At every traffic stop, police officers are trained to look for signs that a driver is under the influence of drugs or alcohol. In Maryland, police will use a variety of exams at the initial traffic stop to determine a driver’s sobriety. These tests include the one leg stand test, Horizontal Gaze Nystagmus, and the “walk and turn” test. A preliminary breath test may also be administered after the initial stop and an official breathalyzer test will be conducted at the police station upon arrest.

1.) Walk and Turn - The Walk and Turn test requires that the suspect walk a straight line, turn, and walk the line in reverse. Failure can be any kind of deviation from the proscribed path, as well as clumsiness when turning. Maintenance of a straight line while intoxicated can be difficult due to physiological changes made to the central nervous system while under the influence of alcohol. This test is one which measures balance and coordination. Here are the indicators that officers use to judge that a driver is intoxicated.

• Subject used arms for balance.
• Subject cannot maintain balance during instructions.
• Subject does not take the proper number of steps.
• Subject steps off the line.
• Subject stops to regain balance.
• Subject fails to walk heel-to-toe.
• Subject begins to walk before the instructions are completed.

2.) The One Leg Stand requires that the suspect stand on one leg to prove coordination and balance. Difficulty balancing is taken as a sign of intoxication. These indicators are what the police look for to judge intoxication.

• Subject used his arms to balance.
• Subject swayed to regain his balance.
• Subject hopped to regain his balance.
• Subject rested the raised foot down early.

3.) Horizontal Gaze Nystagmus - This test is done by an officer moving a flashlight or finger in front of a driver’s eyes. First the officer is trained to look for uneven pupil size, which is a sign of injury. The officer then is checking to see that eye movement is even, and not jerking. When eye tracking is erratic at the maximum amount of deviation from the object, an officer can say that this is symptomatic of a BAC in excess of 0.10, above the Maryland limit. This test is often viewed as very controversial, since merely completing the test successfully, even when failing, shows that the suspect has good control over their faculties. This test, along with the One Leg Stand and Walk and Turn can be used in conjunction with each other to determine probable cause, or a high probability that the driver is intoxicated. The officer is trained to look for these signs when conducting an HGN test.

• Subject’s eyes cannot smoothly track the pen.
• Subject demonstrates a sustained and distinct nystagmus at maximum deviation, or approximately 60 degrees from the center.
• Subject’s nystagmus begins before the eyes turn 45 degrees from the center.

Failure of one of these tests usually results in the officer’s application of a breathalyzer to determine an individual’s sobriety. It is important to note that these tests are supposed to be used within very strict guidelines, and that many officers are not experts in conducting these tests.