Field sobriety tests are a common investigative tool used by police who suspect a driver of drinking and driving, driving while intoxicated (DWI), drunk driving or driving under the influence (DUI). Drivers often hope they can avoid an arrest by “passing” these tests, but that’s nearly impossible, because they’re designed to be failed. Their sole purpose is to create probable cause to make an arrest and to create evidence to prosecute the driver in court for drunk driving.

Field sobriety tests are designed to prove mental and physical impairment from alcohol and/or drug use by dividing the driver’s attention between two tasks. Prosecutors will use any variation between the way the test is supposed to be taken and the way the driver performed as proof of driving while impaired. However, Fort Bend drunk driving defense lawyer David Hunter will use those same results to show the absence of mental or physical impairment.

All field sobriety tests are not created equal. The National Highway Traffic Safety Administration (NHTSA) has endorsed three standardized field sobriety tests – the horizontal gaze nystagmus test, the walk and turn test, and the one-leg stand test. These three tests have specific instructions and objective scoring systems. However, the results can still be challenged by an experienced Texas DUI / DWI trial attorney.

Despite the availability of standardized field sobriety tests, many police officers rely on non-NHTSA-standardized tests. They include the Rhomberg balance test, the hand-pat test, the finger-to-nose test, reciting the alphabet, and the finger-tap test. These tests are so unreliable that the NHTSA has not endorsed their use.

A Texas prosecutor must prove just one element of a DUI / DWI case in order to obtain a conviction – either that the driver was too impaired by drugs or alcohol to safely operate a motor vehicle, or that he or she violated the state’s “per se” law by having a blood alcohol content (BAC) of .08 percent or greater.

Field sobriety test results are intended to prove the first element of a Texas DUI / DWI charge – that the driver was too impaired to safely operate a motor vehicle. Driving under the influence charges hinge on circumstantial evidence of the state of the driver’s physical or mental faculties after consuming alcohol or other drugs. Although field sobriety tests are strictly optional, police rarely tell drivers that they have a choice.

Mental and physical impairment is at the heart of every Texas driving while intoxicated prosecution. But field sobriety tests are often flawed, because their reliance on physical agility means that a driver can “fail” for reasons that have nothing to do with alcohol intoxication.

This is important because of the way that alcohol affects the human body. Experts agree that alcohol causes both mental and physical impairment, but, mental impairment always takes place before physical impairment occurs. Mental impairment caused by alcohol impairment cannot be disguised. Therefore, if the driver showed signs of physical impairment but no mental impairment, any physical problems must have been caused by something other than alcohol.

Many different conditions, such as injury or illness, can cause physical impairment. Field sobriety tests can be impossible for certain drivers to perform. Nervousness or fatigue can also hinder a driver’s ability to perform.

Field sobriety tests are extremely subjective, and many conditions unrelated to alcohol impairment can cause the accused drunk driver to “fail.” An experienced Texas DUI / DWI defense attorney will thoroughly evaluate the accused motorist’s performance on a field sobriety test to determine the best defense strategy to fight a charge of driving while intoxicated.