Standardized Field Sobriety Tests (SFSTs) in a DUI Investigation
What are the Standardized Field Sobriety Tests (SFST’s) used in a DUI Arrest?
These are roadside tests used by law enforcement officers to assist them in determining if there is probable cause to arrest a person for driving under the influence (DUI). These tests have been “scientifically validated” by numerous studies sponsored by the National Highway Traffic Safety Administration (NHTSA). These field sobriety test validation studies will be covered in more detail in a later article.
There are (3) standardized elements to the SFST’s:
Standardized Administrative Procedures
All officers must administer the SFST’s the same way every time.
Standardized Clues
All officers must look for the same clues on each test.
Standardized Criteria
All officers must use the same criteria to determine if a clue is present.
The (3) standardized field sobriety tests are:
Horizontal Gaze Nystagmus (HGN)
Walk and Turn
One Leg Stand
Horizontal Gaze Nystagmus is the involuntary jerking of the eyes as they look to the side. It is caused by alcohol, and certain other drugs. There are (3) clues officers are trained to look for in HGN:
Lack of Smooth Pursuit
Distinct and Sustained Nystagmus at Maximum Deviation
Onset of Nystagmus Prior to 45 Degrees.
The clues are checked for in both eyes of the subject, meaning a total of (6) clues are possible to see during the HGN. Based on validation studies and research officers are trained on, if an officer observes 4 or more clues, it indicates that the person’s blood alcohol concentration (BAC) is 0.08 grams or higher. Research studies cited by law enforcement state that this test is 88% accurate.
The Walk and Turn test is a divided attention test, meaning that the test “divides” a person’s attention between mental and physical tasks. This is significant because safe driving demands the ability to divide attention between multiple mental and physical tasks. Imagine how everyday driving divides your attention: maintaining your lane while being aware of other vehicles' position, maintaining proper speed, safely making movements, proper signaling, etc. There are 2 phases and 8 standardized clues for the Walk and Turn test:
Instructional Phase
Unable to keep balance while listening to instructions
Starts too soon
Walking Phase
Steps off line
Misses heel to toe
Incorrect number of steps
Improper turn
Raises arms for balance
Stops to balance self
Based on research cited by law enforcement, if an officer observes 2 or more clues it indicates that the person’s blood alcohol concentration (BAC) is 0.08 grams or more. The validation studies state that this test is 79% accurate.
The One Leg Stand test is the second divided attention test used as part of the 3 test battery. There are 2 phases and 4 clues for the One Leg Stand:
Instructional Phase
No clues
Walking Phase
Puts foot down
Sways
Hops
Raises arms for balance
Based on the research if an officer observes 2 or more clues it indicates that the person’s blood alcohol concentration (BAC) is 0.08 grams or more. The research states that this test is 83% accurate.
When the tests are combined, the validation studies cited by law enforcement state that they are 91% accurate. These tests can, of course, provide strong evidence and assist the prosecution with convicting a person accused of DUI when done properly.
In the next article, the administrative procedures and issues that can arise with HGN will be covered.
About the author: Joshua Ott was a police officer for more than 10 years in Roswell, Georgia. He has extensive experience dealing with impaired drivers. He was a Drug Recognition Expert Instructor and is a Standardized Field Sobriety Testing Instructor and has trained numerous officers over the course of his career. He now operates Caselock, Inc, which provides expert testimony and case reviews for cases involving alcohol and drug impairment. Visit his website at caselockinc.com.