Law enforcement officers in all 50 states utilize Standardized filed sobriety tests (SFSTs) to determine the impairment of a person’s driving due to alcohol influence. The SFSTs are comprised of a battery of three tests: 1) Horizontal Gaze Nystagmus test (HGN), 2) Walk and Turn Test (WAT) and 3) One Leg Stand Test (OLS). For a more in-depth explanation of these SFSTs click

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The National Highway Traffic Safety Administration (NHTSA) developed these SFSTs and is in charge of training law enforcement personnel on the procedures of the SFSTs. NHTSA conducted a series of scientific research studies to determine the accuracy of the SFSTs. After collecting data from these studies, NHTSA analyzed the laboratory data and found:

• HGN—by itself, was 77% accurate
• WAT—by itself, was 68% accurate
• OLS—by itself, was 65% accurate
• By combining HGN and WAT and 80% accuracy can be achieved.

One can therefore see from the results above, that even if the proper procedures are followed by officers conducting the SFST, these filed tests are at best 80% accurate in determining the impairment of drivers.

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