The Science Behind Field Sobriety Tests
Commonly used by law enforcement in Texas and across the U.S., field sobriety tests are used to assess whether a driver is under the influence of alcohol or drugs. Although these tests have been standardized by the National Highway Traffic Safety Administration (NHTSA), their scientific reliability has long been debated. If you believe an outside factor affects the results of your tests, leading to unfair charges, connect with a Houston DWI lawyer.
Are They Really Reliable?
There are three main standardized field sobriety tests. They are designed to measure coordination, balance, and cognitive function, all of which can be impacted by alcohol or drugs.
- Horizontal gaze nystagmus. This test involves an officer observing the eyes as the driver follows a moving object, like a pen or flashlight. Alcohol can cause involuntary jerking in the eyes (nystagmus), but nystagmus can also be triggered by fatigue, certain medications, or neurological conditions, meaning an officer might mistake a natural reaction for impairment.
- Walk-and-turn. To assess the possibility of impairment, a driver is asked to take nine steps along a straight line, turn, and return in the same manner in order to measure balance and coordination. Yet factors like uneven ground, footwear, or anxiety can easily disrupt performance, even if the individual is sober. Physical conditions, such as vertigo or joint pain, can also impact results.
- One-leg stand. Here, the driver must balance on one leg, raising the other foot about six inches off the ground and counting for about 30 seconds. While alcohol can impair balance, other factors such as inner ear issues, muscle fatigue, or even certain shoes (such as high heels or loose-fitting sandals) can make this test challenging for sober individuals.
The reality is that despite their widespread use, field sobriety tests are not foolproof. There have been studies that have shown that the reliability of these tests is mixed. The NHTSA’s own research claims around 77% reliability for the walk-and-turn test and 83% for the one-leg stand, but these percentages still leave room for significant error.
What Can Affect Results?
Several factors unrelated to alcohol consumption can lead to a failed sobriety test. For example, issues like arthritis, inner ear problems, and neurological disorders can impair balance and coordination.
Also, being pulled over and asked to perform in front of an officer can induce anxiety, causing physical shakiness or mental lapses. Likewise, uneven or slippery surfaces can make it difficult to execute balance-focused tasks.
After being accused of being intoxicated and charged with drunk driving based on field sobriety test results, a Houston DWI lawyer can be an essential ally. A skilled attorney can scrutinize the circumstances of the tests administered, question the validity of the results, and highlight any environmental or personal factors that may have affected performance.
Do you want to talk to a legal professional following a drunk driving arrest? Connecting with the attorneys at Ayson Law Firm is a way to protect your rights and ensure that any evidence used against you is critically examined. Contact us today for a confidential consultation.
