Field Sobriety Test Lawyer Austin: What the Tests Actually Prove

A field sobriety test lawyer Austin drivers call after a stop on Lamar or Riverside usually starts with the video. The three roadside tests an Austin police officer gives are not a general check for clumsiness. They are a standardized battery designed by the National Highway Traffic Safety Administration, with a fixed set of clues and a fixed scoring threshold for each test. The officer must give them the same way every time. When that happens, the tests are evidence of impairment. Otherwise, the tests become evidence about the officer. Understanding what each test actually measures explains why so much of a Travis County DWI case turns on twelve minutes of roadside footage.

The Three Tests and Their Clues

The standardized battery has three parts. First, horizontal gaze nystagmus checks for an involuntary jerking of the eyes as they track a stimulus. The officer looks for three clues in each eye: lack of smooth pursuit, distinct and sustained nystagmus at maximum deviation, and onset of nystagmus before 45 degrees. That makes six possible clues. Second, the walk-and-turn has eight: losing balance during instructions, starting too soon, stopping while walking, missing heel to toe, stepping off the line, using arms to balance, turning improperly, and taking the wrong number of steps. Third, the one-leg stand has four: swaying, using arms, hopping, and putting the foot down. Under the NHTSA protocol, two clues on the walk-and-turn or one-leg stand mark the decision point, as do four clues on the eye test.

What a Field Sobriety Test Lawyer Austin Drivers Hire Looks For

The clues only mean something if the officer administered the test correctly. Each test has scripted instructions, a demonstration, and conditions the officer must control. The walk-and-turn needs a real or imaginary straight line and a reasonably level surface. The one-leg stand runs for 30 seconds. Likewise, the eye test requires the officer to hold the stimulus at a set distance and move it at a set pace. Austin’s body-camera footage often shows a test given on a sloped shoulder, in the wind, or with instructions that skip a step. As a result, each departure from the protocol is a reason to discount the clue count. So the first thing a defense does is compare the video to the manual, line by line.

The Eye Test Has Its Own Rules in Texas

Texas courts treat horizontal gaze nystagmus differently from the other two tests. In Emerson v. State, decided in 1994, the Court of Criminal Appeals held that HGN testimony is admissible only from an officer certified to administer the test. It also drew a hard line: a witness may not use HGN to quantify the driver’s alcohol concentration. For example, the officer can say the eyes showed six clues. However, the officer cannot say the driver was therefore at 0.10. That limit matters because juries hear the eye test as the most scientific of the three. Emerson keeps it in its lane as evidence of impairment, not a substitute for a breath or blood number.

What a Field Sobriety Test Lawyer Austin Drivers Hire Knows the Tests Miss

The battery does not measure alcohol. Instead, it measures balance, divided attention, and eye movement. Alcohol affects all three, but so do other things. For instance, age, weight, inner-ear conditions, leg or back injuries, footwear, fatigue, and nerves each move the clue count. None of that makes the tests useless as a screening tool. It does mean the clue count is a starting point, not a verdict. Under Penal Code Section 49.01, the state has to prove the driver lost the normal use of mental or physical faculties or had a concentration of 0.08. So a wobbly one-leg stand is one piece of that proof, weighed against everything else.

Refusing the Roadside Tests

Texas does not require a driver to perform field sobriety tests. The implied consent statute, Transportation Code Section 724.011, covers breath and blood specimens, not roadside exercises. Therefore, a driver who declines the tests faces no automatic license suspension for that choice alone. Still, the refusal can come into the story the officer tells about probable cause, and it does not stop an arrest. Austin’s year-round no-refusal program means a warrant for blood usually follows anyway. The tests, in other words, are one input into the arrest decision. They are not the last word on intoxication, and NHTSA never designed them to be.

How a Field Sobriety Test Lawyer Austin Courts See Uses the Video

The Austin Police Department records stops on body-worn and dash cameras, and that footage is the center of most DWI defenses in Travis County. It shows whether the officer gave the instructions in full, whether the driver was wearing boots or heels, whether the surface was level, and how long the officer actually watched the eyes. Equally, it shows the things the tests do not capture: clear speech, steady hands, a driver who followed every instruction and still picked up two clues. Lawyers play the video at the ALR hearing and, if the case goes that far, at trial. Arizona uses the same battery under its own case law, as our guide to field sobriety tests in Arizona explains.

The Bottom Line

The three standardized tests measure real things, and the clue counts have real research behind them. What they cannot do is measure alcohol directly or survive an administration that departed from the manual. Meanwhile, Emerson limits the eye test to what it can support, and the other two tests depend on conditions a roadside rarely provides. A field sobriety test lawyer Austin drivers retain is not arguing that the tests are fake. Rather, the argument is that a clue count earned on a sloped shoulder at 2 a.m. proves less than the arrest report says it does, and the video usually decides who is right.

Keep reading: Field Sobriety Test Arizona: What They Actually Measure · DUI Traffic Stop Arizona: What Officers Are Allowed to Do (and What They’re Not)

---

This article is for general informational purposes only and does not constitute legal advice. Field sobriety test evidence depends on how the tests were given, the conditions, and the video record in each case. Nothing here recommends a course of action during a traffic stop.

More guides on DUI Defense

• Arizona DUI Penalties: First Offense vs Extreme and Super Extreme DUI
• ALR Hearing Lawyer Austin: Fighting an Automatic License Suspension
• DUI Traffic Stop Arizona: What Officers Are Allowed to Do (and What They’re Not)
• DWI Lawyer Austin: What a Texas First Offense Actually Means
• Field Sobriety Test Arizona: What They Actually Measure
• San Antonio DWI Defense Attorney: How to Choose the Right One

All DUI Defense guides →