Driving While Impaired Trial Defenses

Constitutional Defenses

The Constitution and state statutes provide a number of powerful defenses to a Driving While Impaired Charge.  These defenses are normally raised in hearings that occur before the trial and require the defense lawyer to file a motion in limine requesting relief.

Two of the most important defenses invoke an individual's Fourth Amendment rights:

The right of the people to be secure in their persons, houses, papers, and effects, against unreasonable searches and seizures, shall not be violated, and no Warrants shall issue, but upon probable cause, supported by Oath or affirmation, and particularly describing the place to be searched, and the persons or things to be seized.

The first challenge implicates the reason for the stop of a car. In a typical DWI case, the driver is stopped by a police officer as he is driving along a road.  That stop must be based on specific, articulable facts that justify the stop.  In other words, the officer must be able to explain the specific facts he observed that caused him to stop the car.

If the officer fails to adequately explain the reason for the stop, or stopped the car on a mere hunch, a suppression motion will result in the suppression of evidence collected by the officer during and following the stop.  In short, the case will be dismissed.

The second challenge asserts that the officer lacked sufficient evidence to arrest the person. The officer typically conducts a brief investigation to determine whether alcohol or drugs might be present in the person's system.  This investigation may include the use of preliminary breath tests (PBT) or various standardized field sobriety tests (SFST).  In addition, the officer will typically take note of any odors, red eyes, slurred speech, and statements by the driver admitting to have previously drunk alcohol.

If the officer fails to collect sufficient details to support a charge of Driving While Impaired, the officer lacked probable cause.  Probable cause is evidence gathered that suggests to a reasonable person that the person was probably engaged in the criminal act.  A failure to establish probable cause prior to arrest will lead to the dismissal of a DWI charge.

Checkpoint Stops

Road block cases present their own special set of challenges for the state.  The Supreme Court of the United States has held that police can establish checkpoints, but only for specific programmatic purposes.  General law enforcement road blocks are frowned upon in the United States.

Checkpoint cases require that the state produce a legally valid plan that establishes the manner, method, and deviations permitted during the road block.  And the state must show the court that the officers conducting the checkpoint followed the plan throughout the checkpoint.  Any deviations are only permitted insofar as they are outlined in the plan.

Finally, the officers working at the checkpoint on a particular night must be assigned to that location by a cooperation agreement between their respective agencies.  Officers from one police department may not simply show up and help another department's officers.

Failure to abide by these legal and constitutional requirements can result in the DWI being thrown out of court, and in certain cases can result in the dismissal of all similarly situated DWI cases resulting from a poorly run checkpoint.

Pre-Trial Statutory Defenses

Under North Carolina law, a person has the right to have a witness present during the chemical analysis conducted at the detention facility.  In short, the defendant may call a friend or attorney to come watch him blow into the breathalyzer machine.

The failure to permit the defendant to call a friend, or to permit that person to come into the breathalyzer room to observe the blow can result in relief. The North Carolina Court of Appeals in State v. Ferguson and its progeny has held that such a rights violation can result in either a suppression of the breath result or rise to the level of a constitutional violation that can result in a dismissal of the charges.North Carolina bail statutes require that a person be released on the least restrictive conditions possible, and as quickly after arrest as possible. However, in certain circumstances, a person may be held for a prolonged period if a magistrate finds by clear and convincing evidence that the person presents a danger to himself, others, or to property.  In three cases captioned as State v Knoll, the North Carolina Supreme Court decided that if a person is improperly detained or prevented from having witnesses come to the jail to observe him while detained, and the person's case has been prejudiced by the jailer's actions, the person may be entitled to relief, including up to a dismissal of the DWI case.

Trial Defenses

Certain defenses may be available at trial, depending on the facts of the case.  The prosecutor must prove the case beyond a reasonable doubt.  North Carolina's jury instructions define "beyond a reasonable doubt" as proof that entirely convinces and fully satisfies the judge or jury of the truth of each element of the crime of Driving While Impaired.

DWIs have three elements:

1) Driving or Operation of a Vehicle
2) Upon a road, highway, or public vehicular area
3) While subject to an impairing substance

In wreck or accident cases, the district attorney may lack sufficient evidence to demonstrate that either the person was driving the car, or that the car was being driven on a road, highway, or public vehicular area.  Moreover, the district attorney may be unable to prove that the person didn't drink after the driving ceased, and therefore become impaired after all driving had ended.

In cases where the breathalyzer is close to a .08, a defense attorney may be able to win by showing that the person wasn't impaired at the time of the driving, but that the alcohol concentration rose so that by the time the person was tested on the breathalyzer machine, the person's alcohol concentration exceeded the per se limit.

In other cases, the police may suspect that the person was impaired on a drug or medicine. It is illegal to drive in North Carolina even while impaired on a prescribed medication.  However, in these cases, the judge or jury may doubt the evidence of drug impairment either because there are alternate explanations for what looked to be impaired behavior, or because the state failed to take a sample of blood that could be properly tested.

Sometimes the state simply fails to collect any breath or blood sample at all. In these cases, the state will try to prove the case by showing that the person was "appreciably impaired" by an impairing substance.  Appreciable impairment is noticeable impairment or as the Court of Appeals held in 1985 in State v. Harrington "measurable impairment."

Poorly administered walk-and-turn, one-legged stand, or horizontal-gaze-nystagmus tests may result in clues that are unreliable.  A thorough review of the officer's notes, report, and, if the stop was recorded, video is essential in defending an appreciable impairment case.

Other Strategies

While DWIs fall into particular patterns, each case is unique and presents its own challenges and opportunities.  A thorough and experienced DWI lawyer will consider requesting the breathalyzer video, hiring an expert witness, challenging the reliability of the state's Intox EC/IR II breathalyzer machine, looking into an unreliable officer's pattern of arrests, and interviewing witnesses who believe the client was not impaired.


  1. […] have similarities that mean they can fall into patterns, it does not mean that your particular Raleigh DWI case is going to be resolved in such and such a […]