DWI Testing

You have probably seen DWI testing online or on television before. A person is pulled over by a police officer and is asked to participate in certain physical and chemical tests. They may be asked to recite the alphabet backwards or submit to a breathalyzer test.  No matter the circumstances, it’s important you thoroughly understand DWI testing so you’re prepared if an officer pulls you over.

Law enforcement use a variety of tests to measure your impairment level. An officer will probably first ask you to participate in field sobriety testing. These physical exercises are designed to determine if your physical and mental faculties are impaired. Police officers may also use chemical testing during a DWI stop, which is where they ask for a urine sample. breathalyzer test or a blood draw.

A failed DWI test can lead to an arrest. If you or someone you know has failed or submitted to DWI testing, it’s imperative you contact an experienced criminal defense attorney.

Attorney for DWI Testing in Houston, Texas

The consequences of a DWI can be stressful and costly. It’s likely the judge will impose certain conditions on your sentencing such as DWI classes or the installation of an ignition interlock device (IID). Additionally, a DWI conviction could lead to expensive fines and even prison.

You can choose to fight back today by hiring [firm]. Our criminal defense attorneys at [firm] have a special focus in DWI law. Our managing attorney Tyler Flood has been designated as an ACS-CHAL Lawyer-Scientist. This means he has an in-depth knowledge in the science behind chemical testing. Contact us now at [phone] to set up your consultation today.

[firm] accepts clients throughout the greater Harris County area including Bellaire, Tomball, West University Place and Houston.

Overview of DWI Testing in Texas

What Are Field Sobriety Tests?

Police officers tend to start with field sobriety tests when they pull someone over for DWI. These physical activities were created by law enforcement to identify signs of intoxication. You may have seen a variety of field sobriety tests on television, but only the three standardized by the National Highway Traffic Safety Administration (NHTSA) are admissible in court.

Listed below are the three field sobriety tests created by NHTSA.

  • Horizontal Gaze Nystagmus (HGN) – HGN tests are considered the most accurate out of the three tests. It’s designed to measure the involuntary jerking of the eye, which is a sign of inebriation. The officer will start the test by holding a “stimulus” such as pen about 11 to 13 inches away from your face. They will then move the object side to side and ask you to follow it with your eyes. If you’re unable to track the item with your eyes, then it’s considered a sign of intoxication.
  • One-Leg Stand (OLS) – Another common field sobriety test is the one-leg stand. A police officer will ask you to stand on one foot about six or so inches off the ground. You will then be instructed to count aloud for about 30 seconds. The officer will look for certain signs of inebriation such as excess swaying, hopping, or the inability to stay balanced.
  • Walk-and-Turn (WAT) – Police officers may ask you to participate in a walk-and-turn test. You will be asked to take nine heel-to-toe steps along a straight line. Once you reach the end of the line, the officer will ask you to turn on one foot to take another nine heel-to-toe steps back. Law enforcement may arrest you for DWI if you have issues staying on the line or staying balanced.

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Problems with Field Sobriety Testing

Field sobriety testing is still a developing field based on questionable science. It’s been proven that certain environmental or external factors could affect your results. The tests are also universal, so they don’t take into account factors such as disabilities, age or physical ability. Because of this, the majority of attorneys question the validity of field sobriety tests.

Listed below are factors that can cause a completely sober person to fail a field sobriety test.

  • Age;
  • Physical disabilities;
  • Improperly given instructions;
  • Fatigue;
  • Inclement weather;
  • Certain medical conditions;
  • The temperature outside;
  • Extreme anxiety and nerves;
  • Eye-to-hand coordination;
  • Slippery roads;
  • Some shoes such as flip flops;
  • Terrible balance;
  • Prior injuries or surgeries;
  • Certain prescription or over-the-counter drugs; and
  • Physical ability

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Chemical Testing for DWI

Law enforcement may ask you to participate in field sobriety tests, but the most valuable evidence comes from chemical testing. Officers use three different types of chemical tests to measure your blood-alcohol concentration (BAC). If you have a BAC of .08 or higher, then you’ll legally be considered intoxicated and charged with DWI.

The following are the three types of chemical tests utilized by law enforcement.

  • Breath Analysis (Breathalyzers) – Most people think of breath analysis when they hear DWI chemical testing. Officers will typically use a breathalyzer, which can be portable or full-sized at their local station. The device measures the number of grams of alcohol per 210 liters of breath and can give skewed results if it isn’t maintained properly.
  • Urine Analysis – You might be asked to give a urine sample if officers suspect you’re under the influence of drugs. The test measures the number of grams of alcohol per 67 milliliters of urine. The results of your test will be determined by qualified lab personnel.
  • Blood Analysis – Police may ask you to submit to a blood draw after a DWI stop. This type of chemical testing is considered to be the most accurate of the three. The test is to measure the number of grams of alcohol per 100 milliliters of blood. It’s rare for law enforcement to ask for a blood sample, but they might if they believe you’re driving under the influence of a controlled substance.

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Common Errors with Chemical DWI Testing

The chemical tests administered by law enforcement are by no means flawless. Many sober people have failed chemical testing because of outside factors. Additionally, badly maintained equipment or mishandled samples could also lead to inaccurate results. A skewed test result could be pivotal evidence for the prosecution, meaning it could devastate your case.

Listed below are some common issues with DWI chemical testing.

  • Diluted samples;
  • Contaminated samples;
  • Mishandled samples;
  • Poorly maintained equipment;
  • Old outdated equipment;
  • Unsupervised test administrators;
  • Unqualified personnel;
  • Improper procedures;
  • Results were determined by an unqualified laboratory; and
  • Tampered test results

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Can I Refuse DWI Testing in Texas?

It’s overwhelming when you’re pulled over for DWI. However, it’s important to understand you have choices. You’re not obligated to undergo field sobriety or chemical testing simply because an officer asked you to. They may even threaten you with jail or a suspended license, but what they won’t tell you is that will happen anyway if you fail DWI testing.

It’s important you understand there are some consequences to refusing chemical tests. Refusing blood, urine or breath analysis tests is a violation of implied consent laws. These laws state that you are implicitly agreeing to chemical testing if you drive on Texas public roads. This means you could have your license suspended for a period of time if you refuse chemical testing. If the officer has probable cause you’re intoxicated, then you could also be arrested.

No one wants to be arrested or have their license suspended. However, both of those are much easier to handle than a DWI conviction. You’ll only be in jail for a short period of time and the prosecution will have no concrete evidence against you. Without that valuable scientific evidence, it will be hard for them to win your case.

You can also contest your license suspension with an administrative license revocation (ALR) hearing. At the hearing you can employ legal representation to fight your license suspension. It’s important you act quickly though. You only have 15 days after arrest to file a request for an administrative license revocation hearing.

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Additional Resources

Instructor Guide to DWI Testing – Visit the official website of the National Highway Traffic and Safety Administration (NHTSA) to access their instructor guide for DWI detection. Learn more about standardized field sobriety tests, NHTSA data and signs officers look for.

Administrative License Revocation (ALR) Hearing – Visit the official website of the Texas Department of Public Safety (DPS) to learn more about their administrative license revocation (ALR) program. Access the site to read more about the consequences of refusing to submit to testing, the suspension terms from refusing and more.

DWI Defense Lawyer in Harris County, Texas

If you or someone you know has been charged with DWI, it’s imperative you seek legal representation. You could have undergone a faulty field sobriety or chemical test during your stop. If you refused testing, then you will need to contest your suspended license with an administrative license revocation hearing.

Contact [firm] to discuss your charges. [firm] will assess your case to find the best legal avenue to take. Call [phone] now to set up a free consultation. Our attorneys practice law throughout the Houston metropolitan area including Uptown, Greenspoint and River Oaks.

This article was last updated on March 13th, 2019.


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Robert Henderson
Robert Henderson
December 22, 2023.
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Zeta Ze
Zeta Ze
December 15, 2023.
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briana Munoz
briana Munoz
December 5, 2023.
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October 19, 2023.
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October 12, 2023.
Houston DWI/DUI Attorney Tyler Flood is the best in the business! Tyler and his team made the entire process stress free for what is a very stressful situation. From winning the first administrative hearing (to retain my license/avoid a breathalyzer) to getting the dismissal before trial even started. He is truly the best in the business!
Cesar Ricardez
Cesar Ricardez
October 3, 2023.
I hired Tyler Flood the day after my DUI arrest after reading glowing reviews about him and I couldn’t be happier that I did so. He took care of both my cases to keep my driving rights and the misdemeanor DUI charge in court. I never even had to appear in court or do anything, him and his team took care of anything while I carried on with my life and would just get updates whenever they appeared in court on my behalf. At the end, my driver license was never suspended and they got my case dismissed. Lesson learned, I don’t wish anyone to get in my situation but if you do, don’t hesitate to hire Tyler Flood and his team, they are extremely professional and they go for the win. No deal, no probation, got it all dismissed.
September 14, 2023.
Tyler Flood, Houston DWI/DUI attorney is fantastic! He is professional, smart and takes pride in getting the best possible outcome for you. This was my second DWI and I didn't want to take chances. I found him on Google and I too was in disbelief with all the 5.0 star reviews. Upon meeting him I quickly discovered it was all true. A lawyer with his own science lab WTH??????? Long story short he got my case dismissed without going to court. You can not put a price on freedom. The only downside is I only hope to need his services this one time. 😀 Thanks again Mr. Flood God bless.
John Sellers
John Sellers
August 31, 2023.
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August 29, 2023.
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Trey Perrett
Trey Perrett
August 14, 2023.
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