However, investigators said they are having trouble tracking down a suspect because victims are not giving a consistent description.
"It's scary because I drive on the 15 every single day," said Claudia Acevedo of Norco.
The freeways that have been affected include the 15 between the 138 and Sierra, the 10 through Riverside and San Bernardino counties and the 215 through Colton.
Authorities believe the suspect or suspects may be shooting with a pellet gun or a BB gun, but they aren't sure yet because they haven't recovered any projectiles from the vehicles that were hit.
"I was driving north, 15 Freeway, toward Hesperia, and then I hear the noise, back of my window explodes," said victim Robert Gomez.
There have been 30 similar incidents in the last few weeks, but so far, no one has seen any suspects.
The CHP urges drivers to report anything that looks suspicious. Anyone with information is urged to call authorities at (909) 383-4247.