Unless a driver approaches a DUI checkpoint, usually an officer needs to have reasonable suspicion that a driver has ingested too much alcohol to instigate a traffic stop and give the driver a field sobriety test. The officer should perceive a problem with the driver that would motivate the officer to pull the driver over in the first place. A lack of reasonable suspicion may prove detrimental to a DUI case.
Without reasonable suspicion, a person arrested for DUI might assert that the officer violated his or her constitutional rights. If a judge agrees, the judge may throw out the arrest or a conviction by a lower court resulting from the arrest. FindLaw provides an overview of what police officers look for when they watch for someone driving under the influence.
Establishing reasonable suspicion
Just about any sign of erratic driving may tip an officer off that something is wrong. An inebriated driver might almost collide with another vehicle while driving. An impaired driver may take actions for no discernible reason, like stopping in the center of the road when a stop is not warranted.
Some impaired drivers exhibit much smaller signs of trouble. They drift in and out of their lanes. They drive slower than the usual flow of traffic. They brake their vehicles more often. Disregarding traffic laws like running a stop sign or making an illegal turn can also indicate a problem.
Lack of reasonable suspicion
If an officer does not witness any of the aforementioned signs or otherwise has no good reason to pull a person over, it can endanger the foundation of a DUI arrest if the officer makes one. Earlier this year, Pennlive reported that a state superior court panel in Pennsylvania ruled than an officer had no reasonable suspicion to pull over a young woman and arrest her for DUI. According to the story, the officer observed that the driver was not exhibiting any signs of driving under the influence and that the vehicle did not show any signs of distress.
While the DUI arrest resulted in a conviction and jail time, the superior court ruled that the officer had no reason to suspect the woman was driving under the influence. The court returned the case to a lower court for a likely acquittal. This story helps illustrate that police officers cannot simply pull over someone on a hunch and need concrete justification before they can make a traffic stop.