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Just How Accurate Is a Standardized Field Sobriety Test?

Standardized field sobriety tests (SFSTs), as they're known, are intended to provide officers with a reliable indicator of driver impairment due to alcohol or drugs. However, beneath the veneer of objectivity lies a complex reality: SFSTs, while valuable tools, are not infallible.

Overview of Standardized Field Sobriety Tests (SFSTs)

When a driver is pulled over on suspicion of impaired driving, law enforcement officers often rely on Standardized Field Sobriety Tests to gauge their level of intoxication. There are multiple types of SFSTs, including:

  • The Horizontal Gaze Nystagmus (HGN) test involves tracking the movement of the driver's eyes to spot involuntary jerking, which can be a sign of intoxication.
  • The Walk-and-Turn (WAT) test assesses the driver's ability to follow instructions and maintain balance while walking a straight line and turning.
  • The One-Leg Stand (OLS) test requires the driver to stand on one foot without swaying or using arms for balance. These tests are supposed to measure coordination and balance as well as the ability to follow directions, which can be compromised by alcohol or drug consumption.

Explanation of Scoring Criteria & Pass/Fail Thresholds

Each SFST has specific scoring criteria that officers use to determine whether a driver passes or fails. The HGN test, for example, has a series of indicators, such as lack of smooth pursuit or distinct nystagmus at maximum deviation. The WAT and OLS tests have point systems based on the number of balance and coordination errors made by the driver.

A certain number of points or observed indicators can lead to a failed result, which may then contribute to the officer's decision to arrest the driver for suspected DUI/DWI. It's important to note that these thresholds are not foolproof and can be influenced by various factors, which we will explore in the following sections.

Research from the NHTSA found that these standardized tests were not 100% accurate. In fact, the horizontal gaze nystagmus demonstrated a 77% accuracy rate, the walk and turn exhibited a 68% accuracy rate, and the one-leg stand showed a 65% accuracy rate. When all three tests were employed in conjunction, they yielded correct results 82% of the time.

Factors Influencing Test Reliability

Impact of Individual Officer Training & Experience on Test Administration

The accuracy of SFSTs is heavily dependent on the training and experience of the administering officer. The walk and turn test is notorious for resulting in false positives when the instructions are unclear.

Officers who have undergone thorough training in SFST administration are more likely to conduct the tests correctly and interpret the results accurately. However, variations in training quality across different jurisdictions can lead to inconsistencies in how officers administer the tests.

An officer's experience with SFSTs also plays a crucial role, as seasoned officers may be better at detecting subtle signs of impairment that less experienced officers might overlook. This variability in test administration can have significant implications for the reliability of the results.

Environmental & Roadside Conditions Affecting Test Performance

Environmental factors can also impact the reliability of SFSTs. Conditions like uneven pavement, poor lighting, or inclement weather can affect a sober driver's ability to perform the tests, potentially leading to false positives.

Additionally, roadside distractions like passing traffic or noise can interfere with a driver's concentration and balance. These external variables must be considered when evaluating the accuracy of SFST results, as they can skew the outcome and may not accurately reflect a driver's level of impairment.

The Driver's Physical & Mental Condition

The driver’s physical and mental condition at the time of testing can significantly affect the results. Certain medical conditions, injuries, or disabilities may impede the driver's ability to perform the physical tasks required by the tests. Fatigue, anxiety, or stress can also impact the driver's performance, potentially leading to false positives. For example, the horizontal gaze nystagmus (HGN) test, which assesses involuntary eye movements, is prone to false positives if the driver has naturally occurring nystagmus or if the test is improperly administered.

Challenging Field Sobriety Test Results

In legal proceedings, it is essential for defense attorneys to be aware of the potential weaknesses of SFSTs and to be prepared to challenge their reliability. By highlighting the various factors that can influence test results, attorneys can effectively question the validity of the evidence presented by the prosecution. This may involve presenting expert testimony to refute the accuracy of the tests under specific circumstances or to demonstrate the lack of standardized testing conditions.

Call (865) 544-2010 to Talk with Our Team

At Eldridge and Cravens, PC, we can help those facing driving under the influence (DUI) charges. Our team can review the details of your case and help you develop a customized defense, whether that involves challenging the validity of your SFSTs, the results of a blood test, the accuracy of breathalyzer results, or aspects of the stop and arrest.

Request a complimentary case consultation today!