An arrest for driving under the influence can feel like the walls are closing in. A blood test result and a night in a holding cell can leave a person convinced that a conviction is certain. In reality, a DUI charge is only an accusation. Prosecutors still carry the burden of proving every element of the offense beyond a reasonable doubt, and the evidence behind many DUI arrests is less solid than it may first appear.
A DUI defense attorney can review police reports, test results, and video footage to find weaknesses in the prosecution’s case. Depending on the facts, a skilled defense lawyer may be able to challenge evidence, negotiate reduced charges, or seek a dismissal.
When Can Drivers Be Charged With DUI?
DUI charges in most states rest on two separate theories, and prosecutors often file both at once. The first is the “per se” offense. In nearly every state, an adult driver with a blood alcohol concentration (BAC) of 0.08 percent or higher is legally considered intoxicated, regardless of how well that driver was actually handling the vehicle. Utah is a notable exception, with a lower limit of 0.05 percent.
Lower limits apply to certain drivers. Commercial drivers operating commercial vehicles generally face a 0.04 percent limit. Drivers under 21 are subject to “zero tolerance” laws in every state, which typically set the limit at 0.02 percent or lower.
The second theory is impairment. A driver may be charged with DUI even with a BAC below 0.08 percent if the officer believes alcohol affected the person’s ability to drive safely. Impairment charges also cover drugs, including illegal substances, prescription medications, and in many states, cannabis. Some states even allow charges against a person who was sitting in a parked car with the engine running, under laws addressing “actual physical control” of a vehicle.
What Is the Rising BAC Defense?
The rising BAC defense focuses on the gap in time between driving and chemical testing. Alcohol does not enter the bloodstream all at once. Depending on factors like food intake, body weight, and the type of drink, the body can take 30 minutes to two hours or more to fully absorb alcohol after the last drink.
Breath and blood tests are rarely given at the roadside the moment a driver is pulled over. Often, an hour or more passes during the stop, the arrest, transport to a station, and the required observation period before testing. If a person had a drink shortly before driving, that person’s BAC may have still been climbing during that time.
As a result, a test reading of 0.09 percent taken at the station does not necessarily mean the driver was at 0.09 percent while behind the wheel. The driver’s BAC may have been below the legal limit while driving, and it may only have crossed the line later. This defense often relies on a timeline of when and what the person drank, receipts, witness statements, and testimony from a toxicology expert. Some states have passed laws that make this defense harder to raise, so its strength varies by jurisdiction.
Reasonable Suspicion Defenses in Drunk Driving Allegations
Police officers cannot pull a driver over without a valid legal reason. Under the Fourth Amendment, a traffic stop requires reasonable suspicion that the driver committed a traffic violation or was involved in criminal activity. A hunch or a general feeling is not enough. Common justifications include speeding, weaving across lanes, rolling through a stop sign, or a burned-out taillight.
If the stop itself was unlawful, the evidence gathered afterward may be thrown out. That can include the officer’s observations, field sobriety test results, and chemical test results. Without that evidence, the prosecution may have little left to work with.
Defense attorneys often compare the officer’s written report with dashcam or bodycam footage. Sometimes, the video may show that a driver stayed within their lane or came to a full stop, contradicting the stated reason for the traffic stop. Similar challenges can apply later in the encounter. An officer generally needs probable cause, a higher standard than reasonable suspicion, to make an arrest. Sobriety checkpoints also have to follow specific rules, and a checkpoint that did not meet those standards can be challenged as well.
Chain of Custody Issues Can Affect DUI Cases
Blood and urine samples taken in DUI cases must be handled carefully from the moment they are collected until they are tested in a lab. The record of that handling is known as the chain of custody. It should show who drew the sample, who handled it, where it was stored, and how it was transported, with no unexplained gaps.
Mistakes in this process are more common than many people realize. A vial may be mislabeled or confused with another person’s sample. A sample may sit unrefrigerated, which can allow for fermentation and artificially raise the alcohol level. Vials missing the proper preservative or anticoagulant can produce unreliable results.
When the chain of custody is broken or poorly documented, the defense can question whether the test result actually reflects the defendant’s BAC. Breath test evidence raises related concerns. Breath testing machines must be properly calibrated and maintained, and the officers operating them typically must be certified. Missing maintenance logs or expired certifications can weaken the reliability of a breath test result.
False Positives in Field Sobriety Tests and Officer Observations
Field sobriety tests are often presented as strong evidence of impairment, but they are far from foolproof. The three standardized tests recognized by the National Highway Traffic Safety Administration are the horizontal gaze nystagmus (eye movement) test, the walk-and-turn test, and the one-leg stand test. Each of these tests can be affected by factors that have nothing to do with alcohol.
Officer observations are similarly open to challenge. Bloodshot eyes can come from allergies, fatigue, or contact lenses. Slurred speech may reflect a speech impediment, a strong accent, or simple nervousness. The smell of alcohol can show that a person had a drink, but it says nothing about how much that person drank or whether that person was impaired. When these observations are viewed alongside video footage and medical history, they often tell a very different story than the one in the police report.
Disclaimer: This article is for general informational purposes only and does not constitute legal advice. Reading it does not create an attorney-client relationship. Laws vary by state and change over time. Anyone facing a DUI charge should consult a licensed attorney in their jurisdiction.
