How Police Determine Impairment in Texas DWI Stops

Police officers in Texas determine impairment using three main tools: how you drive and behave, standardized field sobriety tests (SFSTs), and chemical tests such as breath or blood. Standardized field sobriety tests (SFSTs) are a set of three balance and coordination tests developed by the National Highway Traffic Safety Administration that officers use on the roadside to look for signs that alcohol or drugs are affecting your mental and physical abilities.

If you were just stopped in Houston or another Texas county and you are trying to figure out what happened and what comes next, this guide breaks down what officers look for, how SFSTs work, where they can be wrong, and what that means for your license, job, and case.

Big Picture: How Do Police Officers Determine If Someone Is Impaired?

Texas DWI law focuses on whether your “normal use of mental or physical faculties” is impaired by alcohol, drugs, or a combination. To make that call, most officers walk through the same general steps:

• They observe your driving, such as speeding, swerving, or braking late.
• They talk with you at the window and note your speech, coordination, and responses.
• They may ask you to step out and perform standardized field sobriety tests.
• They may offer or request a roadside breath test.
• If they arrest you, they request an official breath or blood test for alcohol and sometimes drugs.

For someone in your shoes, it can feel like the officer has already made up their mind. But each step has rules and limits. Understanding those rules is the first way to protect your license, your work as a provider for your family, and your finances.

For a deeper dive into what officers look for during a traffic stop and SFSTs, you can review a step-by-step pull-over guide focused on Texas DWI stops.

What Are Standardized Field Sobriety Tests (SFSTs)?

When people ask, “What are standardized field sobriety tests (SFSTs)?”, they are usually talking about three specific tests:

• Horizontal Gaze Nystagmus (HGN)
• Walk-and-Turn
• One-Leg Stand

These were developed through studies funded by the federal government. The idea is that if officers give the tests the same way every time, they can compare your performance to known patterns of impairment. In reality, weather, nerves, medical issues, and how carefully the officer follows the instructions all affect the results.

If you are a project superintendent or crew manager who spends long days on your feet, you may already be tired, sore, or dealing with old injuries. That reality does not always match the textbook version of these tests.

For an even more technical breakdown of the science behind these tests and breath machines, including studies on accuracy, you might review a detailed look at field sobriety test accuracy.

HGN: The Eye Test

In the Horizontal Gaze Nystagmus test, the officer holds a pen or light in front of your eyes and moves it side to side. They watch for “nystagmus,” which is a jerking movement of the eyes. Alcohol and some drugs can make this more obvious at certain angles. The officer scores six possible “clues,” three in each eye. The more clues they say they see, the more they think you are impaired.

Problems arise because many other things can cause eye jerking or eye tracking problems: inner ear issues, past head injuries, some medications, contact lenses, or just nerves and bright lights. If you are on a dark roadside in Harris County with flashing red and blue lights in your face, it is not a calm testing environment.

For readers who want more detail on this specific test, another article explains why HGN can produce misleading signs of impairment, especially when viewed later on body camera or dash camera video.

Walk-and-Turn: Divided Attention on a Line

In the Walk-and-Turn, the officer asks you to take nine heel-to-toe steps on a line, pivot, and come back. While you do it, they watch for eight possible “clues,” including whether you start too soon, step off the line, miss heel-to-toe by more than half an inch, raise your arms, or turn incorrectly.

Think about when you last walked heel-to-toe in a straight line, in boots or work shoes, on gravel, in the dark, with traffic flying by. This test measures “divided attention,” your ability to follow instructions and maintain balance. It does not account very well for bad knees, back problems, uneven surfaces, or simple anxiety.

One-Leg Stand: Balance on a Clock

In the One-Leg Stand, you raise one foot about six inches off the ground and count in a certain pattern until the officer tells you to stop, usually for about 30 seconds. The officer looks for swaying, hopping, putting your foot down, or using your arms to balance.

Again, this test demands balance, core strength, and focus. A construction manager who spent 10 hours on a job site in steel-toe boots may be shaky on a good day, with no alcohol at all. That does not always line up neatly with what the paperwork later claims.

Can You Fail a Field Sobriety Test Even If You Are Sober?

Yes, you absolutely can “fail” a field sobriety test even if you are sober. The tests do not measure alcohol directly. They measure balance, coordination, and ability to follow directions under stress.

Common reasons sober people look impaired on SFSTs include:

• Fatigue after a long workday or night shift
• Old injuries to ankles, knees, hips, or back
• Inner ear problems or vertigo
• Being overweight, out of shape, or simply not athletic
• Uneven or sloped pavement on the roadside
• Nerves, anxiety, or panic attacks
• Language barriers or hearing issues, especially in noisy traffic

Micro-story: Picture this. A 36-year-old site manager is driving home from a late concrete pour in northwest Houston. He has one beer with the crew before leaving. On the way home, he drifts slightly over the lane marker while changing the radio. A trooper pulls him over. On camera, he looks tired and sunburned. He steps out in heavy boots, on gravel near a ditch, with cars flying by. He struggles through the Walk-and-Turn because his back is tight and his legs are exhausted. The officer checks several clues and arrests him for DWI. His performance on the tests may say more about exhaustion and conditions than about one beer.

If you are worried that a bad knee, lack of sleep, or simple nerves made you look worse than you were, that is a valid concern, not an excuse. The details of the scene, your medical history, and the officer’s instructions all matter later.

Can Fatigue or Medical Conditions Mimic Signs of Intoxication?

Yes. Fatigue and many medical conditions can mimic the same signs officers are trained to look for as intoxication. That includes bloodshot eyes, slow or slurred speech, trouble balancing, or delayed responses.

Some examples:

• Fatigue and sleep deprivation can cause droopy eyelids, delayed responses, and poor coordination. A foreman coming off a 14-hour shift on a Houston job site may look and feel worse than someone who had several drinks but slept well.
• Diabetes and blood sugar swings can cause confusion, glassy eyes, and even an acetone-like smell on the breath that some officers mistake for alcohol.
• Inner ear problems affect balance and can make walk-and-turn or one-leg stand tests almost impossible.
• Neurological conditions or past concussions can change the way your eyes move on the HGN test.
• Prescription medications can cause drowsiness or unsteady gait even when taken exactly as directed.

For a Professional License Worrier working as a nurse, this overlap can be especially scary. You may know that your medical condition or prescribed meds affect your balance or speech, yet you still worry that a DWI allegation could trigger board questions. Documenting your diagnosis and medications and getting accurate legal advice early can help you prepare for both the criminal case and any licensing concerns.

What Are the Legal Limits for Drug-Related DWIs in Texas?

Most people know the alcohol limit, 0.08 blood alcohol concentration for adults, but drug-related DWIs in Texas work differently. There is no single legal number for most drugs. Instead, the law focuses on whether a substance has affected your “normal use of mental or physical faculties.”

That means you can face a DWI charge if officers and prosecutors claim that:

• You took illegal drugs such as cocaine, meth, or THC, or
• You took prescription drugs like painkillers or anxiety medication, even with a valid prescription, and
• Those substances affected how you drove or how you performed on SFSTs.

In some cases, blood tests measure levels of specific drugs. But the science around how those numbers connect to real-world impairment is far less developed than alcohol. This is where training and testimony of special officers called DREs, or Drug Recognition Experts, often come into play.

If you are an Analytical Planner, this is the area where scientific limits and defense strategies become very important. How your blood was drawn, stored, and tested, and whether the officer followed proper DRE protocols can change how strong or weak the evidence looks.

What Are “DRE Officers” and How Do They Determine Drug Impairment?

DRE stands for Drug Recognition Expert or Drug Recognition Evaluator. These are officers who complete extra training to evaluate drivers suspected of being under the influence of drugs rather than (or in addition to) alcohol.

A DRE evaluation usually includes:

• Review of the driving behavior and SFST results
• Questions about medical history and drug use
• Checking pulse, blood pressure, and body temperature
• Detailed eye exams, including different forms of nystagmus testing
• Checking muscle tone and signs of injection sites
• Divided attention tests beyond the standard SFSTs
• Requesting a blood or urine test for lab confirmation

DRE officers categorize signs into drug “families,” such as depressants, stimulants, hallucinogens, or narcotic analgesics. The problem is that some of their charts and conclusions are based on patterns and training rather than individualized medical evaluations. Two different conditions can look very similar to a DRE, especially in a stressful roadside or station setting.

For a Savvy High-Net-Worth reader, this is often where legal arguments focus. The question is not just what the DRE concluded, but whether their evaluation method is truly reliable, whether they followed the required 12-step process, and whether any of their opinions can be limited or challenged before trial.

What Happens If You Refuse a Sobriety Test in Texas?

Refusing tests in Texas is not a simple “yes or no” issue. There are actually several different types of tests:

• Voluntary roadside SFSTs like HGN, Walk-and-Turn, and One-Leg Stand
• Portable roadside breath tests (handheld devices)
• Official breath or blood tests requested after an arrest

You generally have the right to refuse SFSTs and a roadside portable breath test. However, Texas has an “implied consent” law for official breath and blood tests after you are arrested. If you are lawfully arrested for DWI, the officer will read you warnings and ask for a breath or blood sample. Refusing that official test can trigger an automatic driver’s license suspension, even if your DWI charge is later reduced or dismissed.

For more legal detail, you can review the statutes that explain Texas implied-consent law and chemical test rules, including how refusals are handled statewide.

ALR: License Consequences After Refusal or Failure

In Texas, the Administrative License Revocation (ALR) process is separate from your criminal DWI case. If you refuse an official breath or blood test, or if you take it and the result is at or above 0.08, the officer will usually confiscate your license and give you a temporary permit. You then have a limited time, typically 15 days from the date you receive the notice, to request an ALR hearing to challenge the suspension.

Missing that deadline can lead to a suspension that lasts months, which is a serious problem if you drive for work, travel between job sites, or support a family. For clear step-by-step information about how ALR hearings and refusal timelines affect your license, you can review a guide focused on the Texas ALR process.

The Texas Department of Public Safety also offers a Texas DPS overview of the ALR license-suspension process, which explains the basic timelines and hearing procedures.

Practical ALR Checklist for Someone in Your Shoes

If you were just arrested in Harris County or a nearby county and refused or failed a test, here is a simple, practical checklist:

• Look at the temporary driving permit or notice the officer gave you and note the date.
• Mark a date on your calendar 15 days from that notice, so you know the usual deadline for requesting an ALR hearing.
• Write down everything you remember about the stop, the SFSTs, and the test request while it is still fresh.
• Gather any medical records, prescriptions, or work schedules that may explain fatigue or physical limitations.
• Talk with a qualified Texas DWI lawyer as soon as possible so they can help file the ALR hearing request and review your options.

For a Career-Focused Executive, these deadlines and the possibility of a public license suspension can feel like the biggest threat. Early action, quiet preparation, and careful handling of both the criminal case and ALR hearing are crucial to protecting your driving record and professional reputation.

Can a Police Officer’s Bias Influence a DWI Arrest?

Officers are trained to be neutral, but they are still human. Bias can influence how they interpret your behavior, how they score your field sobriety tests, and even how they write their reports.

Some common bias issues include:

• Focusing only on signs that confirm their suspicion you are impaired, while ignoring signs that you are sober
• Scoring SFSTs harshly because you questioned their instructions or showed frustration
• Letting the time of night, the neighborhood, or your appearance color their judgment
• Assuming tired or nervous behavior must mean you are intoxicated

This is where video evidence, cross-examination of the officer, and comparison with SFST manuals can matter a lot. For example, if the video shows you generally steady and polite, but the officer’s report claims you were swaying heavily and slurring your speech, that gap can be important in negotiations or at trial.

If you are the Casual Unaware type of reader who never thought much about this until you or a friend were pulled over, it is helpful to know that the officer’s opinion is not the final word. There are ways to question and test that opinion in court.

Field Sobriety Tests, Breath Tests, and Common Myths

There are a lot of myths about DWIs in Houston and across Texas. Some of the most common include:

• Myth: “If I perform well on SFSTs, I cannot be arrested.”
  Reality: Officers can still arrest based on their overall observations, even if you think you did fine on the tests.
• Myth: “Refusing every test will always help my case.”
  Reality: Refusal can help in some ways, but it also triggers ALR consequences and can be argued as “consciousness of guilt” at trial.
• Myth: “If my BAC is under 0.08, I am automatically safe.”
  Reality: Texas can still prosecute DWIs under 0.08 if they claim your faculties were impaired.
• Myth: “A DWI in Harris County is just a traffic ticket.”
  Reality: A first-time DWI is a criminal offense that can bring fines, license suspension, and possible jail time.

For the Analytical Planner, one key point is that no single piece of evidence decides your case by itself. SFSTs, videos, officer reports, breath or blood tests, and your medical history all interact. That also means there are multiple places where errors, weak spots, or reasonable doubts may exist.

Key Questions & Evidence Limits for the Analytical Planner

If you like to think in checklists and evidence trees, here are some questions that often matter for technically minded readers:

• Did the officer have a valid legal reason to stop you in the first place, such as a specific traffic violation?
• Did they follow the standard SFST instructions and demonstrate each test correctly?
• Was the SFST area level, dry, and reasonably safe, or were there obvious hazards?
• Did the officer ask about your medical conditions, injuries, or footwear before grading your performance?
• Was the breath machine properly maintained and calibrated, with up-to-date records?
• For blood tests, was the sample collected, stored, and tested using accepted forensic standards?

Each “yes” or “no” here can affect how strong the state’s case looks and what defense options might exist. For some readers, an interactive Q&A resource for common DWI procedure questions can be helpful to explore these issues in more depth before speaking with a lawyer about your specific facts.

Discreet Concerns for the Career-Focused Executive

If you are a Career-Focused Executive, your main worries may not be just fines or a short license suspension. You may be focused on business travel, professional reputation, background checks, and what your employer or board might see.

A few points to keep in mind:

• Many first-time DWIs in Harris County start in county criminal courts, not traffic court. The process can span several months or longer.
• Court settings and hearings are public records, but many busy professionals handle them quietly by arranging schedules, coordinating with counsel, and using remote appearances when allowed.
• The strength of the SFST and breath or blood evidence often shapes whether your case can be negotiated to a reduced charge or alternative resolution.
• Timely action on ALR can preserve your ability to drive to work while the criminal case is pending.

Discretion usually comes from planning and control, not from ignoring deadlines. The more you understand about what the officer did and why, the better you can work with counsel to manage both the legal and professional fallout.

Top FAQs About What Are Standardized Field Sobriety Tests (SFSTs)? Under Texas Law

Can SFST results alone prove I was legally intoxicated in Texas?

SFST results alone are usually not the only evidence, but officers and prosecutors often use them as a major part of their case. In many Harris County DWIs, SFSTs work together with driving behavior, officer observations, and any breath or blood test. Weaknesses in how the tests were given or scored can be important in challenging the overall claim of impairment.

How do SFSTs affect my DWI case in Houston if I have medical issues?

If you have medical issues that affect balance, coordination, or eye movements, that should be taken into account. Documentation from your doctor, prescription records, and any mention of your condition in the police video can help show why your SFST performance may not equal intoxication. This is especially important for Houston drivers who work physical jobs or have chronic conditions.

What happens in Texas if I refuse the breath or blood test after SFSTs?

Refusing an official breath or blood test after SFSTs usually triggers an ALR case and a potential license suspension, even before your criminal case is finished. You typically have about 15 days from the notice to request a hearing and fight that suspension. The refusal itself can also be mentioned by the prosecution in court as evidence that you were worried about the results.

Can fatigue from work make me fail SFSTs in Harris County?

Yes, fatigue from a long workday can make it harder to balance, follow fast instructions, or remember counting patterns on SFSTs. Many Houston and Harris County drivers are stopped late at night after shift work or overtime when they are already exhausted. In those cases, videos, work records, and witness statements can help explain why your performance looked worse than your actual level of alcohol or drug use.

Are SFSTs required in every Texas DWI stop?

No, SFSTs are not required in every DWI stop, although many officers prefer to give them. Some drivers cannot safely perform the tests due to age, injury, or disability, and officers may skip or modify the tests in those situations. The lack of SFSTs does not automatically mean your case will be dismissed, but it can change how strong the state’s impairment evidence appears.

Why Acting Early After a Texas DWI Stop Matters

If you are reading this soon after a traffic stop in Houston or another Texas county, it is normal to feel overwhelmed. You might be replaying every moment, from the flashing lights to the eye test and walking on the line, wondering how much damage has already been done to your job, your license, and your finances.

Here are some realistic next steps that can help:

• Write down your memory of the stop and tests while it is still fresh. Include where you were, what the officer said, how the ground felt, what you were wearing, and how tired or injured you were.
• Gather your medical records and prescriptions that may explain any balance, coordination, or eye issues.
• Check your ALR deadline so you do not miss the chance to fight a license suspension.
• Stay off social media when it comes to discussing the incident. Casual posts can be misunderstood or used out of context.
• Consult a qualified Texas DWI lawyer who can review the SFSTs, video, and test results with you and explain the specific options in your case.

Getting informed early does not guarantee a particular outcome, but it puts you in a far better position than waiting and hoping things sort themselves out. Knowledge about SFSTs, chemical tests, and the ALR process is one of the best tools you have to protect your role as the practical, worried provider for your family.

If you prefer to learn by watching rather than reading, this short video explains how Texas field sobriety tests are supposed to work, why so many people “fail” even when they are trying their best, and what steps you can take to document your side of the story and protect ALR deadlines.

Butler Law Firm - The Houston DWI Lawyer
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