As a means of identifying possible drivers who are under the influence of drugs or alcohol, law enforcement officials perform roadside field sobriety tests. If an officer pulls over a driver and suspects that he or she is under the influence of alcohol, the officer has the right to request that the driver take a field sobriety test, breathalyzer test, blood test, or urine test.
A driver is required by law to submit to all of these tests, except the field tests because they are considered to be voluntary. However, if a driver chooses to take a field test and performs poorly, the officer now has probable cause to arrest him or her for suspicion of driving under the influence.
In 1982, the National Highway Traffic and Safety Administration (NHTSA) established three official tests for officers to use to determine a driver’s intoxication level. To ensure the reliability and accuracy of the tests, the officers are trained by the NHTSA before administering the tests. This also ensures that the test results are consistent.
Most of the field sobriety tests examine a driver’s coordination, balance, and dexterity, all of which are affected when a person’s blood alcohol content level increases. Many of the tests also help an officer to determine if a person is able to perform simple tasks simultaneously, since alcohol impairment diminishes the ability to divide his or her attention amongst multiple tasks.
There are many different types of field tests that an officer can request a person to take. However, there are only three standard tests established by the NHTSA. These three tests include walking in a straight line and turning around, standing on one leg while counting, and the horizontal gaze nystagmus.
In this last test, an officer positions an object, usually a pen, about one foot from the driver’s face and then moves it from one side to another while observing the driver’s eye movements. If there is any involuntary jerking or trembling of the eyes, the driver most likely has been drinking.
In the other two tests, the officer examines the person to see if he or she is able to remain balanced and follow instructions. Usually, if a person has been drinking, he or she leaves space between heel and toe, has trouble taking steps in a straight line, or loses balance during the test.
The non-standard tests are similar to the three official tests and examine relatively the same abilities. Sometimes, an officer may ask a driver to place his or her feet together while standing with eyes closed and arms extended, and then to bring the index finger to the nose.
In order to make sure that the test results hold up in court, officers must administer the tests in adequate lighting and on level, dry ground. If weather conditions prohibit this, the officer only administers the horizontal gaze nystagmus test.
Another factor that must be taken into account is that elderly and overweight people often have difficulty with these tests when sober, making it difficult to determine for certain if they have been drinking. Under these circumstances, officers usually back up the field tests with a breathalyzer test.