Troopers use several different tests on suspected impaired drivers. They consist of two parts: (1) roadside tests and (2) tests done after the arrest. Roadside tests include the horizontal gaze nystagmus test, the walk and turn test, and the one leg stand test. A preliminary breath test is also used to screen suspected impaired drivers prior to arrest. After an arrest is made, an impaired driver will be asked to submit to a chemical test which will be used to determine his or her blood alcohol content (BAC). For a chemical test, troopers collect breath, blood, and/or urine samples.