In deciding which defenses could apply in your driving while intoxicated (DWI) case, your lawyer will look at all the evidence produced by the police and interview witnesses. Some common defenses seen in DWI cases include:

Driving Observation Defenses

The prosecutor always relies (sometimes exclusively) on the arresting police officer's testimony about how a DWI suspect was driving, including:

  • Very slow speeds
  • Uneven speeds (very fast, then very slow, for example)
  • Weaving from one side of a lane to the other
  • Crossing the center line of the highway
  • Running a red light
  • Hesitation in going through a green light

A good defense attorney will argue that there are many different explanations for these driving behaviors that don't have anything to do with being alcohol-impaired.

Behavior Observation Defenses

An officer may also testify as to a DWI suspect's appearance and behavior when questioned, including:

  • Slurred speech
  • Bloodshot eyes
  • Inappropriate joking or incoherent speech
  • Stumbling or not being able to walk very far
  • Pupil enlargement

Defenses to these observations that don't have anything to do with being intoxicated may include:

  • Lack of sleep
  • Allergies
  • Contact lenses
  • Stress due to personal circumstances
  • Medications
  • Foods recently ingested
  • Nervousness over being stopped by police
  • Physical impairments

Field Sobriety Test Defenses

When an officer suspects you may be too intoxicated to drive, he or she will likely ask you to perform what are called "field sobriety tests." These tests are designed to assess your physical and mental alertness, and can include:

  • Walking a straight line
  • Walking backwards
  • Reciting the alphabet, frontwards or backwards
  • Standing on one leg

Officers also sometimes rely on what's called a "nystagmus" test, in which the suspect is asked to shift eye gaze from one side to the other while the officer shines a light in his or her eyes. The theory is that the gaze of someone who is impaired by alcohol or drugs will be jerky rather than smooth.

The defenses to field sobriety tests are often the same as with officer observations. Medications and lack of sleep can make it considerably more difficult to perform these tests. Many people also have physical impairments caused by injuries - or simply aging -that make it impossible to perform these tasks under ideal conditions.

Your lawyer may cross-examine the arresting officer in detail as to whether the officer asked you if you had physical impairments or there were particular circumstances that would make it difficult to perform the tests. Your lawyer may also point out to the jury that many jury members may have similar difficulties performing the tests, such as by asking the jury if they could recite the alphabet backwards under the best of circumstances.

Blood Alcohol Content Defenses

When you consume alcoholic drinks, the alcohol is absorbed into your blood stream. The level of alcohol in your blood, called the Blood Alcohol Content ("BAC") can be measured by different tests. In all states, you're presumed to be drunk and unable to safely operate a vehicle if your BAC is .08 or greater. This measurement means that your blood contains eight/ one-hundredths percent of alcohol.

All states have lowered the BAC level defining intoxication to .08, and have "zero tolerance" laws that make it illegal for people under 21 to operate a vehicle with little or no amount of alcohol in their blood.

Many states also have more severe DWI or DUI penalties for driving with a high BAC, which is often defined as a level measuring more than .15 to .20.

Your BAC can be determined from a blood draw, which is often automatically taken if you are involved in an accident and there is a suspicion that you may have been drinking. Your blood will also be drawn if you are taken to the hospital because the police are concerned that you may have had so much to drink that you are in danger of alcohol poisoning and should be hospitalized for observation and/or treatment.

Most DWI suspects have their blood tested by blowing into a breath testing device. These devices can be faulty and not well-maintained or properly calibrated. They can register false results based on your consumption of food and other non-harmful substances other than alcohol or drugs.

Your attorney will likely subpoena police records on how the breath testing machine operates and was maintained and calibrated. Your lawyer may also want to bring in expert testimony that the particular breath testing machine the officer used is notorious for malfunctioning.

Depending on the jurisdiction, another defense to breath testing machines arises when the physical breath tests aren't preserved as evidence, allowing for independent testing later. Your attorney can argue that there's no way to know if the machine that was used was accurate, if your breath samples can't be independently tested.

Many of the defenses against DWI charges require a lawyer's expertise and experience. If you've been charged with DWI, it's important to contact a lawyer right away.

Related Resources on Lawyers.com
- DUI DWI Defenses
- Driving While Intoxicated FAQ
- DUI/DWI articles and information
- Selecting a Good Criminal Lawyer
- Find a Criminal Lawyer in your area
- Visit our Criminal Law Message Board for more help

Web Resources
- Blood Alcohol Content (BAC) Calculator (University of Oklahoma)
- Blood Alcohol Content (BAC) Calculator (St Clair County Sheriff)

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