What is a Standardized Field Sobriety Test?

July 14, 2020

The standardized field sobriety test (SFST) is a test performed by police all over the country to help determine if a driver is either impaired by alcohol or by other means. Though drunk driving laws differ from state to state, the SFST is normally admissible in court in driving under the influence (DUI/DWI) cases.

The SFST consists of a horizontal gaze nystagmus test (HGN) test, a walk-and-turn test, and a one-leg-stand test. During each, the officer conducting the test observes several actions or reactions of the driver. Customarily, the SFST depends on a breathalyzer test to determine the driver’s blood-alcohol concentration (BAC) level.

What is the Horizontal Gaze Nystagmus Test?

During the HGN test, the officer is observing the driver’s eye movement using a small flashlight or a pen. The officer moves the object in slow horizontal movements as the driver is asked to follow the object with just his or her eyes.

The nystagmus is an involuntary sudden movement of the eyeball at peripheral extremes, which causes more exaggerated movements while intoxicated. The officer also checks if the eyes do not move smoothly through the process.  According to the National Highway Traffic Safety Administration (NHTSA), around 88 percent of drivers who have a BAC level of 0.08 or higher fail this test.

What is the Walk-and-Turn Test?

The walk-and-turn test is a divided attention test, which reviews the subject’s actions through commands.

During the walk-and-turn test, the driver is asked to take nine steps in a straight line while touching heel to toes. The subject then turns around on one foot and repeats the process. There are eight things the officer will observe:

  • Lack of balance
  • Disregard of instructions
  • Beginning before instructions are given
  • Failing to touch his or her heel to toes
  • Failing to walk in straight line
  • Incorrect number of steps
  • Improper turning

What is the One-Leg-Stand Test?

The one-leg-stand test is also a divided attention test. The driver must stand on one foot that is six inches off the ground and recite numbers. This lasts normally around 30 seconds, and the officer will check for swaying, hopping, and improper balance.

Approximately 65 percent of drivers who fail two or more indicators will have a BAC level of 0.10 or higher, according to the NHTSA.

What Factors Affect a Sobriety Test?

Different states administer different tests. In terms of admissibility in court, these tests must be proven valid by the officers performing the tests. Some states do not allow non-standardized field sobriety tests.

If someone fails an administered SFST, most likely he or she will be asked to take a breathalyzer. There are many reasons why someone could fail a SFST, such as a disability, the weather, lighting, loud environments, and more. Also, if proper protocols were not followed, one may have a chance in court to prove his or her innocence by contacting an experienced criminal law attorney.

West Chester DUI Defense Lawyers at the Law Offices of Heather J. Mattes Defend Those Accused of Drunk Driving

Getting a DUI charge can have serious consequences on your driving record, career, and future. If you have a DUI charge, it is in your best interests to contact one of our West Chester DUI defense lawyers at the Law Offices of Heather J. Mattes. Call us at 610-431-7900 or complete our online form for a free consultation. Located in West Chester, Pennsylvania, we proudly serve clients throughout Chester County, Bucks County, Delaware County, Lehigh County, Montgomery County, and Philadelphia County.

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