If you are pulled over for driving while impaired (DUI), the police officer may ask you to get out of the car and do a set of physical and mental chores called field sobriety tests (FSTs). These tests are intended to help law enforcement determine whether you’re impaired. But how accurate are they really? And can the results be trusted in a court of law?
What Are Field Sobriety Tests?
Field sobriety tests are standardized assessments developed by the National Highway Traffic Safety Administration (NHTSA). The three most commonly used tests include:
- Horizontal Gaze Nystagmus (HGN) – The cop watches the driver’s eyes as they follow a moving object to see if they jerk uncontrollably, which could mean they aren’t thinking straight.
- Walk-and-Turn (WAT) – The individual must walk heel-to-toe in a straight line, turn on one foot, and walk back, following verbal instructions.
- One-Leg Stand (OLS) – For a certain amount of time, the person stands on one leg and counts out loud.
While these tests are widely used and considered “standardized,” their reliability can be affected by many factors.
Factors That Affect Accuracy
FSTs rely heavily on subjective observation. Police are taught to look for “clues” that someone is drunk, like stumbling, slurred speech, or having trouble keeping their balance. However, these signs can be influenced by a wide range of non-alcohol-related factors:
- Medical conditions like inner ear issues, neurological disorders, or anxiety can affect balance and coordination.
- Physical injuries or age-related conditions may make it hard to perform the walk-and-turn or one-leg stand.
- Environmental conditions like uneven ground, bad lighting, or bad weather can make performance worse.
- Wearing boots or high heels can make it harder to keep your balance or walk straight.
Even something as simple as nerves—especially when someone is being scrutinized by police—can cause a completely sober person to perform poorly on these tests.
The Margin of Error
According to NHTSA studies, the HGN test is about 77% accurate, the walk-and-turn about 68%, and the one-leg stand around 65% in detecting blood alcohol levels over the legal limit. While that may seem reasonably reliable, it also means that officers can misinterpret the results in more than 1 out of 3 cases for some tests.
This is particularly concerning for drivers facing DUI charges based primarily on FST results. In fact, many DUI defense attorneys argue that these tests alone should not be the sole basis for arrest or conviction.
Challenging Field Sobriety Tests in Court
If you’ve been charged with a DUI based on a failed FST, it’s possible to challenge the results in court. A knowledgeable defense attorney will examine whether the officer administered the tests correctly, whether external factors affected your performance, and whether the arresting officer had the proper training.
For example, a case in Gilbert involved a driver who was pulled over late at night and asked to perform field sobriety tests in a poorly lit area with uneven gravel. Though the officer believed the driver showed signs of impairment, the defense attorney argued that the conditions unfairly impacted the results. The charges were ultimately reduced.
Conclusion: Not Always Black and White
To be fair, field balance tests are helpful for police, but they are not perfect. The results depend on both the circumstances of the stop and the interpretation of the officer. If you or someone you know has been arrested for DUI based primarily on field sobriety tests, it’s essential to understand your rights and options.
An experienced DUI attorney in Gilbert can evaluate the validity of the tests used in your case and help protect your legal interests, especially if the stop occurred under questionable conditions, such as those often seen in Gilbert and surrounding areas.
Understanding the limitations of FSTs is crucial in ensuring that justice isn’t compromised by flawed or incomplete evidence.
