Field sobriety tests (FSTs) are common tools used by police officers to assess impairment during traffic stops. While they may seem scientific, their accuracy depends on several factors. Understanding the limitations of these tests can help you recognize their potential flaws.
Standardized vs. non-standardized tests
The National Highway Traffic Safety Administration (NHTSA) has approved three standardized field sobriety tests: the Horizontal Gaze Nystagmus (HGN), the Walk and Turn, and the One-Leg Stand. These tests are designed to be consistent, but results can still vary. Non-standardized tests, such as counting backward or reciting the alphabet, have even less reliability. Officers may interpret results differently, leading to inconsistent conclusions.
Factors that affect test results
Many factors can influence how someone performs on an FST. Poor balance, nervousness, medical conditions, or even the type of shoes you are wearing can impact the outcome. Additionally, roadside conditions such as uneven pavement, poor lighting, and traffic noise can make the tests more difficult. Officers might not always consider these factors, which could affect the assessment.
Subjectivity in officer interpretation
Even with standardized procedures, an officer’s observations play a major role in determining the outcome. Differences in training, experience, and situational factors can influence the results. Unlike breath or blood tests, FSTs do not provide numerical measurements, which may make assessments more open to interpretation. Providing additional evidence can help clarify the results.
How reliable are these tests?
Studies suggest that even standardized FSTs are not 100% accurate. The HGN test has the highest reliability but still has a margin of error. The Walk and Turn and One-Leg Stand tests have lower accuracy rates. This means sober individuals can fail, and impaired individuals can pass, making these tests less reliable than they seem.
