If you’re wondering whether field sobriety tests are actually accurate or if they can be successfully challenged in court, you’re asking the right questions. The truth is, field sobriety test accuracy is a joke — these tests are fundamentally flawed, completely subjective, and nearly impossible to pass even when you’re stone-cold sober.
Here are the major accuracy issues that plague field sobriety tests:
- They’re designed for failure
- Completely subjective scoring
- Medical conditions skew results
- Environmental factors are ignored
- Officer training is inadequate
- No standardization in real-world conditions
- Age and physical limitations are often overlooked
The bottom line? Field sobriety tests are pseudoscientific garbage that prosecutors love to use because they can be very convincing for juries. But here’s what they don’t want you to know: these tests can be beaten in court when you have an attorney who understands the science behind them.
Mark Thiessen is a board-certified ACS-CHAL Forensic Lawyer-Scientist — the highest honor awarded to attorneys by the American Chemical Society. He’s secured over 100 Not Guilty verdicts and thousands of dismissals by exposing exactly these kinds of flaws. If you’re facing DWI charges based on field sobriety test results, don’t let junk science ruin your future. Call Thiessen Law Firm today at (713) 864-9000 and let us show you how to fight back and win.
What are the three standard field sobriety tests?
The three standard types of Texas sobriety tests, all developed by the National Highway Traffic Safety Administration (NHTSA), include:
- The horizontal gaze nystagmus test (HGN)
- The walk and turn test
- The one-leg stand test
It’s worth noting that these are the only three “sanctioned” field sobriety tests. If an officer asks you to do something like recite the alphabet backwards or count to 100, those aren’t official tests — they’re just fishing expeditions hoping you’ll say something incriminating like “I can’t even do that sober.” Don’t fall for it. Even if you stumble through them perfectly, the officer can still find reasons to arrest you based on their “observations” of your performance.
Continue reading: Can you refuse a field sobriety test?
Are field sobriety tests accurate? Here are 7 reasons they’re NOT.
1. They’re designed for failure
Field sobriety tests aren’t created to give you a fair shot at proving your sobriety — they’re engineered to collect evidence against you. The field sobriety test instructions are so rigid and unnatural that they set you up to fail from the start.
Take the walk-and-turn test: when was the last time you walked heel-to-toe in a straight line with your arms glued to your sides? Never, because that’s not how humans naturally walk. The one-leg stand requires you to balance motionless for 30 seconds — something that would challenge a gymnast under perfect conditions, let alone someone standing on the side of a highway with cars flying by.
The scoring criteria are equally brutal. In the horizontal gaze nystagmus test, officers are looking for tiny eye movements measured in millimeters, and any deviation gets marked as a “clue” of intoxication. For the walk-and-turn, you can fail for starting too early, stopping for any reason, raising your arms for balance, or taking the wrong number of steps. These aren’t reasonable standards — they’re traps designed to generate probable cause for DWI arrest regardless of your actual level of impairment.
2. Completely subjective scoring
Here’s the dirty secret about field sobriety tests: there’s no objective measurement involved. Officers are literally eyeballing your performance and calling it science. During the horizontal gaze nystagmus test, an officer shines a flashlight in your face and claims they can detect impairment by watching for microscopic eye jerking movements. They’re making split-second judgments about neurological responses while standing on a dark roadside — and this guesswork becomes “evidence” in court.
These determinations are entirely up to the officer’s interpretation, and that interpretation is heavily influenced by their preconceived notion that you’re guilty. The same performance that one officer might consider acceptable could be deemed a failure by another. This isn’t science — it’s opinion dressed up as expertise.
3. Medical conditions skew results
Countless medical conditions can cause you to fail field sobriety tests even when you haven’t had a drop to drink. Inner ear problems, vertigo, back injuries, knee problems, hip issues, and neurological conditions all affect balance and coordination. The horizontal gaze nystagmus test is particularly problematic because dozens of medical conditions can cause natural eye jerking that has nothing to do with alcohol consumption.
Additionally, people with learning disabilities, ADHD, or other cognitive conditions may struggle to process and follow the complex field sobriety test instructions, leading to performance issues that get misinterpreted as signs of impairment.
4. Environmental factors are ignored
Field sobriety tests were designed for controlled laboratory conditions, but they’re administered on the side of busy highways in terrible conditions. Try balancing on one leg while eighteen-wheelers roar past at 70 mph, creating wind gusts and distracting noise. Attempt to walk heel-to-toe on uneven pavement, gravel, or grass while wearing dress shoes or high heels. Follow an object with your eyes while police car emergency lights are flashing directly in your face and oncoming headlights are creating additional visual chaos.
Weather conditions make these tests even more unreliable. Rain, snow, ice, and strong winds all affect your ability to maintain balance and follow instructions. Poor lighting conditions make it difficult to see where you’re supposed to walk or what object you’re supposed to follow. Officers don’t adjust their expectations based on these environmental challenges — they simply mark down every struggle as evidence of intoxication, regardless of the obvious external factors affecting your performance.
5. Officer training is inadequate
Most police officers receive minimal training on field sobriety test administration, and many don’t understand the scientific principles behind the tests they’re conducting. They learn basic procedures in a short training course, but they’re not taught about the numerous medical conditions, medications, and environmental factors that can affect test results. This lack of understanding leads to misinterpretation of normal responses as signs of impairment.
The training problem extends to non-standardized field sobriety tests as well. Officers sometimes improvise their own tests or use outdated methods that have no scientific backing whatsoever. They might ask you to count backwards, recite the alphabet, or touch your nose — none of which are validated sobriety tests. Yet these improvised examinations often carry the same weight in their decision to arrest you.
6. No standardization in real-world conditions
The three standardized field sobriety tests were developed under controlled laboratory conditions with specific lighting, flooring, and environmental parameters. In the real world, officers administer these tests on highway shoulders, in parking lots, on sidewalks, and in all kinds of weather conditions that bear no resemblance to the controlled environment where the tests were validated.
This lack of standardization extends to how officers explain and demonstrate the tests. Some officers rush through the instructions, others provide incomplete demonstrations, and many fail to give you adequate time to understand what’s expected.
The field sobriety test for drugs presents additional complications because the same tests used to detect alcohol impairment are applied to drug impairment, despite different substances affecting coordination and eye movement in completely different ways. This one-size-fits-all approach ignores the fundamental differences in how various substances affect human performance.
7. Age and physical limitations are often overlooked
People over 60 have significantly more difficulty with balance-based tests, not because they’re intoxicated, but because aging naturally affects equilibrium and coordination. Officers rarely account for these age-related changes when scoring field sobriety tests. Similarly, people with physical disabilities, previous injuries, or chronic conditions face unfair disadvantages that have nothing to do with alcohol consumption.
You might wonder why cops do field sobriety tests instead of breathalyzers if breath tests are more accurate and objective. Refusing a breathalyzer in Texas triggers automatic license suspension, so officers often use field sobriety tests as a preliminary assessment tool, but the real answer is that field sobriety tests give officers a more compelling story to use against you in court.
Field sobriety test accuracy issues — FAQs
What makes a field sobriety test invalid?
A field sobriety test becomes invalid when officers fail to follow proper procedures, conduct tests under improper conditions, or ignore medical factors affecting performance. If you have a failed field sobriety test due to medical conditions, age-related factors, or environmental issues rather than alcohol impairment, the results should be considered invalid evidence.
Do field sobriety tests hold up in court?
Field sobriety tests can be challenged and beaten in court when you have an attorney who understands their scientific flaws. Experienced DWI lawyers routinely dismantle field sobriety test examples by highlighting improper administration, environmental factors, and subjective scoring to show juries why these results don’t prove intoxication beyond a reasonable doubt.
Why do cops do field sobriety tests instead of breathalyzers?
Officers use field sobriety tests because they provide more subjective “evidence” that can be interpreted multiple ways in court, unlike breathalyzer results which give specific numerical readings. These tests can be administered immediately without equipment and help officers build probable cause for arrest, especially in drug impairment cases that wouldn’t show up on a breathalyzer.
Need help fighting a DWI charge? Contact Thiessen Law Firm.
Because of field sobriety test accuracy issues, failing a field sobriety test is not the end of the world. In fact, if you have a decent lawyer at your side, a failed field sobriety test could mean absolutely nothing in court. Problems with field sobriety tests can work in your favor.
Thiessen Law Firm’s Triple Board Certified Lawyer-Scientist Mark Thiessen has successfully achieved over 100 Not Guilty verdicts and thousands of dismissals for clients in difficult positions like yours.
Looking to protect yourself against overzealous police work and junk sciene? Thiessen Law Firm is the go-to law firm for DWI in Houston. If you’d like to learn more about how to fight back against a failed field sobriety test that resulted in a DWI charge, call us at (713) 864-9000 or fill out our online form today.
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