Pennsylvania State Superior Court recently ruled that it takes more than a hunch by the police officer to justify a traffic stop. In this case the stop led to a drunk driving conviction followed by prison.
The United States Supreme Court has agreed to decided three cases where people were suspected of drunk driving. The suspects' contention is that the they're Constitutional Rights were violated.
If a person is stopped for driving under the influence of alcohol or drugs, one of the tests commonly given by police is called the horizontal gaze nystagmus. The flashing hazard lights on the police car or police car headlights can cause optokinetic nystagmus that the arresting officer will misdiagnose as horizontal gaze nystagmus.