One rock hit a car leaving a woman in critical condition.
It happened Thursday night on I-80 in Union County.
The woman and her family were travelling from Ohio to New York City.
Pennsylvania State Police say the suspects threw the rocks off a bridge. One of the rocks went through a car's windshield and hit the woman in the passenger seat.
An 18-year-old and a juvenile, who live near the bridge, face aggravated assault charges.
Police say they're looking for two more suspects.