Have you ever wondered how police officers determine if a driver is under the influence of alcohol? One of the most common methods they use is the horizontal gaze nystagmus (HGN) test. Understanding what the HGN test is and its effectiveness in detecting impairment is essential.
What is the HGN Test?
The HGN test examines involuntary eye movements. Nystagmus refers to the rapid, uncontrollable jerking of the eyes when they rotate at high peripheral angles.
While everyone experiences nystagmus to a degree, alcohol consumption can exaggerate this effect, making it more noticeable at lower angles.
When subjected to an HGN test, the officer may ask you to follow a small object with your eyes while your head is still. They will then look for specific clues. If they observe four or more clues, they may consider it a strong sign of impairment.
How effective is the HGN test?
Research has shown that the HGN test is a reliable field sobriety test. According to the National Highway Traffic Safety Administration, it accurately detects drivers with a blood alcohol concentration (BAC) of 0.10 or higher. However, it is essential to note that the test is not foolproof.
Medical conditions, including inner ear disorders or certain eye diseases, may cause nystagmus unrelated to alcohol consumption. Additionally, the test’s accuracy may depend heavily on the officer’s training and proper administration.
While the HGN test is valuable in identifying potential impairment, law enforcement typically uses it with other field sobriety tests and breathalyzer results to build a stronger case to make a driving under the influence (DUI) arrest.
If law enforcement officers require you to perform this test, you may have the right to refuse, though this may lead to other consequences depending on your local laws. You may want to consult an attorney to help you understand your rights and legal options.