Ask Deandra: What Are the Most Common DWI Defenses in Texas?

Here is the longer answer: the nine categories, what each involves, and how they work together in a real case.

Category One: Defenses to the Stop

Under the Fourth Amendment and Article I, Section 9 of the Texas Constitution, an officer needs reasonable suspicion of criminal activity to make a traffic stop. A stop made without it violates the Constitution, and evidence obtained as a result is subject to suppression.

Whether the stop holds up is usually answered by the video rather than by the report. A report is written after an arrest, by someone who has already reached a conclusion. The footage was recorded before anyone reached anything. When the two disagree, the disagreement is itself evidence.

Common defenses to the stop:

• No traffic violation occurred. Officers normally stop drivers on the asserted basis of a traffic violation. When the body camera and dash camera footage do not show the violation, lane drift that was not drift, speeding that was not speeding, an equipment violation that did not exist, the stop is open to challenge.
• Mistaken identification of conduct. Officers sometimes read ordinary driving as a violation. Slowing for a yellow light, brief movement within a lane, or a momentary change in speed can be recorded as something it was not.
• Stops based on hunches. A stop made without articulable facts is invalid even when the hunch turns out to be right. The officer has to be able to name the specific facts that produced the suspicion.
• Defective community caretaking justifications. Stops resting on the community caretaking doctrine, a welfare check or a response to a reported disabled vehicle, have to satisfy specific requirements. Stops that exceed them are defective.
• Anonymous tip stops without corroboration. A tip about a drunk driver requires corroboration of its reliability. A bare tip does not satisfy the standard.

The detailed treatment of what to do when you are pulled over, from the driver’s perspective, appears in another post.

Category Two: Defenses to the Arrest

An officer needs probable cause to arrest for DWI. Probable cause requires more than the reasonable suspicion needed for a stop. It requires facts sufficient to warrant a person of reasonable caution in believing a crime has been committed.

Common defenses to the arrest:

• Insufficient observation evidence. Bloodshot eyes alone, odor of alcohol alone, or an admission of one drink alone are typically not enough. The officer has to combine observations into a coherent assessment.
• Conclusory probable cause statements. Officers sometimes state the conclusion without the facts underneath it. The defendant appeared intoxicated is a conclusion, not probable cause.
• Reasonable explanations for the observations. Fatigue, medical conditions, allergies, prescription side effects and the ordinary anxiety of being stopped can all explain what the officer attributed to alcohol.
• Unlawful arrest after a lawful stop. Even where the stop was good, the arrest has to rest on probable cause developed during it. An arrest made in order to investigate further, rather than on developed probable cause, is defective.

Category Three: Defenses to the Field Sobriety Tests

The Standardized Field Sobriety Tests, horizontal gaze nystagmus, walk-and-turn and one-leg stand, were validated by the National Highway Traffic Safety Administration for detecting alcohol impairment. The documented limitations are part of every DWI defense.

The argument that carries the most weight, in NHTSA’s own words

According to the NHTSA manual validation applies only where the tests are administered in the prescribed standardized manner, the standardized clues are used to assess performance, and the standardized criteria are used to interpret it. If any one element is changed, validity may be compromised. That is an argument about what the officer did, which is on the video, rather than an argument about the weather.

Common defenses to the field sobriety tests:

• The tests are voluntary. A driver who declined them has given the State no test evidence to use, and the absence of it can meaningfully weaken the case.
• Departures from standardized administration. Instructions abbreviated or skipped, the demonstration omitted, the wrong number of steps, an improperly timed one-leg stand. These go to the core of NHTSA’s own validity caveat.
• Conditions of administration. A sloping roadside, wet pavement, headlights of passing traffic and the stress of the encounter all bear on performance. Frame these as weight rather than as automatic invalidity, which is how the manual frames them.
• Individual factors. Age, weight, footwear, knee and back injuries, inner ear and neurological conditions, and medication can all affect performance independent of alcohol.
• Officer scoring errors. Scoring is observational and subjective. Officers record clues that did not occur and miss clues that did. Video review allows independent scoring.
• Non-validated tests. Finger-to-nose, modified Romberg, the alphabet and counting backwards are not part of the standardized battery and carry weaker support.
• Problems with the eye test. Horizontal gaze nystagmus requires specific administration to produce reliable results. Improper stimulus distance, passes held too long or too briefly, and failure to check for equal tracking all undermine it.

The detailed treatment of the field sobriety tests, what they are, what to expect and whether to take them, appears in our field sobriety test post.

Category Four: Defenses to the Breath Test

The Intoxilyzer 9000 is the instrument in evidential use across Texas. It is worth knowing how it got there, because it matters to the defense. The Legislature did not name it. Transportation Code Section 724.016 lets the Department adopt rules approving analytical methods, and 37 Texas Administrative Code Section 19.2 hands that job to the scientific director of the Breath Alcohol Testing Program, who certifies instruments and keeps a list. No rule names a device, and the scientific director can remove one for cause.

The fifteen minutes are about presence, not observation

37 Texas Administrative Code Section 19.3(a)(1) requires that the operator remain in the continuous presence of the subject for at least 15 minutes immediately before the test, and that the operator should exercise reasonable care to ensure the subject does not place any substances in the mouth.

Other defenses to the breath test:

• Partition ratio. Breath results in Texas are reported in grams of alcohol per 210 liters of breath, and 210 liters of breath holds the same alcohol as 100 milliliters of blood only if the person’s blood to breath ratio is exactly 2100 to 1. Where the true ratio is lower, the breath figure runs ahead of the blood concentration. Be careful with this one: the published data show mean ratios near 2380 in the post-absorptive state, which cuts the other way. Where it genuinely bites is a subject still absorbing alcohol, when the ratio can fall below 2100 to 1. Jones and Cowan, 2020.
• Medical conditions. Reflux, diabetes, ketosis from low-carbohydrate dieting and dental work have all been advanced as sources of error, with varying support. Each has to be tied to the individual client rather than asserted in the abstract.
• Instrument calibration and maintenance. Calibration records, maintenance logs and reference standard certifications are discoverable. The rule requires the reference sample result to agree with the nominal value within plus or minus 0.01 g/210 L, which gives you something concrete to check the records against.
• Operator qualifications. The operator has to be certified and current. Defective certifications and training gaps undermine the foundation for the test.

Category Five: Defenses to the Blood Test

Blood testing is forensically more complex than breath testing, and it is open to a broader range of defenses, including the two that do not travel to breath cases.

• Warrant defects. Where the specimen came from a warrant, the warrant and the supporting affidavit are fully reviewable. Defective affidavits support suppression under Franks v. Delaware or on ordinary probable cause grounds.
• Implied consent issues. Where the specimen was taken without a warrant under the implied consent chapter, the requirements of Chapter 724 have to be met. But know the boundary: in State v. Johnston the Court of Criminal Appeals held that compliance with Chapter 724 is not required where a search warrant authorizes the draw, because the question there is Fourth Amendment reasonableness.
• Who drew the blood. This is a statute, not a regulation. Transportation Code Section 724.017 lists who may take a specimen at a peace officer’s request: a physician, a qualified technician, a registered professional nurse, a licensed vocational nurse, or a qualifying paramedic or intermediate emergency medical technician. Subsection (a-1) requires only that the specimen be taken in a sanitary place. There is no rule that blood must be drawn in a hospital, and Johnston upheld a draw performed at a police station.
• The tube and the preservative. The Department’s blood kit uses grey-top tubes containing sodium fluoride as a preservative and potassium oxalate as an anticoagulant. No Texas statute or rule specifies tube contents, so a wrong-tube argument is an argument about laboratory protocol and weight rather than a per se violation. Under some conditions a specimen with absent or deficient fluoride, microbial contamination, available glucose and warm prolonged storage can generate ethanol after collection.
• Chain of custody. Gaps in the chain do not keep the blood out. In Texas, proof of the beginning and the end of the chain supports admission absent a showing of tampering or alteration, and gaps or theoretical breaches in the middle go to the weight the jury gives the result. Stoker v. State and Druery v. State. Only affirmative evidence of tampering, commingling or alteration bars admission, and the possibility of it is not enough. Chain of custody is one way of satisfying Rule 901(a), which asks only for evidence sufficient to support a finding that the item is what the State says it is. So, develop the unexplained possession periods and the labeling problems, but develop them for cross-examination and argument rather than for a motion.
• Laboratory accreditation and method validation. Here the accreditation lever does work. Under Article 38.35(d), a forensic analysis and expert testimony about it are inadmissible if the laboratory was not accredited by the Forensic Science Commission at the time of the analysis. Toxicology is an accredited discipline. Method validation documentation, accreditation status and proficiency testing records are all discoverable.
• Measurement uncertainty. Here it works too. Accreditation to ISO/IEC 17025 requires the uncertainty to be reported where it bears on conformity to a specification limit, and 0.08 is a specification limit. Department reports state the result in the form 0.095 grams plus or minus 0.005 grams per 100 milliliters.
• The analytical method. The Department’s toxicology section analyzes blood alcohol by headspace gas chromatography, typically with flame ionization detection. The methodology has known limitations that can be developed forensically.
• Drug testing methodology. In drug cases the Department screens by immunoassay to detect drug classes, then confirms specific drugs by gas chromatography mass spectrometry or liquid chromatography mass spectrometry depending on the analyte. Method validation, calibration, limits of quantitation and confirmatory testing are all subject to challenge.
• Metabolite versus active drug. In drug cases the distinction is critical. Metabolites prove past use, not impairment at the time of driving.

The detailed treatment of blood test reliability appears in our blood test post.

Category Six: Defenses to the Timing of the Test

Texas can convict on a per se theory, meaning an alcohol concentration of 0.08 or more at the time of driving. But almost no breath or blood test happens at the time of driving. The test happens at the station or the hospital, often an hour or more after the stop, and alcohol concentration does not hold still during that gap. The distance between the driving and the test is its own category of defense.

• The temporal link. The State has to supply something connecting the reported result back to the moment behind the wheel. That connection comes either from circumstantial evidence or from a retrograde extrapolation performed by the State’s expert. Where neither is developed, the per se theory has a hole in it.
• Retrograde extrapolation assumptions. An extrapolation depends on assumptions about when drinking started and stopped, how much was consumed, absorption rate, elimination rate, food in the stomach and body weight. Assumptions are inputs, not measurements. Where the expert does not have the underlying facts, the extrapolation is open to challenge and in some cases to exclusion.
• Rising blood alcohol. Alcohol takes time to absorb. A driver still absorbing at the time of the stop can be below the limit behind the wheel and above it by the time of the test. The reported number can be entirely accurate and still fail to prove the element the State has to prove.
• Assumptions that cut both ways. Extrapolating backward to a higher number assumes the driver was already eliminating alcohol at the time of driving. That has to be established rather than presumed, and the facts that would establish it are often missing from the record.

The detailed treatment appears in our Rising BAC Defense and Retrograde Extrapolation posts.

Category Seven: Defenses to Drug Recognition Evaluation (DRE)

In drug cases a Drug Recognition Evaluator may conduct a twelve-step evaluation designed to sort impairment into one of seven drug categories: central nervous system depressants, central nervous system stimulants, hallucinogens, dissociative anesthetics, narcotic analgesics, inhalants and cannabis. The protocol is presented to juries as scientific and is open to substantial challenge, but it has to be challenged on the right ground.

The ground that holds

The foundational validation studies, the Johns Hopkins laboratory work in 1985, the Los Angeles field evaluation in 1986 and the Arizona field study in 1994, validated the evaluator’s opinion against whether the drug was found in the blood or urine. That is presence, not impairment. A correct call means only that the substance was there.

The methodological critique goes further than most summaries admit. Applying a standard diagnostic-accuracy quality tool to all three studies, Kane, 2013 found spectrum bias, selection bias, verification bias, review bias and, most damaging, incorporation bias, the circular use of the very evidence the protocol is supposed to predict. The conclusion was not that the studies have limitations. It was that they do not validate the evaluation process as it is now used.

The ground that does not hold

Cannabis is often named as the protocol’s weak spot. On the published data it is the opposite. The 2021 NHTSA predictive validity study reports an overall correct classification rate of 86 percent, with cannabis at 91.3 percent and central nervous system stimulants at 74.0 percent. Peer-reviewed work on toxicologically confirmed cannabis cases found combinations of indicators performing above 96 percent. Arguing that evaluators are especially bad at cannabis invites a rebuttal that costs you the point and some credibility on the rest of the cross-examination.

Other defenses to the evaluation:

• Subjectivity in scoring. Muscle tone, demeanor, response time and pupillary reaction are all scored by judgment.
• Confirmation bias. By the time a subject reaches the evaluator, an arrest has already been made. The structural pull toward confirming the arrest decision is part of the critique in the literature.
• Training and certification gaps. Certification carries training and recertification requirements. Documentation gaps and expired certifications are discoverable.
• Combination cases. Protocol performance is weaker where more than one substance is involved than in single-substance cases.
• Timing of the specimen. Collection timing materially affects measured concentrations, which is a problem for any attempt to tie a number to the moment of driving.

The detailed treatment appears in our drug recognition expert post and our drug DWI post.

Category Eight: Procedural and Constitutional Defenses

Beyond the substantive challenges above, DWI cases involve a range of procedural and constitutional defenses.

Statements and the right to counsel

The right that governs a DWI station-house interrogation is the Fifth Amendment right, not the Sixth. Miranda supplies the warnings, Edwards v. Arizona supplies the rule that once a suspect in custody asks for a lawyer, questioning has to stop until counsel is available or the suspect reopens the conversation, and Code of Criminal Procedure Article 38.22 supplies the Texas warning and electronic recording requirements that do most of the work in practice.

The Sixth Amendment right attaches later. Under Rothgery v. Gillespie County, a Texas case, it attaches at the Article 15.17 appearance before a magistrate. In the ordinary DWI sequence, the stop, the tests, the arrest and the station-house questioning all happen before that.

And at the roadside there is usually no warning requirement at all. Under Berkemer v. McCarty a routine traffic stop is not custody for Miranda purposes, which is why roadside questioning and field sobriety tests generally proceed without warnings. The suppression fight is about what happened after the handcuffs.

Speedy trial

Texas has no speedy trial statute. The Texas Speedy Trial Act was struck down as a violation of the separation of powers in Meshell v. State in 1987, and nothing replaced it. There is no clock and no number of days.

What exists is the constitutional right, under the Sixth Amendment and Article I, Section 10 of the Texas Constitution, analyzed under the four factors of Barker v. Wingo: the length of the delay, who is more to blame for it, whether the defendant asserted the right in due course, and whether the delay caused prejudice. The Court of Criminal Appeals applies that framework to the state right as well. Zamorano v. State. The remedy is dismissal, but it is earned by balancing rather than by a calendar.

Other procedural and constitutional defenses:

• Selective enforcement. In rare cases, evidence of discriminatory enforcement can support specific defenses.
• Outrageous government conduct. Where law enforcement conduct is so egregious it shocks the conscience, due process defenses may apply. These are rare.
• Jury trial rights. The procedures around voir dire, selection and verdict are governed by protections that are defense territory.
• Prosecutorial misconduct. Brady disclosures, improper argument and related conduct issues can support remedies including dismissal.

Category Nine: Substantive Defenses to the Underlying Elements

Even when the procedural and forensic challenges fail, the State still has to prove the elements beyond a reasonable doubt.

• Operator identity. The State must prove the defendant was the person operating the vehicle. In single-vehicle accidents, multi-occupant cases and cases without direct observation, identity is a substantive defense.
• Operating. The word is not defined in Penal Code Section 49.01, but that does not mean the everyday meaning applies. Under Denton v. State the question is whether, on the totality of the circumstances, the person took action to affect the functioning of the vehicle in a manner that would enable its use. That standard is broader than driving, and it is why sleeping-in-the-car and engine-off cases are harder than clients expect rather than easier. It is still a live defense. It is just not the easy one.
• Public place. Penal Code Section 49.04 requires operation in a public place, and the definition is not in Chapter 49. It is in Section 1.07(a)(40): any place to which the public or a substantial group of the public has access, including but not limited to streets, highways and the common areas of schools, hospitals, apartment houses, office buildings, transport facilities and shops. Because the list is not exhaustive, parking lots and apartment complex drives are routinely held to be public places, which is why the private property defense fails more often than it succeeds.
• Intoxication. The State must prove either an alcohol concentration of 0.08 or higher or the loss of normal use of mental or physical faculties. Each prong is challengeable on its own merits.
• Causation in drug cases. The State must prove the substance caused intoxication, not merely that it was present in the body.

No culpable mental state

Texas DWI is unusual in having no mental state element. Penal Code Section 49.11 says that notwithstanding the general rule, proof of a culpable mental state is not required for conviction of a Chapter 49 offense, with one exception for the open container offense. That cuts both ways. It removes an element the State would otherwise carry, and it means that believing you were fine to drive is not a defense a Texas jury is permitted to act on.

The Two Motions

Everything above resolves into one of two motions, and they do different work.

If the evidence was obtained unlawfully, move to suppress it

That is the vehicle for a stop without reasonable suspicion, an arrest without probable cause, or a blood draw that was not authorized. Code of Criminal Procedure Article 38.23 is broader than the federal exclusionary rule in two ways that matter.

First, it reaches evidence obtained by an officer or other person in violation of any provision of the Constitution or laws of Texas or of the United States, so it is not limited to state actors. Second, its good faith exception is narrower than the federal one. Subsection (b) protects only an officer acting in objective good faith reliance on a warrant issued by a neutral magistrate based on probable cause. Federal law can rescue a warrant later found to lack probable cause. The Texas statute, by its own terms, cannot. And a warrantless search gets no good faith protection in Texas at all.

If the evidence is unreliable, move to keep the science out

Texas does not treat scientific evidence as automatically admissible. Under Kelly v. State, before a jury hears it the proponent, which in a DWI case is the State, must show by clear and convincing evidence that the underlying scientific theory is valid, that the technique applying the theory is valid, and that the technique was properly applied on the occasion in question.

That third requirement is the practical opening, because it is about what happened in your case rather than about whether the science works in general. The catch is that the hearing does not happen on its own. The defense has to ask for it. Cross-examination on instrument reliability is legitimate territory in Texas, and the Court of Criminal Appeals has reversed convictions where a defendant with a proper proffer was denied it. Holmes v. State.

If both motions are denied, the issue can still reach the jury

Article 38.23(a) directs that where the legal evidence raises the issue, the jury shall be instructed to disregard the evidence entirely if it believes, or has a reasonable doubt, that it was obtained unlawfully. A denied motion to suppress is not always the end of the issue.

The instruction is not automatic, and the standard is more demanding than a general dispute in the testimony. Under Madden v. State the defendant has to show three things: that the evidence heard by the jury raises an issue of fact, that the evidence on that fact is affirmatively contested, and that the contested issue is material to the lawfulness of the conduct that produced the evidence. Madden also says the dispute has to come from affirmative evidence. A cross-examiner’s questions do not create a conflict in the evidence, although a witness’s answers to them might. That sentence is the difference between getting the instruction and losing it.

See Motion to Suppress and Challenging Expert Testimony and the Kelly Hearing.

How the Defenses Work Together

Real DWI defense is not a single argument. It is a layered strategy that develops multiple defenses at once:

• The stop is challenged through a motion to suppress. If granted, the case ends.
• If the stop survives, the arrest is challenged. If granted, the case ends.
• If the arrest survives, the field sobriety evidence is challenged. Suppression or substantial impeachment weakens the State’s case.
• The chemical evidence is challenged through forensic analysis. Suppression, impeachment or contextualization can defeat or weaken the central evidence.
• The link between the test and the driving is tested separately. Even a lawfully obtained, accurate result still has to be tied back to the time of driving.
• The procedural and constitutional defenses are developed in parallel. Warnings, the right to counsel and recording requirements are addressed throughout.
• The substantive elements are kept in view. Identity, operation, public place, intoxication and causation are tracked from the beginning.

By the time the case reaches plea negotiation or trial, the defense has identified the strongest arguments and developed them through investigation, motion practice, expert consultation and discovery.

What Winning Actually Looks Like

• Dismissal. The State drops the case, usually because a successful challenge left it without evidence it needs to proceed.
• Acquittal. A jury returns not guilty. It is the only outcome that is final in your favor.
• Reduction. The charge becomes a lesser offense, which changes what appears on your record and what can be cleared later.
• A better offer. The most common practical result. A prosecutor facing a real motion evaluates the file differently than one facing none.

Three of those four are not dismissals, and that is not a consolation prize. A reduction or a materially better offer is frequently what a successful challenge actually purchases. Every outcome, including the ones that are not wins, is laid out in Every Way a Texas DWI Case Can End.

What Distinguishes a Real DWI Defense

Not every DWI lawyer develops the full range of defenses available. The features of a real defense:

• Forensic credentials. Lawyers with credentials in the science underlying chemical testing, the ACS-CHAL Forensic Lawyer-Scientist designation, advanced training in chromatography, graduate-level training in forensic toxicology, can develop chemical evidence defenses that generalists cannot.
• Body camera and dash camera review. Video review is the foundation of the stop, arrest and field sobriety defenses. Lawyers who do not watch the footage carefully miss defenses the footage would have handed them.
• Discovery completeness, and discovery timing. Full discovery includes the offense report, the footage, the chemical test records, calibration and maintenance records, certification records, laboratory accreditation and method validation records, and the administrative hearing transcript. Timing matters as much as completeness. Footage is not stored forever, and agencies overwrite it on retention schedules measured in weeks. The preservation request has to go out early rather than when a court date approaches. See Discovery and Video and Evidence Preservation.
• Motion practice. Motions to suppress are the central mechanism for producing dismissals. Lawyers who file motions are the lawyers who win suppression.
• Expert retention. Forensic toxicologists, accident reconstruction experts, medical experts and rebuttal experts on drug recognition can transform cases.
• Trial willingness. Lawyers who will not try cases lose plea leverage. Prosecutors offer better dispositions to lawyers they believe will actually try the case.

These are what distinguish a real DWI defense from routine processing toward a plea.

What If You Were Actually Drinking

Nothing above assumes you were sober. Being over the limit and the State being able to prove it beyond a reasonable doubt are two different questions, and a case can be contested on the evidence without disputing what you remember about the night.

What is left to contest is the record: whether the stop was lawful, whether the arrest rested on more than a conclusion, whether the test was properly obtained and properly performed, and whether the result says anything about the moment you were actually driving. None of that turns on how much you had to drink. Whether fighting is the right call in your situation is a separate question, walked through in Should I Fight My DWI in Texas?

The Bottom Line

Texas DWI defenses fall into nine categories: the stop, the arrest, the field sobriety tests, the breath test, the blood test, the timing of the test, drug recognition evaluation, procedural and constitutional defenses, and the substantive elements. A real defense develops as many of these as the facts support and pursues the strongest through motion practice, plea negotiation or trial.

Whether your case has strong defenses available depends on facts that require investigation, not assumption. The lawyer who treats your case as a likely plea misses the defenses that the lawyer who treats it as a contested case can sometimes develop. The right time to start the work is now.

Every Defense, In Depth

The categories above are the map. Each page below is the territory: one defense, fully developed, with the law and the science behind it. Not sure whether your case is worth fighting at all? Start with Should I Fight My DWI?

The Stop & The Arrest

The Roadside Tests

The Science of the Number

The breath and blood machinery itself (the Intoxilyzer, mouth alcohol, partition ratio, chromatography, fermentation in the tube) is covered instrument by instrument in Tests & Evidence.

The Motions That End Cases

The Elements the State Must Prove

Justification & Mitigation

Where the Fight Goes Next

DWI Defense at Deandra Grant Law

Deandra Grant Law defends DWI cases across North and Central Texas including Dallas, Fort Worth, Plano, McKinney, Frisco, Allen, Lewisville, Denton, Rockwall and Waco with the full range of defenses available. We pursue stop and arrest challenges through motion practice, forensic challenges through expert consultation and discovery, procedural defenses through trial preparation, and substantive defenses where the facts support them.

If you have been charged with DWI in Texas and want to understand the defenses available in your specific case, call Deandra Grant Law at (214) 225-7117 or schedule online for a confidential consultation. And remember that the 15-day deadline to request an administrative hearing runs from the date you received the notice of suspension.

Have a DWI question you want answered in this series? Submit it at texasdwisite.com and you might see it featured in a future Ask Deandra post.