Police officers in Louisiana and around the country sometimes ask motorists who they believe to be under the influence of alcohol to take standardized field sobriety tests. These tests were developed by the National Highway Traffic Safety Administration in the 1970s and have been improved to the point where they are now considered to be more than 80% effective at identifying intoxicated drivers, but that figure is highly misleading.
Field sobriety tests are subjective
Police officers who interpret the results of field sobriety tests make subjective judgments, which means their opinions can be influenced by bias even if they are trying to be fair. A police officer who strongly suspects that a motorist is under the influence of alcohol may interpret the results of a test far more harshly than an officer who noticed no signs of intoxication after pulling over a driver for making an erratic lane change, which is why many scientists believe that walk and turn, one-leg stand and horizontal gaze nystagmus tests are not reliable enough to be used as evidence in DUI cases and should not be used by law enforcement to detect alcohol impairment.
Age and medical conditions can influence the results
Field sobriety tests are designed to identify physical signs of alcohol intoxication that can be also be caused by common medical conditions like inner ear infections, and people over the age of 40 could have trouble passing one even while completely sober. When researchers studied field sobriety tests in 2009, they discovered that subjects over the age of 40 performed as poorly as younger subjects with blood alcohol concentrations higher than the .08 legal limit.
Implied consent does not apply
Louisiana’s implied consent law requires motorists to provide breath, blood or urine samples when asked to do so by police officers who have reason to believe they are intoxicated, but it does not require them to submit to field sobriety tests. Police officers often request these tests when they have suspicions but lack probable cause, and drivers should think very carefully about subconscious bias and the complexity of the human body before complying.