Most people know that the legal limit for driving in Texas is .08. But there’s a second threshold that many don’t learn about until they’re sitting in jail with a DWI charge in their hand: .15. In Texas, a DWI with a blood or breath alcohol concentration of .15 or higher isn’t just a more serious version of the same charge. It’s an entirely different criminal offense category — one with mandatory consequences that kick in automatically and a level of scrutiny from the Harris County DA’s office that makes an aggressive defense more important, not less.
Here’s what you need to understand if you or someone you love is facing a DWI charge with a BAC reading at or above .15.
Why .15 Is the Magic Number in Texas
Texas Penal Code § 49.04(d) specifically addresses high-BAC DWI. A standard DWI in Texas is a Class B misdemeanor — that’s the baseline charge for a first-offense DWI with a BAC of .08 or above. But if the state can show that you had a BAC of .15 or above at the time of driving, the offense is enhanced to a Class A misdemeanor.
This isn’t prosecutorial discretion or a charging decision that varies from county to county. It’s a statutory distinction written directly into the Penal Code. The number .15 appears in the statute, and when a breath test or blood test result comes back at or above that threshold, the charge classification automatically changes.
The significance of that single letter change — B to A — cannot be overstated. It affects the maximum punishment, the mandatory conditions of any probation or sentence, and the way your case is perceived and prosecuted by the Harris County District Attorney’s office.
Enhanced Penalties: Class A vs. Class B DWI
| Consequence | Class B DWI (BAC .08-.14) | Class A DWI (BAC .15+) |
|---|---|---|
| Maximum jail time | 180 days | 1 year |
| Maximum fine | $2,000 | $4,000 |
| Mandatory ignition interlock | Not required on first conviction without specific conditions | Mandatory on conviction |
| License suspension (DPS) | 90 days to 1 year (ALR/conviction) | 90 days to 1 year (same range, but interlock required) |
| DIVERT eligibility | Eligible (if other criteria met) | Eligible but subject to heightened DA discretion |
| Employment impact | Significant | More severe; Class A misdemeanor on record |
| Immigration consequences | Potentially significant | Higher risk of adverse immigration outcome |
The Mandatory Ignition Interlock Requirement
One of the most significant and immediate consequences of a .15+ BAC reading is the mandatory ignition interlock requirement. Under Texas Transportation Code § 521.2461, if a person is convicted of DWI with a BAC of .15 or higher, the judge must require the installation and use of an ignition interlock device as a condition of any probation, and the person’s driver’s license must be endorsed with the interlock requirement.
This isn’t optional. The judge doesn’t have discretion to waive it. If you’re convicted, the interlock goes on your car. Every vehicle you operate must have one installed. The device requires a clean breath test to start the car and periodic rolling retests while driving. The duration of the interlock requirement varies, but it is typically required for the length of any probation period — up to two years for a Class A DWI.
The interlock requirement extends beyond just the criminal case. The DPS license endorsement means that even if you get an occupational driver’s license during suspension, that ODL will require interlock compliance. Once you’re convicted with a .15+ reading, the interlock follows you through every stage of the license process until the requirement expires.
How Harris County Prosecutes High-BAC Cases
The Harris County District Attorney’s office takes a harder line on .15+ cases. Herman spent years working in that office, and he understands how prosecutors evaluate these cases from the inside.
High-BAC cases get flagged early. A DWI charge with a reported BAC nearly twice the legal limit or higher draws attention at the charging stage. Prosecutors are less likely to offer favorable plea deals, more likely to push for higher penalties, and — particularly with very high readings — more likely to use the BAC number as a rhetorical centerpiece of the case.
Jurors also react differently to high BAC numbers. A .09 BAC case is close enough to the legal limit that jurors may have reasonable doubt about impairment. A .20 or .25 BAC is a number that can provoke an emotional reaction. Herman accounts for this in his trial strategy when cases go to a jury, and it affects how he structures plea negotiations when that’s the appropriate path.
The Harris County DA’s office also scrutinizes DIVERT applications more carefully for high-BAC cases. While .15+ BAC cases are not categorically excluded from DIVERT, the DA exercises more discretion in approving them, and very high BAC readings may result in DIVERT being declined. This is something Herman addresses directly with the DA’s office when pursuing DIVERT on behalf of high-BAC clients.
Why High BAC Results Are Often More Vulnerable, Not Less
This is counterintuitive — and it’s one of the most important insights that comes from Herman’s experience on both sides of these cases.
People assume that a very high BAC reading means the case is stronger for the prosecution. In some ways it is. But in other ways, high BAC results create their own vulnerabilities that an experienced DWI defense attorney can exploit. Here’s why:
Retrograde Extrapolation Problems
The BAC reading reflects what was in your blood at the time of testing — not necessarily at the time of driving. Alcohol absorption and elimination rates vary based on body weight, food consumption, rate of drinking, and individual metabolism. A blood draw taken 90 minutes after you were last driving can reflect a very different BAC than what existed while you were operating the vehicle. If the BAC was rising at the time you drove, you could have been below .15 when driving even if you were above it when tested. This is called “retrograde extrapolation,” and it’s a legitimate scientific defense challenge.
Testing Machine Errors Are Amplified
Every breath testing device — including the Intoxilyzer 9000 used in Texas — has a margin of error. DPS acknowledges that the instrument has a potential error rate. When a result is close to .15 (say, .15 or .16), even a small margin of error could push the true result below the threshold. This doesn’t make the case disappear, but it creates doubt about whether the Class A enhancement is truly warranted. For blood tests, the margin of error is different but the same principle applies — laboratory testing has variance, and chain of custody issues can contaminate the integrity of the result.
Physiological Factors That Affect Readings
Breath testing is an indirect measure. The machine doesn’t test your blood; it tests your breath and uses a conversion factor to estimate your BAC. That conversion factor (the partition ratio) is assumed to be 2100:1 for the entire population — but research shows significant individual variation. People with higher body temperatures, certain lung conditions, or other physiological factors can produce breath results that overstate their actual BAC. The higher the reported number, the more significant this margin of error becomes in absolute terms.
Chain of Custody Issues in Blood Tests
Many .15+ cases involve blood testing rather than (or in addition to) breath testing. Blood draws require proper collection, handling, storage, and laboratory processing. Any break in the chain of custody — an improperly labeled sample, a storage condition that allowed fermentation, an unqualified analyst — can compromise the reliability of the result. The higher the reported BAC, the more likely it is that close examination of the laboratory procedures will reveal issues. Herman’s examination of breath and blood test evidence in high-BAC cases is thorough and detailed.
Defense Strategies That Work for High-BAC Cases
High-BAC DWI defense requires a layered approach that addresses both the scientific evidence and the courtroom dynamics. The strategies Herman employs include:
Challenging the traffic stop. If the stop was unlawful, everything that follows — including the BAC test — can be suppressed. Even in high-BAC cases, the stop has to be legal. If it wasn’t, the case ends there.
Scientific expert witnesses. High-BAC cases often benefit from expert testimony from toxicologists who can explain to a jury the limitations of breath and blood testing, retrograde extrapolation science, and individual physiological variation. Herman works with qualified expert witnesses when the case warrants it.
Attacking the blood test chain of custody. For blood cases, this means obtaining all laboratory documentation, examining the credentials of the analyst, reviewing storage conditions, and looking for any procedural deviation that could compromise the result.
Timeline reconstruction. Establishing a precise timeline of when and what the client consumed, when they stopped drinking, and when they drove can support a retrograde extrapolation argument that the BAC at the time of driving was below the level the test suggests.
Negotiating on the enhancement threshold. In some cases, there may be sufficient doubt about whether the BAC truly reached .15 — due to machine error, physiological factors, or timing — to support a negotiated reduction of the charge from Class A back to Class B. This is not guaranteed, but it is a realistic goal in appropriate cases.
The Stakes Are Higher — So Is the Need for the Right Attorney
A Class A DWI is not just a footnote. It is a more serious conviction, with more serious consequences, prosecuted more aggressively. The year in county jail as a maximum sentence is real. The mandatory ignition interlock is real. The difficulty of ever having this conviction treated as anything less than what it is — that’s real too.
This is not the situation for cutting corners on your legal defense. The same DWI defense strategies that apply to standard cases need to be applied with even more rigor when a .15 reading is what you’re up against. And the attorney you hire needs to have the experience, the relationships, and the scientific knowledge to challenge the evidence effectively.
Don’t Accept the .15 Reading at Face Value
Herman Martinez has seen breath and blood test results challenged, reduced, and thrown out in cases that looked airtight on paper. A number on a printout from a machine is not proof beyond a reasonable doubt — not when that machine has known limitations, the testing was performed by a human who can make errors, and the science of toxicology offers legitimate challenges to what the number actually means.
If you’re facing a DWI charge with a BAC of .15 or higher in Houston or Harris County, call Herman at (713) 242-1779 for a free, confidential case evaluation. The higher the stakes, the more important it is to have the right attorney fighting for you from the very beginning. You can also request a free online case evaluation to get started today.
