The legal limit is .08. This means a driver is guilty of DWI if his blood alcohol concentration (BAC) is .08 or greater at the time of driving. Courts call this the per se (in itself) theory of DWI. But this theory creates two issues.

First, the law requires drivers arrested for DWI to cooperate with police. In other words, the driver must either provide a breath test or face a longer driver’s license suspension. Further, this breath test measures the driver’s BAC. And prosecutors use the test results to convict drivers of DWI. As a result, many drivers understandably decline to provide a breath test.

Second, BAC tests raise accuracy issues. A person is guilty if he is intoxicated “while operating a motor vehicle in a public place.” Thus, a driver must be drunk at the time of driving and not at the time of the test. Otherwise, he is not guilty of DWI.

But there is a time gap between the time of the DWI arrest and the time of the BAC test. This time gap varies. Sometimes it is only twenty minutes. Other times it is longer than 1.5 hours. As a consequence, the test may not accurately reflect the driver’s BAC level at the time of driving.

And this can cause an innocent person to go to jail when the driver is barely over the DWI legal BAC limit. A driver with a BAC of .09, .10, .11, .12, or .13 should look at this issue carefully. This is the splash zone for jury trials. Especially if there is a good arrest video and the client presents well. A driver in this position may want to push his or her case to trial.

But to see how these problems arise, we first need some historical context.

Texas DWI Crimes and the Supreme Court.

DWI is mostly a state crime. For instance, if S.A.P.D. arrests you for a first-time DWI in San Antonio, then the local prosecutor will handle your case. If a judge or jury convicts you of DWI, then they may give you probation or send you to either the county or state jail.

However, there is one exception to this rule. DWI arrests on federal property are federal crimes. This means you will go to federal court instead of the local courthouse. But federal DWI cases are not as common as state DWI cases.

Nonetheless, the Supreme Court frequently weighs in on DWI topics. This is surprising because DWI is mostly a state crime and the Supreme Court usually deals with federal issues. Yet, it also shows how big a problem DWI is in America.

To combat the problem of DWI, state legislatures are passing tougher laws. They are requiring drivers to give blood draws–even on first-time DWI arrests. And they are passing higher penalties for not providing a breath test. Lawmakers say these laws protect the public from the danger of drunk drivers.

But sometimes the DWI laws go too far. And this requires the Supreme Court to balance the need for public safety against our individual rights to be free from unlawful searches and seizures.

More recently, Justice Samuel Alito has taken the lead on DWI issues at the Supreme Court. His opinions provide helpful context on the history of DWI and Implied Consent laws in America.

The problem of drunk driving started at the dawn of the vehicle age. Consequently, New Jersey passed one of the earliest DUI laws in America. But this law was crude. And it did not contain a BAC limit. Nevertheless, other states passed similar DUI laws.

Unfortunately, people continued to drive drunk. Accordingly, states refined their DUI laws. In 1939, Indiana passed the first law with a DWI legal BAC limit. The limit was .15. But at the same time, this limit was only a presumption. This meant defendants could challenge the limit at trial. In the same manner, other states passed laws with DWI legal BAC limits.

Later, states lowered the DWI legal BAC limit from .15 to .10. Then they lowered it again. This time it went from .10 to .08. In addition, states moved from a presumption to a per se definition of DWI. And this is the current law in Texas.

Yet, these BAC laws raised two questions. Can a driver decide not to give a breath test? And, what happens if a driver does not give a breath test? To answer these questions, we need to talk about Implied Consent laws.

Implied Consent laws require drivers arrested for DWI to give a breath sample. Above all, the Implied Consent laws require suspected drunk drivers to cooperate with BAC testing. If a driver does not provide a breath sample, DPS or the DMV will suspend his or her license.

The Texas Implied Consent law follows this pattern. It requires drivers arrested for DWI to give a breath test. Additionally, it requires police to give drivers over the age of 21 the following warnings:

  • If the driver does not provide a breath test, DPS will suspend his license for at least 180 days.
  • If the driver provides a breath test over the limit, then DPS will suspend his license for at least 90 days.
  • Police also tell the driver that if he or she refuses, police will get a warrant to draw blood.

Most important of all, these warnings show why drivers give breath tests. Drivers who cooperate get lighter suspensions. At the same time, these drivers make it easier for prosecutors to convict them on a DWI charge.

On the other hand, this is also why many drivers do not give police a breath test. Drivers suspected of DWI may reasonably decide it is a bad idea to provide a breath test. In this situation, police apply for a warrant.

DWI Blood Draws.

In blood-draw cases, a medical professional such as a nurse draws blood from a suspected drunk driver. The nurse injects a syringe needle into the driver’s vein and then draws the blood into a grey vial. After that, the nurse gently inverts or mixes the blood in the vial 8-10 times.

Notably, the blood vial contains two chemicals. These chemicals preserve the blood and keep it from clotting. This is why the nurse must properly mix or invert the blood vial. If the nurse does not mix the blood properly, then it could compromise the test results.

After that, the nurse places the blood vial into an evidence bag. And police send the vial to a lab for testing. Finally, the lab tests the blood for alcohol using a gas chromatograph with a headspace sampler.

The science for blood testing is technical. Nonetheless, the defense must make sure police properly collected the blood sample. This includes making sure the blood does not clot in the tube. And it includes checking for contamination.

For example, Candida albicans (CA) is a common yeast. It lives inside and outside the body. Strikingly, CA can combine with sugar to create alcohol. Thus, if CA contaminates a blood sample, it can create alcohol in the tube. This will cause a BAC level that is falsely high.

One important note on CA. The blood vials in DWI cases contain sodium fluoride (NaF). The scientific literature states that sodium fluoride prevents CA from creating alcohol in blood vials. But sometimes the vials are defective. Or, the nurse does not properly mix the blood with the sodium fluoride in the vial after the blood draw. At any rate, these are known issues. And the defense must explore them before trial.

DWI Breath Alcohol Testing.

Texas uses the Intoxilyzer 9000 for breath testing. It requires the driver to blow into a tube. The machine then takes this sample and looks for alcohol molecules. To do this, the machine uses infrared technology.

Hand drawing of Ethanol Molecule. San Antonio DWI Defense.
The DWI and DUI Intoxilyzer measures the infrared energy from the ethanol molecule. Further, this measurement will establish the blood alcohol concentration of the driver sometime after he is arrested. This is strong evidence that helps the prosecutors convict suspected DWI drivers.

Specifically, alcohol contains three atoms. Hydrogen, oxygen, and carbon. Chemical bonds link these atoms together. More importantly, these bonds absorb infrared light in a unique pattern. In essence, this pattern becomes a fingerprint. This allows the machine to find the alcohol and then measure it. Once the machine completes the test, it then prints out the results. These results contain the driver’s BAC level.

Breath Alcohol Testing vs. Blood Draws

Breath alcohol testing and blood draws do the same thing. They both attempt to measure the BAC of drivers arrested for DWI. But they differ in several important ways. In particular, the biggest difference is that blood draws are more invasive than breath tests.

Primarily, blood draws require a medical professional to put a needle in the driver’s vein. And blood draws gather more information than breath tests. As an example, a blood draw can show if the driver used cocaine, reefer, heroin, or methamphetamine. In contrast, breath tests require the driver to blow into a machine. This test captures a breath sample that does not contain the same amount of information as a blood sample.

For these reasons, the Supreme Court treats these two tests differently. Chiefly, police do not need a warrant to get a breath test. Conversely, it is not always clear when police need a warrant for a blood draw. But the Supreme Court provided guideposts to help on this issue.

DWI Blood Draws and the Fourth Amendment.

In a normal DWI case that does not involve an accident, police must get a warrant to draw blood. But if the DWI arrest involves a car accident, then police do not need a warrant. Similarly, police probably do not need a warrant if the driver is unconscious.

On the surface, these cases seem to conflict. They do not appear to make sense. The reason is the Fourth Amendment. Or more precisely, an exception to the Fourth Amendment. The Supreme Court calls this exception exigent circumstances. It means if there is an emergency, then police do not need a warrant for the blood draw. Otherwise, they must get a warrant for the blood draw.

But what happens if the test shows the driver is over the limit? Does this mean the driver is instantly guilty of DWI? And what if the driver disagrees with the test results? What are his or her options? Let’s turn to this topic now.

I am over the limit. Does this mean I am automatically guilty of DWI?

No. Breath and blood tests are powerful evidence. However, a BAC-test result, by itself, does not prove the driver was drunk at the time of driving. To convict a driver of DWI with a BAC test that is over the limit, the prosecutor must show:

  1. The BAC test provides trustworthy proof of alcohol in the driver’s breath or blood; and
  2. The driver’s BAC at the time of driving was over the limit based on the test.

If the prosecutors cannot show these two points at trial, then the driver is not guilty of DWI. See Kirsch v. State, 306 S.W.3d 738, 745 (Tex. Crim. App. 2010).

Next, let’s see how we can use this information to present a defense to a DWI charge.

Alcohol consumption follows a known pattern. First, the driver absorbs alcohol into the body. This happens when the driver drinks a beer, takes a shot of whatever, or sips a glass of wine. Second, the alcohol is distributed into the body. Finally, the body eliminates the alcohol. As the diagram below shows, these three phases create the BAC curve.

Texas DUI and DWI Blood Alcohol Concentration Graph.
The BAC graph shows the three phases of alcohol distribution. This includes the absorption phase, the peak phase, and the elimination phase. These phases help determine the blood alcohol concentration of a suspected drunk driver at the time of driving.

Moreover, the three cars in the diagram show a driver maybe anywhere along the BAC curve when he is pulled over. This can affect the accuracy of the BAC test that is taken at the police station. If the time gap between the stop and the breath test is significant, then the BAC test may not accurately represent the driver’s BAC at the time of the stop and arrest.

Furthermore, the driver’s body absorbs alcohol almost immediately after drinking. This is because alcohol mixes easily with water. The alcohol passes from the mouth to the stomach and intestines. From there, it goes into the blood and reaches the brain. At this point, the driver will start showing signs of intoxication. But the onset of intoxication depends on several factors.

BAC Absorption Factors

The rate of absorption varies from driver to driver. And it depends on many factors, including:

  1. Food in the stomach;
  2. Type of food in the stomach;
  3. Gender;
  4. Weight;
  5. Age;
  6. Mental state;
  7. Drinking pattern;
  8. Type of alcohol (beer, whiskey, or wine);
  9. Amount consumed; and
  10. Time period of drinking.

In short, these factors can distort the BAC curve. As a consequence, the BAC curve may not be as smooth as our diagram. And this distortion can lead to a falsely elevated BAC test result.

BAC Elimination Rate Factors

The absorption phase continues until the person stops drinking. Then, at some point, the BAC curve reaches its peak. From there, the BAC curve will begin to fall as the body eliminates the alcohol.

The elimination rate is slow but consistent. Many government lab techs state the rate is .015 per hour. In other words, the body eliminates alcohol at .015 per hour. But many scientists disagree with this number. Their point is that elimination rates vary from person to person. This too can affect the BAC curve and the accuracy of the breath test.

For instance, if police test the driver during the absorption phase, then his BAC at the time of the test may be higher than at the time of driving. This could lead to a wrongful conviction. Lawyers call this the rising-alcohol defense.

On the other hand, if police test the driver during the elimination phase, then his BAC at the time of the test may be lower than at the time of driving. And it is difficult to tell from a single breath test if the driver is in the absorption or elimination phase at the time of the test.

Finally, these examples show why DWI videos are important. A driver may be slightly over the limit. But if he or she looks good on the video and presents well, then a jury may give him or her the benefit of the doubt.

The larger the time gap between the DWI arrest and the test, then the more likely the test does not accurately measure the driver’s BAC at the time of driving. This is a critical issue in DWI cases. The law makes it a crime for the driver to be drunk when he was driving, not when he was tested. This can be a strong defense in close cases. For example, when the driver’s BAC test is moderately over the limit at the time of testing. In these situations, the BAC test may not accurately measure the driver’s true alcohol level at the time of driving.

San Antonio DWI and DUI Defense.

Alcohol is fun. That is why people drink when they hang out with friends. Normally, this is not a problem. Unfortunately, the police DWI dragnet catches many drivers with alcohol in their systems. Some of these drivers are drunk. Others are not. For those drivers who are drunk, a plea-bargain deal is the way to go. But for drivers wrongfully arrested for DWI, they should fight their DWI charge. This is especially for people facing a first-time DWI charge that may carry a heavy fine. And therein lies the rub–it is not always clear if a driver is sober or intoxicated at the time of driving from a single BAC test.

San Antonio DWI Defense Attorney Genaro R. Cortez.

Questions about your DWI charge? Call 210-733-7575 today for a free case consult.