What the Prosecution Has to Prove in a DUI Case

An explanation of the elements that the prosecution must prove to get a DUI conviction when a case goes to trial.

By , Attorney · University of San Francisco School of Law
Updated by Jeff Burtka, Attorney · George Mason University Law School

Most driving under the influence (DUI) cases resolve through plea negotiations. But sometimes people charged with DUI decide to go to trial. At trial, the prosecution has to present enough evidence to prove the DUI beyond a reasonable doubt.

This article gives an overview of what the prosecution typically needs to prove to get a DUI conviction. For more detailed information about the DUI laws in your state, see our state-specific pages.

Elements of a DUI Charge

Generally, the prosecution needs to prove two elements for a jury to find a driver guilty of a DUI charge. The prosecution must show that the driver was:

  • driving, operating, or in physical control of a vehicle, and
  • under the influence of alcohol or drugs.

Some states also require the prosecution to prove a third element: The driver was driving on a public—rather than private—road.

If the prosecution can prove these elements beyond a reasonable doubt, chances are the jury or judge will convict the driver.

The "Driving" Element of a DUI

People often are surprised to learn that they can be convicted of a DUI despite never actually driving a vehicle. In many states, a person doesn't have to put a vehicle into motion to get a DUI.

Even though most of these states still call the crime "driving under the influence" (DUI) or "driving while intoxicated" (DWI), prosecutors can prove the "driving" element by showing the motorist was "operating" or "in actual physical control" of a vehicle. In other words, evidence that the driver was behind the wheel with the car in motion isn't always required to prove the driving element.

Some states, however, require proof of actual driving for a DUI conviction—merely being in control of the vehicle or having the car's engine on isn't enough. For example, in California, a defendant can be found guilty of a DUI only if the prosecution proves "volitional movement of a vehicle." In other words, the prosecution must show that the defendant willfully drove the car. Mercer v. Department of Motor Vehicles, 53 Cal.3d 753 (1993).

In states that don't require actual driving, laws vary on what exactly it means to be operating or in actual control of a vehicle. But the judge or jury deciding the case typically will look at a variety of factors when deciding whether the prosecution has proved the operation or control element. These factors can include whether:

  • the defendant was sleeping or awake
  • the defendant was in the driver's seat
  • the car keys were in the defendant's possession
  • the car's motor or electrical systems—radio, heat, air conditioning, or lights—were on, and
  • the car was parked in a way that posed a danger to other motorists.

For instance, if a defendant was asleep in the back seat with the engine off and no electrical components on, the prosecution likely couldn't prove operation or control in many states.

On the other hand, if a driver was intoxicated and in the driver's seat with nothing turned on, but with the keys in the ignition, the prosecution likely could prove a DUI in states that only require control. And a driver who was drunk and in the driver's seat with the engine on likely will be guilty of DUI in states that require either operation or control of a vehicle.

Again, states have different laws, so there isn't a one-size-fits-all answer to what "operation" or "control" means. In most cases, it's best not to risk a DUI conviction by getting into your vehicle when intoxicated—unless someone who's sober is in the driver's seat.

How Can the Prosecution Prove Someone Was Driving in a DUI Case?

The prosecution usually will prove the driving, operation, or physical control element by providing the testimony of police officers or other witnesses who saw the defendant in the vehicle. Video evidence from cell phones or police dashboard cameras is another common type of evidence that can help prove this element.

In states that require proof that the defendant was driving, video evidence or witness testimony placing the defendant behind the wheel of a moving vehicle isn't always required. The prosecution sometimes can rely on circumstantial evidence of driving, such as police officers testifying that they arrived at a crash scene and found the defendant alone in the driver's seat.

The "Under the Influence" Element of a DUI

To prove a driver was under the influence, the prosecution generally has two options:

  • proving a "per se" DUI—meaning the driver had a blood alcohol concentration (BAC) of .08% or more (.05% or more in Utah), or
  • showing that the motorist was actually impaired by drugs or alcohol.

Proving BAC is usually easier than showing impairment. But it's common for prosecutors to file two charges in a DUI complaint—one based on impairment and a second alleging excessive BAC.

By filing two charges, the prosecution can maximize the chances of getting a conviction. For instance, if something was wrong with the BAC test, the prosecution can still prove the case with other evidence of impairment.

What Kind of Evidence Can the Prosecution Use to Prove BAC?

The prosecution will prove BAC through the results of chemical test of blood, breath, or urine. At trial, the prosecutor will ask the judge to admit a certificate from the test showing that the driver's BAC was above the legal limit.

Even though a per se DUI is often easy to prove, the prosecution has to show that the chemical test was properly conducted. The prosecutor will need the person who administered the chemical test to testify. If there was any machine or human error, a judge potentially could throw out the results of the test.

Challenging the results of a chemical test can be complicated. For more information, read about per se DUIs.

What Kind of Evidence Can the Prosecution Use to Prove Impairment?

To prove impairment, the prosecution needs evidence that the defendant was under the influence of drugs or alcohol at the time of driving. In addition to BAC results, typical evidence that a prosecutor could use includes:

  • results of field sobriety tests
  • a drug influence evaluation by a drug recognition expert
  • videos or witness descriptions of the defendant's poor driving
  • the defendant's statements to police or other witnesses about drinking alcohol or using drugs
  • blood test results showing drugs in the defendant's blood
  • testimony from a toxicologist (a scientist who studies chemicals and other substances) about the effects of specific drugs, and
  • police statements about the defendant's appearance—like red and watery eyes, the smell of alcohol, slurred speech, and stumbling.

The prosecutor usually will need more than one of these types of evidence to show a defendant was impaired. For instance, a driver could claim a distraction or sleepiness caused poor driving. But if the driver also admitted taking drugs and was seen stumbling around and acting erratically after stepping out of the vehicle, the prosecution will have a much stronger case—and the defendant will have a harder time explaining the poor driving.

The "Public Roadway" Element of a DUI

Some state laws prohibit driving under the influence anywhere in the state. In these states, you can get a DUI regardless of whether you were driving on a public road or private property.

In other states, however, drunk or drugged driving is illegal only in places that are "open to the general public." Places open to the public include not only public properties like city streets and state highways but also privately owned properties like shopping mall parking lots.

Talk to a DUI Attorney

The consequences of a DUI conviction are serious, and DUI laws vary by state. If you've been arrested for driving under the influence, get in contact with an experienced DUI lawyer in your area. A good DUI attorney can analyze the facts of your case and tell you how the law of your state applies.

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