If law enforcement pulls you over for driving erratically in Missouri, they may request that you step out of the vehicle and perform field sobriety tests. While these standardized tests are not mandatory, officers may arrest you for driving while intoxicated.
FieldSobrietyTests.org reports that while DUI laws may vary from state to state, police officers around the country administer the same field sobriety tests when they suspect drivers are under the influence of alcohol. The tests help law enforcement estimate your blood alcohol content. This establishes probable cause for an arrest. Police must provide instruction and demonstrate the walk and turn test, the one-leg stand tests before requesting you do the same. This is part of the National Highway Traffic Safety Administration protocols.
During the walk and turn test, you must take nine heel-to-toe steps forward in a straight line, then turn and repeat the process back, focusing on your feet, with arms at your sides. You fail the test if you take the wrong number of steps or step off the “line.”
For the one-leg stand, the officer requests that you raise one leg six inches, your foot parallel with the ground and hands out to the sides. You must count, focusing on your foot until the officer asks that you stop. Swinging your arms, putting your foot down or swaying indicates impairment.
The officer administering the horizontal nystagmus test looks for uneven pupil size and equal tracking in your eyes when following an object left to right. There are six clues that he or she looks for when giving this test. If they observe at least three of these indicators, they may arrest you for drunk driving.