A police officer must have reasonable suspicion that a driver is impaired before pulling him or her over by personally witnessing the driver driving erratically in some way. If there is reasonable suspicion to pull over a driver, then there must be probable cause for an arrest. This means that before making a DUI arrest, the police officer must have probable cause to believe the driver is driving under the influence or sufficient evidence that the driver has “probably” committed the crime of DUI.
Officers usually get this probable cause by asking the driver questions to see if his or her words are slurred, eyes red and watery, or if there is a strong smell of alcohol coming from the driver. If questioning the driver leads the officer to believe he or she is intoxicated, the officer may ask the driver to perform field sobriety tests to be sure before an arrest is made. While field sobriety tests are used in every state – but are not mandatory in any state – they are often less than accurate yet can be used as evidence in court to prove an individual was driving under the influence.