In certain instances, Arizona law authorizes a police officer to first stop a driver for a traffic violation and then use that stop for further investigation of DUI. In addition, a stop can still be considered legal if a police officer develops probable cause for DUI even though the police officer might have originally pulled the driver over for another reason. This type of stop can sometimes be referred to as a “pretextual stop".
Furthermore, a police officer can also legally stop an individual for one reason and then arrest that individual for another reason only if the initial reason for the stop is valid and not made up. For example, a police officer can stop a driver in Phoenix, AZ if their license plate is expired. Should the officer then develop probable cause to arrest the driver for DUI, the arrest can be considered legal depending on the circumstances involved in the case.