Driving Under the Influence – Different Types of Field Sobriety Tests

After a police officer stops an impaired driver, he administers several field sobriety evaluations. The National Highway Traffic Safety Administration has produced a manual that standardizes these tests. Only when the officer follows the NHTSA’s procedures are the tests likely to be upheld in court.

The Walk and Turn test looks for more than whether you can walk heel-to-toe or on a straight line. The police officer is supposed to score you on eight separate criteria, including the instructional and walking stages. In the instructional phase, the officer scores you on starting too soon or inability to maintain your balance. In the walking phase, the officer notes whether you stop while you are walking, whether you step off the line, do not touch your heels to your toes, raise your arms more than 6 inches away from your body, lose balance as you turn, turn improperly, or you take too many or too few steps. Two clues or more out of the combined eight put you into the failing category.

If the officer asks whether there is any reason you can’t perform the WAT before you know what you will be doing, this invalidates the testing. Leg or back injuries may also invalidate testing.

Horizontal Gaze Nystagmus tests whether your eyes are able to track the officer’s finger or pen smoothly without jerking. The officer looks for six criteria in this test, including lack of smooth pursuit in both eyes; noticeable involuntary eye movement in both eyes; and involuntary eye movement that becomes evident prior to 45 degrees in both eyes. The officer also tests for vertical involuntary eye movement. If you have a positive result for one criteria, you will have positive results for other criteria. If you are scored for four out of six clues, this can indicate a BAC of.08 or higher.

The officer also uses the One Leg Stand, in which you stand on one leg and count while being timed for 30 seconds. As you are taking this test, the officer looks for four criteria, including putting your foot to the ground, raising your arms for balance, hopping or swaying. If you are scored on two or more out of the four criteria, you are considered to have failed the test. If you sway, this may not be an objective indicator of intoxication. Weather, road conditions and traffic may impact the outcome of your testing. The NHTSA considers the OLS to be a better indicator of intoxication.

Law enforcement also uses a handheld device, generally called a Breathalyzer to determine the estimated amount of alcohol in your blood stream. This test has come under sharp criticism because of the belief that the device provides inaccurate or false positive results. The breathalyzer can be extremely sensitive to the presence of alcohol from innocent sources, such as mouthwash. Depending on how you breathe, this can change your results when you blow into the machine. Unfortunately, the officer who stopped you can’t do anything to control for these factors. If you refuse to take a breathalyzer test, your driver’s license may be automatically suspended, even if you are not guilty.