A series of shootings over nearly two weeks along highways in the Phoenix area, most involving the same stretch of Interstate 10, has alarmed residents and confounded the police.

The authorities reported another shooting early Thursday involving a tractor-trailer pierced through the side by a bullet, bringing the total number of incidents to 11 since Aug. 29. Eight of those involved bullets, and three involved “projectiles,” officials said.

Only one minor injury has been reported: A 13-year-old girl was cut when a bullet shattered a window of the car she was in.