Police officers in Pennsylvania are trained to be on the lookout for drivers who appear to be intoxicated. Through observation, they make note a driver's inability to stay in their lane or other allegedly erratic driving habits, and through those observations, they may develop a suspicion of the driver's impairment. Once a driver is stopped an officer may ask a driver to submit to field sobriety testing to confirm their suspicion of drunk driving.
There are several field sobriety tests that officers may use to evaluate drivers' conditions. The first is the horizontal gaze nystagmus. In this test, an officer will ask a person to focus their gaze to the side. If the officer sees involuntary eye movement as the individual undertakes the test, then this may be taken as a sign of intoxication.
Second, a police officer may ask a driver to perform the walk and turn test. This test is what it sounds like: a driver walks by placing one foot in front of the other, and then turns and walks back in the same manner. If the driver cannot do this without stumbling or losing their balance, that loss of coordination may be evidence of alleged intoxication.
Finally, a law enforcement official may require a driver to do the one leg test. This is a balance test that requires an individual to lift one foot off of the ground and stand still. Wobbling or falling may be seen as a sign of alcohol impairment.
Through filed sobriety testing an officer may gain evidence of intoxication and make a drunk driving arrest. However, mistakes can be made during the performance of these subjective tests and individuals who want to challenge the bases of their field sobriety test may wish to consult with criminal defense attorneys.