Driving under the influence (DUI) is a serious offense in California, and law enforcement uses several methods to assess whether a driver is impaired. One of the most commonly used field sobriety tests in DUI cases is the Horizontal Gaze Nystagmus (HGN) test. This test is designed to detect involuntary jerking movements of the eye, known as nystagmus, which can occur when a person is intoxicated. However, it's important to understand that the HGN test has its limitations and is not always reliable. This article explores the intricacies of the HGN test, how it's administered, its legal implications, and how it can be challenged in court.

What is the Horizontal Gaze Nystagmus (HGN) Test?

The HGN test is one of three standardized field sobriety tests (SFSTs) validated by the National Highway Traffic Safety Administration (NHTSA). The other two tests are the Walk and Turn test and the One-Leg Stand test. The HGN test specifically measures involuntary jerking movements of the eyes, which may indicate impairment due to alcohol or drugs.

Key Points:

• Involuntary eye movement (nystagmus) becomes more pronounced when intoxicated.
• NHTSA considers the HGN test to be a reliable indicator of impairment, but it is not foolproof.
• The California Vehicle Code Section 23152 prohibits driving under the influence, and field sobriety tests are often used to gather evidence of intoxication.

How is the HGN Test Performed?

The HGN test involves the police officer instructing the driver to follow a stimulus (usually a pen or small flashlight) with their eyes while keeping their head still. The officer moves the object from side to side and observes the movement of the driver's eyes.

Steps of the HGN Test:

1. Verbal Instructions: The officer instructs the driver to keep their head still, look at the object, and follow it with their eyes.
2. Stimulus Position: The object is held about 12 to 15 inches from the driver's nose.
3. Eye Movement Observation: The officer moves the object slowly from side to side, watching for signs of nystagmus.

Three Major Clues of Intoxication

During the test, the officer looks for three main clues of intoxication in each eye, making a total of six possible clues:

1. Lack of Smooth Pursuit: The eyes cannot smoothly follow the object.
2. Distinct Nystagmus at Maximum Deviation: The eyes begin to jerk distinctly when looking as far to the side as possible.
3. Onset of Nystagmus Before 45 Degrees: The eyes start to jerk when the object is less than 45 degrees from the center.

If the officer observes at least four out of six clues, they may conclude that the driver has a blood alcohol content (BAC) of 0.08% or higher, which is above the legal limit in California under California Vehicle Code Section 23152(b).

Important Details:

• Timing and Procedure: The object should be moved at a specific speed (about two seconds out and two seconds back), and the officer must hold the object at maximum deviation for at least four seconds.
• Technical Requirements: The officer must follow strict technical guidelines, including maintaining the correct distance and angle of the stimulus.

Legal Issues Surrounding the HGN Test

While the HGN test is widely used, it is not without controversy. California courts have recognized the HGN test as a potentially reliable indicator of impairment, but the test must be administered properly. If not conducted according to the guidelines set forth by the NHTSA, the results may be inadmissible in court.

Key Legal Points:

• California Evidence Code Section 720 requires that an expert witness must establish the scientific validity of the test in court.
• The California Vehicle Code Section 23152(f) also includes drug impairment, and HGN tests are used to detect intoxication from both alcohol and drugs.
• If the test is improperly administered, it may violate the driver's rights under California Penal Code Section 1538.5, which allows for suppression of improperly obtained evidence.

Common Challenges to the HGN Test

A skilled DUI defense attorney can challenge the results of an HGN test by questioning its administration, reliability, and the officer's training. Here are some common challenges:

Unreliable Administration:

• Subjectivity: The officer's judgment of eye movement is subjective, leading to possible bias.
• Improper Procedure: Failure to adhere to NHTSA guidelines can make the results unreliable.

External Factors Affecting Results:

• Environmental Issues: Poor lighting, weather conditions, or distractions (such as flashing police lights) can affect the accuracy of the test.
• Health Issues: The driver may have a pre-existing medical condition (such as an eye disorder, ear disorder, or head injury) that causes nystagmus unrelated to intoxication.

Non-Alcohol-Related Causes of Nystagmus:

• Medical Conditions: Certain medical conditions, including brain injuries, inner ear infections, or neurological disorders, can cause involuntary eye movements.
• Medications: Drugs such as antihistamines, barbiturates, or certain prescription medications can cause nystagmus, even if the driver is not impaired by alcohol.

How to Fight a DUI Charge Based on the HGN Test

Challenging the HGN test in court can be an effective strategy for defending against DUI charges. A DUI defense attorney may:

• Question the Officer's Training: Ensure the officer was properly trained in administering the HGN test.
• Challenge the Conditions: Argue that environmental conditions or the driver's health affected the test results.
• Prove Improper Administration: Demonstrate that the test was not conducted in accordance with NHTSA guidelines, making the results unreliable.

Legal Strategies:

• Cross-examine the officer: Questioning the officer's experience and training can reveal weaknesses in the test's administration.
• Use expert witnesses: A defense expert can testify about the scientific unreliability of the HGN test and other potential causes of nystagmus.
• File a motion to suppress: Under California Penal Code Section 1538.5, evidence from an improperly administered test may be excluded from the trial.

Conclusion: Know Your Rights and Defenses

The HGN test is a tool law enforcement uses to detect intoxication, but it is far from infallible. If you have been arrested for DUI in California and the HGN test was used against you, it's important to understand your legal rights and options. An experienced DUI defense attorney can thoroughly investigate the circumstances surrounding your arrest, including how the HGN test was administered, and build a strong defense on your behalf.

Contact the Law Office of John Campanella

At the Law Office of John Campanella, we specialize in defending DUI cases and challenging the validity of field sobriety tests like the HGN test. If you or a loved one has been charged with a DUI, call us at (916) 498-8460 to schedule a free consultation and learn how we can help you fight the charges.