All four shootings happened on a short stretch of I-10 in Central and West Phoenix.
The vehicles were shot multiple times and some drivers did not realize what happened until after the shooting. Others had their windows shot out.
DPS released photos showing bullets through the windshield and passenger windows. One of the targets was a tour bus, and a bullet went through one of the seats.
Troopers say these are drive-by shootings, they believe the gunman is driving on the interstate alongside the victims and opening fire.
Investigators are asking the public to be aware, and to give them a call if they see anything suspicious.
"You should be concerned, because we have someone or som people shooting guns at moving cars on Interstate 10. It has not ended in tragedy but it could... it doesn't matter what you think you saw or what may seem odd. If it causes you pause and you think you may have seen something please call us and let us be the ones to determine if whether what you saw id valid or of concern or not," said DPS Col. Frank Milstead.
Anyone with information is asked to call DPS at 602-223-2000.