How Physical and Mental Conditions Impact Field Sobriety Tests in DUI Cases
When Disabilities are Misread: How Physical and Mental Conditions Impact Field Sobriety Tests in DUI Cases
When someone is stopped for suspected impaired driving in Pima County or anywhere in Arizona, law enforcement often relies heavily on field sobriety tests (FSTs) to build their case. These roadside evaluations are designed to assess whether a driver is impaired by alcohol or drugs, but what many people don't realize is that these tests come with significant limitations—particularly when the individual being tested has a physical or mental disability.
As a DUI defense attorney in Tucson, I have seen firsthand how assumptions about impairment based on FST performance can lead to unfair conclusions. Many of these assumptions ignore the reality that individuals with legitimate medical conditions may not be able to perform these tests in a "standard" way, even when they are stone-cold sober. Understanding the origins of field sobriety tests and their limitations is crucial to ensuring justice for every defendant.
The Origins of Standardized Field Sobriety Tests
Field sobriety tests were developed in the 1970s by the National Highway Traffic Safety Administration (NHTSA) as part of an effort to create standardized, validated procedures to help officers determine whether a driver might be impaired. The three most commonly administered FSTs are:
The Horizontal Gaze Nystagmus (HGN) test
The Walk-and-Turn (WAT) test
The One-Leg Stand (OLS) test
These tests were tested under controlled conditions on a limited group of individuals and were meant to predict a blood alcohol concentration (BAC) of 0.10% or higher. Eventually, the studies were used to justify a lower threshold of 0.08%, but the original studies had significant limitations that still affect their reliability today.
Notably, the validation studies excluded individuals with physical disabilities, neurological disorders, and many forms of mental illness. In other words, the FSTs were designed and validated for a very specific kind of subject: healthy, able-bodied individuals without pre-existing conditions. So what happens when someone who doesn't fit that mold is asked to perform these tests on the side of the road, often under stressful and unfamiliar conditions?
The Problem with a "One-Size-Fits-All" Approach
The biggest problem with field sobriety tests is that they assume every person has the same baseline ability to balance, follow instructions, and process information under pressure. That assumption is simply not true. A wide range of physical and mental health conditions can affect a person's performance on these tests, even if they are not under the influence of any substance.
For example, individuals with balance issues caused by inner ear problems, past concussions, or musculoskeletal conditions may struggle with the Walk-and-Turn or One-Leg Stand. Someone with a history of anxiety, PTSD, or ADHD may have difficulty focusing on the instructions or performing tasks that require divided attention. Vision disorders, vestibular issues, and even migraines can cause symptoms that an officer might mistake for signs of intoxication.
Even more troubling is the fact that the stress of being stopped by law enforcement—especially at night, with flashing lights and the pressure of knowing you're being evaluated—can exacerbate these existing conditions. For someone with cognitive impairments or traumatic brain injuries, processing multi-step commands and executing them under pressure can be almost impossible.
Real-World Conditions vs. Laboratory Conditions
The original studies validating FSTs were conducted under ideal conditions: smooth pavement, controlled lighting, cooperative participants, and trained evaluators. But DUI investigations rarely happen in ideal settings. More often than not, the tests are administered on uneven road shoulders, in the dark, with traffic whizzing by and an officer standing just feet away watching your every move.
In the real world, these added stressors compound the challenges faced by individuals with disabilities. A test that might be challenging for anyone becomes nearly impossible for someone whose physical or cognitive limitations make them more susceptible to confusion, imbalance, or fatigue.
When Disability Is Misinterpreted as Impairment
The law allows officers to use their observations and training to determine whether someone is impaired, but when those observations are rooted in flawed assumptions about human ability, the conclusions can be deeply problematic. Many officers are not trained to distinguish between signs of physical disability and signs of intoxication. For instance, horizontal gaze nystagmus can occur due to various medical and neurological conditions, yet it is often treated as a definitive indicator of alcohol or drug impairment.
Similarly, slurred speech, delayed responses, and confused behavior can all be symptoms of stroke, neurological injury, or mental health conditions. When these symptoms are taken out of context and interpreted only through the lens of impairment, innocent people can be wrongly accused and prosecuted.
What This Means for DUI Defense
As a defense attorney, it is my job to scrutinize every aspect of the DUI investigation. That includes asking whether the field sobriety tests were fairly administered and whether the officer took into account any existing medical or psychological conditions that could have affected performance. In many cases, we work with medical professionals and expert witnesses to demonstrate that what the officer perceived as "failing" the test was actually a result of a known, documented disability.
It is also important to recognize that a DUI case is not built on FSTs alone. Prosecutors must still prove beyond a reasonable doubt that the individual was impaired at the time of driving. If the only evidence of impairment comes from subjective observations during a roadside test, and we can show that those observations are just as consistent with a medical condition as they are with intoxication, then there is reasonable doubt.
Legal Protections and the Importance of Individualized Evaluation
Every person has the right to be treated fairly and not judged by a system that fails to account for their individual circumstances. When a person with a disability is arrested for DUI based solely on FST performance, without proper consideration of how their condition might affect that performance, it raises serious questions about due process.
Arizona law allows for accommodations and alternative approaches when disabilities are involved, but those protections mean little if officers don’t recognize or inquire about the need for accommodations. In some cases, individuals may not even be aware that their medical condition is affecting their performance in a way that appears incriminating.
This is why it is so important to work with a defense attorney who understands how these nuances can impact a DUI case. An experienced attorney will ask the right questions, seek the right documentation, and challenge assumptions that don’t hold up under scrutiny.
Final Thoughts: Everyone Deserves a Fair Evaluation
Field sobriety tests are not perfect. They were never designed to account for the full range of human experience and ability, yet they are treated by many in law enforcement as near-conclusive evidence of impairment. This is a dangerous oversimplification, especially for individuals living with physical or mental disabilities.
If you or a loved one are facing DUI charges in Tucson or Pima County, and you believe that a disability or medical condition may have affected the outcome of the investigation, I encourage you to reach out. Every case is unique, and your defense should reflect the full story—not just what was observed on the side of the road.
I’m Amanda Bynum, a DUI defense attorney based in Tucson. My job is to protect your rights, question faulty assumptions, and make sure your voice is heard. Let’s talk about how we can fight back—together.
