Police officers can rely on tests to ascertain whether someone is driving under the influence or not. Here, DUI attorney Claiborne Ferguson of the Claiborne Ferguson Law Firm in Memphis, Tennessee explains what they all mean. His practice is devoted to DUI defense and capital murder cases. Both require a vast knowledge of science and law, which is why he has extensive training in both areas.
The Standardized Field Sobriety test (SFT) is a series of three tests developed by the National Highway Traffic Safety Administration (NHTSA) in order to evaluate valid indicators of impairment or to establish probable cause for arrest under DUI in a standardized way.
A formal program of training was made available to police officers to become more skillful at detecting and arresting subjects who are driving while impaired. They were also trained in presenting testimony which would be effective in conviction of drivers at court. Many DUI defense attorneys have also been trained in the NHTSA’s standard field sobriety test testing.
The main components of the SFT are the Horizontal Gaze Nystagmus (HGN), the walk-and-turn test and the one-leg stand test. In order for the test to be valid, these three tests should be given according to the training provided by the NHTSA. In short, the components are:
1. HGN Testing: Horizontal Gaze Nystagmus is the involuntary twitching of the eye which occurs as the eye moves towards the periphery. When a person has been drinking, this nystagmus may become exaggerated and occur sooner than expected. In the HGN test, the officer will ask a subject to follow a slowly-moving item such as a pen, which will track horizontally followed by the suspect’s eyes until the officer observes the nystagmus, or twitching of the eye. The officer is looking for three main indicators of impairment in each eye.
- First: Whether or not the suspect can follow the slowly moving object with a smooth movement of the eyes.
- Second: Whether the jerking or twitching of the eye occurs at the maximum deviation of the eye.
- Third: If the twitching occurs prior to the onset of a 45-degree angle from center.
If between the two eyes, one or more of the clues appear, it is scientifically indicative of a BAC, or blood alcohol content, of 0.10 or greater, which is above the legal limit of impairment. This test may also indicate the consumption of illegal drugs.
2. Walk-and-Turn Test: This is a test referred to a “divided attention” test, which means that the police are asking a suspect to perform multiple tasks at the same time. These tests are thought to be easily performed by most sober people. But impaired persons may have difficulty with the tasks which require their attention to be divided between simple mental and physical exercises.
The walk-and-turn test asks the suspect to listen and remember instructions, and to not start or begin the test until told to do so. Instructions request the suspect to take nine steps heel-to-toe in a straight line. After the nine steps, he or she is instructed to turn in a certain manner and return in the same direction, again taking nine steps.
The officer is looking for seven indicators of impairment:
- That the suspect cannot keep balance by listening to instructions;
- That the suspect not begin before the instructions are finished;
- That the suspect does not stop or hesitate while taking the nine steps;
- That the suspect does not touch heel-to-toe with each step;
- That the suspect uses the arms to balance;
- That the suspect does not lose balance,
- That the suspect is able to count the correct number of steps.
3. One-Leg Stand: The suspect is instructed to stand with one foot approximately six inches off the ground and count aloud by the thousands until told to put the foot down. The test should last 30 seconds. Based on the performance of the test, the officer decides whether or not it indicates any level of impairment.
