I talk to people all the time about DUI's,  whether it be clients, police officers, other Phoenix DUI lawyers, or prosecutors.  And one of the things that comes up quite a bit is the reason for the officer stopping a DUI suspect.  This question is not trivial, and is in fact very important.  

An officer cannot stop random vehicles, regardless of the time of day or location, in the hopes that any random stop will lead to a DUI arrest.  An officer can only stop a driver for one of three reasons: first, a equipment failure; second, a civil traffic violation; and three, reasonable suspicion that a crime has been committed. 

Equipment failure means exactly that: there is something about the car that violates Arizona laws for safe vehicles.  Of course, equipment failure does not necessarily mean the car is unsafe, just unsafe enough for the officer to pull over the driver.  That could be something as little as a tiny crack in the windshield or one of the license plate lights is not operating and visible past 50 feet. It could also be something serious like the car is on fire. 

A civil traffic violation means the driver has violated traffic laws.  It could be something like speeding or expired registration.  It could also be something like not making a turn into the first available lane.  My experience is that not turning into the first available lane will not get you pulled over at 1 PM, but will certainly get you pulled over at 1 AM.

Finally, reasonable suspicion means the officer has reasonable cause to believe that a crime is being committed.  That would mean something like weaving heavily, not moving for a green light, asleep at the wheel etc...   Of course, most officers will cite multiple reasons for pulling over a driver because that way, they could justify the stop on multiple reasons. 

Assuming the officer had valid reasons to pull you over, what should you do?