Not every city has a great public transportation system for getting people home after a night out. However, driving yourself home after a night of drinking because your designated driver took off on you won't win over a judge. If you see those unmistakable red and blue lights in your rear view mirror after you've been drinking, you'll probably have a few questions about the types of tests the officer uses to determine if you are driving over the legal blood alcohol limit. Below, you will find a discussion of field sobriety tests.

Basics of Field Sobriety Tests

Field sobriety tests, sometimes called roadside sobriety tests, are used to enforce DUI laws and usually precede Breathalyzer tests. A police officer typically performs a three-part field sobriety test after a traffic stop where there is suspicion that the motorist may be drunk or otherwise impaired. These tests allow an officer to observe a suspect's balance, physical ability, attention level, or other factors that the officer may use to determine whether the suspect is driving under the influence.

Officers record the suspect's performance on a field sobriety test to be used as evidence in DUI cases; such tests generally have been upheld on appeal. The purpose of all sobriety tests is to ensure that a police officer has probable cause to arrest someone for driving under the influence.

Standardized Field Sobriety Tests

The Standardized Field Sobriety Test (SFST) endorsed by the National Highway Traffic and Safety Administration (NHTSA) consists of the horizontal gaze nystagmus (HGN), walk-and-turn (WAT) and one-leg stand (OLS):

Horizontal Gaze Nystagmus: This term refers to the involuntary jerking of the eye that occurs naturally when the eye gazes to the side. But this jerking (or nystagmus) is exaggerated when someone is impaired by alcohol. Officers look for three indicators of impairment in each eye: inability to follow a moving object smoothly; distinct eye jerking when eye is at maximum deviation; and eye-jerking within 45 degrees of center.

Walk and Turn: The purpose of this test, determined to be easily done by most unimpaired people, tests the suspect's ability to complete tasks with divided attention. This is administered by requiring the suspect to take nine steps, heel-to-toe, along a straight line; turn on one foot; and then return in the same manner in the opposite direction.

One-Leg Stand: Suspects are asked to stand with one foot about six inches off the ground and count for 30 seconds. Swaying while balancing, using arms to balance, hopping or putting the foot down indicate possible impairment.

Taken as a whole, the three components of the SFST accurately indicate alcohol impairment in 91 percent of all cases and 94 percent of cases if explanations for some of the false positives are accepted, according to a 1998 study cited by the NHTSA. Suspects who fail the field sobriety test usually are given a breathalyzer test to determine their blood-alcohol concentration before an arrest is made.

Non-Standardized Field Sobriety Tests

Other, non-standardized field sobriety tests may include one or more of the following: standing with feet together and tipping the head backwards; counting the number of fingers an officer raises; reciting the alphabet; counting backwards; standing and leaning back to look up at the sky while holding arms to the side; or closing the eyes and touching nose with finger.

Get a Better Understanding of Field Sobriety Tests by Speaking to a Lawyer

The field sobriety test is one of several different techniques used by police to determine probable cause for a DUI arrest. But if it was not conducted properly, there's a chance the charges could be dropped in certain instances. For this and other reasons, it's important to get critical feedback from a legal professional. Learn more by speaking to an experienced DUI attorney near you today.