When police officers pull someone over on suspicion of drunk driving, they may not give them a breath test right away. Instead, officers may ask a motorist to perform field sobriety tests, which are designed to expose impairment. If someone struggles with the tests, then the officers may arrest them and/or have them take a breath test.
The three main field sobriety tests commonly used by law enforcement to assess whether a driver is impaired are as follows:
- Horizontal Gaze Nystagmus (HGN) Test: In this test, an officer will ask the suspect to follow an object, usually a pen or a small flashlight, with their eyes. The officer looks for signs of nystagmus, which is a jerking movement – and an involuntary reaction – involving the person’s eyeball itself. This happens when they look to the side. If that person is impaired by alcohol, a smaller angle may trigger this reaction because the nystagmus gets exaggerated.
- Walk-and-Turn Test: This test focuses on splitting a person’s attention between two tasks. This allows the officer to assess the suspect’s ability to complete tasks requiring both mental and physical ability. The suspect must walk a set amount of steps in a straight line, touching their heel against their toe. When they reach the end, they turn on one foot and come back. The officer looks for signs of impairment, such as starting before the instructions are finished, falling off of the line or a general inability to maintain balance.
- One-Leg Stand Test: Another “divided attention” test, where the suspect is asked to stand with one foot slightly off the ground and count off seconds until told to put their foot down. The officer may also time the subject so that they do this for at least 30 seconds. They could fail if they sway back and forth, set one foot down or fall over.
These tests are designed to measure a person’s balance, coordination and their ability to divide attention among more than one task, as these abilities are often impaired by alcohol or other substances.
Do these tests work?
The problem with these tests is that, while they can work, they are far from perfect and often provide inaccurate results. For instance, one study carried out by the National Highway Traffic Safety Administration (NHTSA) found that the one-leg stand test had an accuracy rate of just 65%. For every two people who were impaired, police may have arrested one person who also failed the test without any impairment. The other tests are slightly better, but not flawless. The walk-and-turn test comes in at 68% and the HGN test hits 77%.
If you failed a sobriety test during a stop, don’t assume that means you will be convicted of the impaired driving charges that you’re likely facing now. Seeking legal guidance can help you clarify your rights, options and the defensive strategies available to you at this challenging time.