Many drunk driving cases in Virginia and around the country are resolved in the same way: Toxicology evidence is used to establish intoxication, and the defendant then pleads guilty in return for charging or sentencing concessions. However, there are situations where an individual accused of getting behind the wheel while impaired may choose to eschew plea offers and mount a defense.
Challenging toxicology evidence
The science supporting blood and breath tests is broadly accepted, and the equipment used to perform them is both sophisticated and accurate. However, this kind of evidence is often unreliable due to human error. A blood test might be excluded in a DUI case if prosecutors cannot provide a clear chain of custody for the sample that was tested, and a breath test result could have little value as evidence if the machine that measured the defendant’s blood alcohol concentration was defective or poorly maintained.
The fruit of the poisonous tree
Claiming that the police acted improperly is one of the most common drunk driving defenses. When police officers pull vehicles over for no reason, drunk driving charges that stem from the traffic stop may be dismissed even if the evidence of intoxication is strong. This is because the Fourth Amendment limits what the police can do and only permits traffic stops in certain situations. When a traffic stop violates the Fourth Amendment, any evidence discovered as a result is excluded under the “fruit of the poisonous tree” doctrine.
DUI suspects sometimes admit that they were drunk and mount affirmative defenses to explain their behavior. Two of the most common affirmative defenses in DUI cases are involuntary intoxication and necessity. A drunk driving defendant could mount an involuntary intoxication defense if they consumed food or drink that had been laced with an intoxicating substance. Alternatively, they may claim they acted out of necessity if they got behind the wheel while under the influence to rush a badly injured person to an emergency room.
Depending on the circumstances, a person arrested for DUI may choose to fight the charges. Drunk driving defenses are usually based on challenging the results of blood or breath tests, questioning the behavior of the arresting police officer or admitting that the defendant broke the law but claiming they had no choice.