errors, environmental factors, and medical bias.
Attorney Genaro R. Cortez | San Antonio DWI Defense | Serving Bexar County | Free Consultations | (210) 733-7575
Can You Challenge Field Sobriety Tests in San Antonio?
Many motorists believe that once an officer says they “failed,” the case is closed. This is a myth. SFST results are subjective. In San Antonio, SAPD and the Bexar County Sheriff’s Office must follow strict NHTSA (National Highway Traffic Safety Administration) guidelines. If they deviate—even slightly—from these protocols, the results may be inadmissible in court.
NHTSA’s Own “Accuracy” Numbers
According to NHTSA’s original research, when these tests are administered in a strictly standardized manner, the individual accuracy rates for identifying a BAC of 0.08% or higher are:
| Test | Reported Accuracy | Error/False Positive Rate |
| HGN (Eye Test) | 77% to 88% | ~12% to 23% |
| Walk-and-Turn | 68% to 79% | ~21% to 32% |
| One-Leg Stand | 65% to 83% | ~17% to 35% |
| Combined Battery | 82% to 91% | ~9% to 18% |
The Lawyer’s Perspective: While these percentages look high on paper, they were recorded under near-perfect conditions by specialized alcohol enforcement units. In the real world—on a sloped shoulder of I-10 with wind, traffic noise, and flashing lights—the accuracy rates drop significantly. My job is to show the jury that you fell into that ‘margin of error’ due to circumstances the officer ignored.
1. Challenging the HGN (Eye Test) in Bexar County
The Horizontal Gaze Nystagmus (HGN) test tracks involuntary eye jerking. While officers call it “scientific,” it is the test most prone to human error.
- Officer Error: Did the officer hold the stimulus (pen or light) 12–15 inches from your nose? Did they move it too fast?
- Environmental Factors: Flashing patrol car lights or passing traffic on a busy San Antonio highway can cause “optokinetic nystagmus,” which looks like intoxication but is actually a natural eye response to moving lights.
- Medical Issues: Certain neurological conditions or even high doses of aspirin can cause eye jerking that an officer might misinterpret as alcohol impairment.
Key Legal Case on Texas HGN Tests
In the landmark case of Emerson v. State, 880 S.W.2d 759, 761 (Tex. Crim. App. 1994) the Texas Court of Criminal Appeals ruled that while the HGN test is scientifically reliable, it is only admissible if the officer follows exact standardized procedures. This means that if a San Antonio officer cuts corners, skips steps, or performs the test in a way that deviates from their NHTSA training, the results can be thrown out of court. Furthermore, Emerson explicitly prohibits officers from using HGN results to estimate a specific blood alcohol concentration (BAC) percentage.
Important Emerson Case Points for San Antonio DWI Defense Cases
- HGN is “Scientific” Evidence: The court ruled that HGN is not just a “lay opinion” (like a person’s balance); it is scientific evidence. This sets a higher bar for the prosecution. They must prove the officer was specifically qualified and performed the test correctly.
- No BAC Estimates: This is a huge win for the defense. An officer can say they saw “6 clues,” but under Emerson, they are strictly forbidden from telling the jury, “Because I saw 6 clues, the defendant’s BAC was over a .10.” They can only use the test to indicate qualitative intoxication, not quantitative numbers.
- Strict Compliance Required: The court held that for the test to be considered “reliable,” the technique must have been applied properly on the occasion in question. As your lawyer, I use this ruling to scrutinize body-cam footage for any slight deviation in how the officer held the stimulus or timed the passes.
Challenge Your Bexar County DWI SFST Results – Free Consultation. Call (210) 733-7575
2. Common Mistakes in the Walk-and-Turn Test
The Walk-and-Turn is a “divided attention” test. Officers look for eight specific “clues,” but they often ignore the conditions under which you performed the test.
- Surface Conditions: Was the San Antonio roadside level? Sloped pavement, gravel, or slick surfaces during a South Texas thunderstorm can make it impossible for a sober person to maintain balance.
- Physical Limitations: If you have back, knee, or hip injuries, or if you are over 65 years old or more than 50 pounds overweight, NHTSA guidelines state this test may not be a valid indicator of impairment.
3. Why the One-Leg Stand is Often Unreliable
Standing on one leg for 30 seconds while counting out loud is a feat of balance, not just sobriety.
- The “Nervousness” Factor: Being surrounded by police lights in the middle of the night is terrifying. Anxiety causes tremors and loss of balance that have nothing to do with BAC levels.
- Roadside Distractions: High winds or the “whoosh” of passing semi-trucks can easily knock a sober driver off balance during this 30-second window.
Common Medical Conditions That Mimic Intoxication
San Antonio and Bexar County police often mistakenly attribute a driver’s poor performance on SFSTs to drinking before driving. However, the following medical conditions can make a sober driver look intoxicated:
- Inner ear disorders (affect balance on OLS and WAT)
- GERD or acid reflux (affects HGN and can skew breathalyzer)
- Diabetic hypoglycemia (mimics intoxication symptoms)
- Fatigue or sleep deprivation
- Anxiety and nervousness during the stop
- Back, knee, or hip injuries (affect WAT and OLS)
As a skilled and proven DWI lawyer, I will investigate your case to see if police mistakenly classified you as DWI based on innocent medical conditions.
The “Right to Refuse” SFSTs in Texas
A common question I hear is: “Are field sobriety tests mandatory in San Antonio?” The answer is no. In Texas, you have the right to politely refuse these roadside tests. While the officer may still arrest you based on other observations, refusing prevents the prosecution from having “video evidence” of you swaying or stumbling to show a Bexar County jury.
Why You Need an Experienced San Antonio DWI Attorney
When I review your arrest footage, I am looking for the moment the officer stopped being an investigator and started being a prosecutor. If the officer failed to account for your medical history or the uneven pavement on a San Antonio street, we will use that to fight your charges.
What happens after you fail SFSTs in Bexar County?
If you fail the SFSTs, then the police officer will arrest you and take you to the Bexar County Magistrate’s Office. They will ask you to provide a sample of your breath to test for alcohol. If you refuse, then the police officer will get a warrant to draw your blood and test it for drugs or alcohol in your system.
15-day DWI Arrest Rule
Of major interest, you have 15 days from the date of arrest to request an ALR hearing to challenge the license suspension. Otherwise, DPS will suspend your license after 40 days passes from the date of your arrest, and you will give up the right to challenge the license suspension. Your San Antonio DWI lawyer can help you with the ALR hearing.
Contact the Law Office of Genaro R. Cortez, PLLC
Don’t let a subjective “test” ruin your future. I personally handle every aspect of your defense, ensuring you aren’t just another file number in the Bexar County system. Since 2003, I have helped suspected DWI Motorists with every type of DWI defense possible.
This includes providing the following services:
- Filing Motions to Suppress the SFSTs, Breath, and Blood Draw results;
- Winning DWI cases at trial;
- Filing petitions for occupational licenses after a DWI arrest;
- Requesting reduced charges for drivers with BAC test results of higher than .15;
- Helping clients qualify for DWI deferred adjudication;
- Defending DWI first-time offenders; and
- Fight DWI MTR violations.
Call today for a free consultation: 210-733-7575
About the Author: Your San Antonio DWI Advocate Genaro R. Cortez
When you are arrested for DWI in Bexar County, the legal system can feel overwhelming and indifferent. I am a dedicated San Antonio DWI lawyer who believes that every client deserves a rigorous, detail-oriented defense.
As a solo practitioner, I personally handle every aspect of your case. From the moment we meet for your free consultation, you will work directly with me—not an assistant or a junior attorney. My goal is to protect the rights of motorists facing a DWI charge in San Antonio.
Whether this is your first-DWI offense or you are a repeat offender, I will make sure you are treated fairly and pursue the best outcome for your future.
Frequently Asked Questions About San Antonio DWI & SFSTs
Are field sobriety tests mandatory in San Antonio?
No. In Texas, you have the legal right to refuse Standardized Field Sobriety Tests (SFSTs). While an officer may not inform you of this, declining the HGN, Walk-and-Turn, or One-Leg Stand prevents the prosecution from using subjective “video evidence” against you in a Bexar County courtroom.
Can I “fail” a sobriety test if I am sober?
Yes. Statistics from NHTSA-validated studies show that even the most accurate test (the HGN) has a significant margin of error. Factors like “Cedar Fever” allergies in San Antonio, inner ear infections, or even heavy wind on a busy highway like Loop 1604 can cause a sober person to exhibit “clues” of intoxication that an officer might misinterpret.
What is the “Emerson” standard for HGN tests in Texas?
Based on the landmark case Emerson v. State, Texas courts view the HGN (eye test) as scientific evidence. This means the officer must follow exact standardized protocols for the results to be admitted. As your defense attorney, I scrutinize the arrest footage to ensure the officer didn’t move the stimulus too fast or hold it at the wrong distance, which could lead to a Motion to Suppress.
How do medical conditions affect the Walk-and-Turn and One-Leg Stand?
NHTSA guidelines explicitly state that these tests may not be valid indicators of impairment for individuals with back, leg, or knee injuries, or those who are more than 50 pounds overweight. In San Antonio, we use your medical records to prove to a jury that your “lack of balance” was a physical limitation, not alcohol impairment.
Can I fight a failed field sobriety test in San Antonio?
Yes. Police must administer the test in a specific manner. If they deviate from the rules or take short cuts during the test, then your DWI attorney can file a motion to Suppress the SFST results.
What are the three standardized field sobriety tests in Texas?
Texas law enforcement uses the three NHTSA-approved SFSTs: (1) Horizontal Gaze Nystagmus (HGN), where an officer checks for involuntary eye jerking; (2) Walk-and-Turn (WAT), a divided attention test with 8 scored clues; and (3) One-Leg Stand (OLS), where you balance on one foot for 30 seconds. Each test has strict administration requirements — deviations can invalidate the results.
How long do I have to request an ALR hearing after a DWI arrest in San Antonio?
You have only 15 days from the date of your DWI arrest to request an Administrative License Revocation (ALR) hearing with the Texas Department of Public Safety. Missing this deadline means your license will be automatically suspended and you permanently waive your right to challenge it. Call a DWI lawyer immediately after your arrest.
Can San Antonio police force a blood draw if I refuse a breath test?
Yes. If you refuse a breath test after a DWI arrest in Bexar County, SAPD or BCSO will typically obtain a warrant and require a blood draw. Blood draws are now standard procedure in Bexar County. However, an experienced DWI attorney can still challenge the results by attacking the chain of custody, lab procedures, and the validity of the warrant itself.