Every state has laws prohibiting impaired driving. The main purpose of these laws is straightforward—to protect the public by discouraging motorists from drinking and driving.
However, the technical aspects of how DUI laws define the offense sometimes provide opportunities to fight and beat DUI charges. Defense attorneys might also be able to defeat a DUI charge by attacking the reliability of chemical tests (alcohol and drug tests) or pointing out that police didn't adhere to procedural requirements or violated the driver's constitutional protections.
This article goes over some of the common DUI defenses and how DUI lawyers use them to win cases.
The "elements" of a DUI charge are the parts that the prosecution must prove to get a conviction. The two elements of a DUI charge are:
If the prosecution isn't able to prove both of these elements beyond a reasonable doubt, the driver will beat the charge. So the main goal of a DUI defense is to prevent the prosecutor from establishing at least one of these two elements in court
The DUI laws of each state are a little different, and the facts of every case are unique. So a defense that might work in one case might not work in another. But the DUI defenses that tend to work best usually fall into one of the following categories:
These are big topics, so we'll break them down a bit more.
Before a DUI investigation even begins, the officer must have a valid reason for pulling over a driver. In other words, the officers must have an articulable and reasonable suspicion that the driver has committed some crime (a DUI checkpoint is one notable exception to this rule). Otherwise, the traffic stop is generally illegal.
The 4th Amendment to the U.S. Constitution protects persons from unlawful searches and seizures. A traffic stop is considered a seizure. So an illegal stop violates the 4th Amendment. What this all means is that any evidence of criminal activity found during or following an illegal stop (such as the officer's observations or alcohol test results) can't be used against the driver in court.
When a driver is able to get evidence thrown out in this way (establishing the traffic stop was illegal), the prosecution isn't left with much and will normally dismiss the charges.
DUI defenses that focus on the "driving" element will look different depending on the laws of the state.
In a few states—including California—the prosecution must prove the motorist was actually driving to get a DUI conviction. In these states, a driver might be able to beat a DUI charge if there's no witness who saw the vehicle in motion with the driver at the wheel. After all, the prosecution must prove the charges beyond a reasonable doubt. It's pretty hard to prove driving when no one actually witnessed it.
In the vast majority of states, the prosecution just needs to prove the driving was operating or in "actual physical control" of a vehicle to get a DUI conviction. Basically, actual physical control means the driver (although not yet driving) was in a position where he or should could, without much effort, put the vehicle in motion.
As you might imagine, in states that have actual physical control laws, it's sometimes more difficult for drivers to use a driving-element defense. However, if the circumstances show that it would have taken significant time or effort for the driver to put the car in gear, a driving-element defense could still work. Factors that could make this type of defense more viable might include things like:
The laws of each state and the facts of each case are different. But, generally, the judge or jury deciding the case will be looking at how easy it would have been for the impaired motorist to start the car up and drive off.
Most DUI defenses focus on the impairment element. The goal of an impairment defense is generally to:
If the defense is able to succeed on any of these strategies it can mean beating a DUI charge in court.
In most DUI cases, the prosecution relies heavily on blood or breath test results to prove the charges. Generally, implied consent laws require drivers who are lawfully arrested for a DUI to agree to take one of these tests. Drivers who refuse will normally face license suspension and possibly other consequences.
However, blood and breath tests are also considered to be searches and seizures under the 4th Amendment and similar rules contained in state constitutions. So, despite what implied consent laws say, if an officer violates a driver's constitutional rights in the process of obtaining a blood or breath sample, the results won't be admissible in court.
Under the federal constitution (which applies to all states), police generally must have a warrant to conduct a blood draw. The constitutions of many states also require warrants for breath tests. There are exceptions to the normal warrant requirement; however, in cases where police don't obtain a warrant, there at least could be a defense to the charges based on the lack of a warrant. But because this is a complex issue, it's best to talk to an attorney if you think your case might involve an illegal warrantless breath test or blood draw.
Because blood and breath test results are often crucial for prosecutors trying to prove a DUI case, many defenses center around discrediting the reliability of these tests.
Chemical tests are conducted using various equipment and incorporate scientific calculations to produce results. So prosecutors generally must prove the procedures and equipment used for testing were reliable. For example, a court might not accept breath test results if the machine wasn't properly calibrated or the officer didn't follow best practice for ensuring the sample wasn't tainted. Or a judge might be reluctant to admit blood test results into evidence if the prosecution can't prove the sample was handled and stored properly.
Even where the judge allows chemical test results into evidence, the defense might still be able to cast doubt on their reliability at trial. If jurors become convinced that the results are shaky, there's a good chance they'll be unwilling to convict.
If chemical test results are unavailable, the prosecutor will have to prove actual impairment—that the driver was unsafe to operate a vehicle.
Prosecutors often attempt to prove impairment by having the arresting officer testify in court. Officers normally testify as to their observations such as poor field sobriety test performance, slurred speech, and the odor of alcohol on the driver.
A good defense lawyer might be able to discredit the observations of the officer in various ways. For example, a defense attorney might provide an innocuous explanation (such as a physical handicap or nervousness) for why the driver didn't do well on field sobriety tests. It's also possible for mental illness to be mistaken for drug impairment. So providing evidence to the jury that the driver suffered from some type of mental or emotional issue could work in the defense's favor.
After consuming alcohol, a person's blood alcohol concentration (BAC) is in a constant state of change. As the alcohol absorbs into the body, the person's BAC rises. At some point, the person's BAC will peak and then begin to decline as the body metabolizes the alcohol.
When there's a long delay between when a motorist was driving and when the blood alcohol test occurs, it's sometimes possible to use the rising-blood-alcohol defense. With this defense, the driver is basically arguing that, although the BAC was above the legal limit when the testing occurred, the BAC was in the process of rising and was below the legal limit at the time of operation. This defense tends to work best when the driver's BAC was just barely about the limit.
With most defenses, the idea is to prevent the prosecution from proving the elements of the offense. Put differently, the focus is on what the prosecution can't prove rather than what the driver can prove.
However, in some states, there are also "affirmative defenses" to DUI charges. With an affirmative defense, the driver has the burden of proof. In other words, the driver must present evidence in court that establishes the defense.
For DUI cases, one of the most common affirmative defenses involves situations where the driver's impairment resulted from taking a prescription medication. With this defense, it's up to the driver to prove that he or she was taking medication as prescribed.