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Field Sobriety Test

Field Sobriety Tests

The National Highway Traffic Safety Administration (NHTSA) has established very specific guidelines that police officers must follow when administering and scoring field sobriety tests. The NHTSA field sobriety test that Missouri police officers most frequently utilize is comprised of three divided attention tests to help a police officer determine if a driver is impaired. These tests include horizontal gaze nystagmus (HGN), one-leg stand, and walk-and-turn tests.

Horizontal Gaze Nystagmus (HGN) Test

Before administering the HGN test, a police officer is supposed to check your eyes for possible medical impairment. Next, the officer must check your eyes to make sure your pupils are of equal size and can track equally. The officer is also supposed to check for resting nystagmus.

If a driver is eligible to take the HGN test, the officer can then proceed to administer the test. An officer administering the HGN test uses a stimulus in a series of passes in front of the driver’s eyes looking for an involuntary jerking as they gaze toward the side. According to NHTSA, an involuntary jerking is a sign of intoxication. The HGN test measures the involuntary jerking of the eyes with three clues. Those clues are lack of smooth pursuit, distinct nystagmus at maximum deviation, and onset of nystagmus prior to 45 degrees. Each of these clues are distinct steps that must be tested by the officer in order for the HGN test to be valid.

One-Leg Stand Test

The one-leg stand (OLS) test is a divided attention test that divides the driver’s attention between mental and physical tasks. There are two components to the OLS test: the instructions component and the balance and counting component. The instructions stage of the test is designed to divide the driver’s attention by having the subject stand with feet together, keeping both arms at the sides, while listening to instructions. The officer must physically demonstrate each individual instruction given to the driver.

The driver must be told to hold the foot of his or her choice approximately 6 inches off the ground in front of the body, point his or her toe forward, keep both legs straight, keep his or her arms down to the sides, watch the raised foot, and to count out loud until told to stop. The officer should tell the driver to pick his or her foot up if it comes down and resume counting where he or she left off. The officer must terminate the test after 30 seconds. The four clues the officer is looking for on this test are: (1) using arms for balance; (2) swaying while balancing; (3) putting foot down during test; and (4) hopping.

Walk-And-Turn Test

Like the one-leg stand test, the walk-and-turn test (WAT) is a divided attention test that divides the driver’s attention between mental and physical tasks. Before administering the WAT, the officer must ask the driver if he or she has any physical problems or disabilities. Assuming the driver is eligible to perform the walk-and-turn test, the officer must then provide detailed instructions accompanied by demonstrations of each individual instruction.

The driver must initially be told to stand with his or her right foot in front of the left foot, touching heel-to-toe, arms down to the sides, to remain in that position, and not to start the test until told to do so. This is the instructional phase of the WAT. Then, the driver must be told to take nine heel-to-toe steps on a designated line, and when reaching the ninth step, the driver must leave his or her lead foot planted, take a series of small steps around to the left with his or her other foot, and then take nine (9) heel-to-toe steps back down the designated line. The police officer must demonstrate the test, ask the driver if he or she understand the instructions, and then score the driver’s performance.

Contact a St. Louis DWI Lawyer Today

At Henderson Law Group, we handle cases ranging from a first-time DWI offense to felony DWI cases throughout Missouri and Illinois. Our experienced DWI lawyers understand this complex area of law, and know what steps to take to protect your rights. We will work tirelessly to obtain the best possible result for you. Contact us today for a free consultation. We are available 24 hours a day, 7 days a week.