So far, two people have suffered minor injuries in the incidents.
Police said the incidents have happened between the South Alston Avenue bridge and Briggs Avenue. They say some items have been thrown from overpasses or bridges and others from embankments beside the road.
The incidents have usually occurred at night and most of the vehicles have been in the northbound lanes. The objects thrown have usually been rocks or bricks.
The latest incident happened around 6:30 p.m. Tuesday just outside of Alston Avenue.
According to police reports, the driver and passenger in that incident weren't hurt, but the car suffered about $500 worth of damage.
Anyone with information is asked to call police at (919) 560-4415, ext. 29311 or CrimeStoppers at (919) 683-1200.