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DUI/DWI Stops/Searches

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"The right of the people to be secure in their persons, houses, papers, and effects, against unreasonable searches and seizures, shall not be violated, and no Warrants shall issue, but upon probable cause, supported by Oath or affirmation, and particularly describing the place to be searched, and the persons or things to be seized."

— The 4th Amendment to the United States Constitution

In order to convict someone of driving while intoxicated (DWI) or driving under the influence (DWI), a defendant's Blood Alcohol Level (BAC) must have exceeded the legal limit of .08, or the prosecution must have other evidence that proves beyond a reasonable doubt that a driver was impaired or intoxicated. During stops and searches, evidence lawfully collected by the police may be used to support an arrest as well as by the prosecution to get a conviction. However, if the stop or search violated a defendant's rights under the Constitution or state statute, the evidence may be suppressed and the case may even be dismissed. If you have been charged with DUI/DWI, contact an experienced DUI lawyer to make sure your rights are protected.


Sobriety checkpoints (also known as roadblocks), traffic stops and traffic accidents are usually the starting point for police to gather evidence in support of a DWI/DUI charge. During the stop, an officer may observe the driver's behavior, ask questions and conduct field sobriety tests.

Traffic Stop. A police officer can lawfully stop a motorist based on a reasonable suspicion that a crime has been or is about to be committed. Erratic driving, broken tail lights and outstanding warrants may constitute reasonable suspicion. Swerving within your lane or anonymous tips without independent observations by the police probably won't provide the officer with a lawful basis for a traffic stop. If you wish to learn more about unlawful traffic stops in your jurisdiction, speak with a local DWI/DUI attorney.

Sobriety Checkpoints. The U.S. Supreme Court has ruled that sobriety checkpoints do not constitute an unlawful search and seizure if they meet certain requirements. Some states have additional rules on top of the federal requirements, and a handful of states, including Texas, prohibit sobriety checkpoints altogether.

Some of the requirements for roadblocks may include:

  • Advance notice of the checkpoint to the public
  • Police study showing why a checkpoint location is selected
  • A court order before the checkpoint is conducted
  • Certification to conduct field stops
  • The location of the roadblock must be safe and reasonable and not intended to target a specific population.


If the checkpoint violates state or federal law, the stop and subsequent arrest may be unlawful and the charges may be dismissed. Considering the potential cost of a DUI and the associated long term penalties, it is important to be aware of your rights in such circumstances. To learn more about the roadblock laws in your state, speak to a lawyer in your area. For a state by state analysis of sobriety checkpoint laws, visit the website of the Insurance Institute for Highway Safety.

Field Sobriety Tests. If you have been stopped for suspicion of DWI/DUI, the police may ask you to step out of the car and conduct field sobriety tests to determine if you are impaired or intoxicated. You do not have to consent to the testing; however, in some states failure to consent can result in an automatic suspension of your license and/or can be used as evidence against you. If you do consent, any number of physical and psychological tests may be performed, most commonly:

  • Horizontal Gaze Nystagmus or Eye Test – According to the National Highway Transportation Safety Administration (NHTSA), there are three indicators of impairment with this test: if the eye cannot follow a moving object smoothly, if jerking is distinct when the eye is at maximum deviation, and if the angle of onset of jerking is within 45 degrees of center.
  • Walk-and-turn – The purpose of this test is to see if the driver listens to and understands the instructions given by the officer and to see if the driver can walk a straight line.
  • One-leg-stand – The purpose of this test is to see if the driver can maintain balance.

Administration of the tests and interpretation of test results can be highly subjective. Factors that have nothing to do with the consumption of alcohol or any controlled substance — including medical conditions, anxiety, and language barriers — can cause a person to appear impaired. Fortunately, there is usually a video camera in the police dashboard recording the field sobriety tests, and your attorney can use it as evidence in your defense.

DWI/DUI Searches

24 Cues for Visual Detection of DUI Motorist

The National Highway Transportation Safety Administration (NHTSA) has developed a list of 24 cues that have been found to predict BACs of 0.08 percent or greater. The driving behaviors are subdivided into the following four categories:

  1. Problems maintaining proper lane position, including weaving, drifting, swerving or making wide turns
  2. Speed and braking problems, such as making jerky or abrupt stops, driving under 10 miles per hour or accelerating and decelerating rapidly for no apparent reason
  3. Vigilance problems such as driving into oncoming traffic, driving inconsistently with signaling and forgetting to turn on headlights
  4. Judgment problems such as driving off the road, driving with your head very close to the windshield and turning illegally

The more cues the driver exhibits, the greater the probability that he is impaired or intoxicated.

Source: National Highway Traffic Safety Administration

If the officer believes there is probable cause for a DWI/DUI arrest (meaning there are enough facts to support a reasonable belief that a driver is impaired by alcohol or has an unlawful amount of alcohol in his system or is impaired by drugs), your car may be searched and you will be asked to consent to breath, blood or urine testing.

Breath Tests. Breath tests measure alcohol content from a specimen of exhaled breath and are usually used to determine BAC. In some states, a preliminary breath test may be performed roadside with a portable machine, but these tests are not considered very reliable. Jurisdictions which permit portable BAC testing usually restrict the admissibility of the results, namely for an officer to establish probable cause for arrest. However, once a suspect is under arrest he or she usually takes a breath test at the police station on a more stable device such as a Breathalyzer, Datamaster, or Intoxilizer. Still, these results are routinely challenged for any number of reasons, including human error (such as improperly calibrating the machine for the correct height and weight), device error, and external factors (such as pre-existing medical conditions).

Blood & Urine Tests. A blood test measures the amount of alcohol in a person's blood and is usually considered a more accurate testing procedure than breath or urine testing (urine tests are used primarily when there is a suspicion of drugs — see sidebar). A DWI/DUI defense attorney knows the administration of these tests might be vulnerable to scrutiny if:

  • The blood was not drawn by a nurse, doctor, phlebotomist or other qualified person
  • The samples were not properly labeled or the wrong sample was analyzed
  • The samples were not properly refrigerated and stored
  • There was a break in the chain of custody

Each state has its own rules with respect to the manner, type and number of tests performed. In most states, refusal to consent to testing is automatic grounds for license suspension. Moreover, the defendant will likely face harsher DWI/DUI charges, which means increased license suspension periods, fines, penalties, and other more serious consequences if you are convicted.

Drug Impaired Driving

Generally speaking, drugs are more difficult to detect than alcohol. There is no standard equivalent to the test used to detect blood alcohol content. Most states do have a Drug Evaluation Classification program to train law enforcement officers to become certified Drug Recognition Experts for purposes of both recognizing drug impaired drivers and for presenting evidence in court. However, only 18 states have a "per se" law prohibiting a driver from having prohibited substances or drugs in the body while in control of a vehicle. Without a "per se" law, it is more difficult to get a conviction for drug-impaired driving.

Source: Governor's Highway Safety Association

DUI/DWI Lawyers

If you have been charged with DWI or DUI it is important to speak with an attorney as soon as possible. An attorney can help determine if the police conducted an unlawful stop or search or improperly administered and interpreted test results, and consider other defense strategies that could reduce the possibility of jail time for DUI, fines, license suspensions and other legal consequences for DUI that may not be appropriate in your case.