Updated 5/12/2011 at 9:30 p.m.

HAMMOND, Ind. (CBS/WBBM) — Police in northwest Indiana are looking for the person or people who threw rocks onto vehicles overnight from Cline Avenue.

As WBBM Newsradio 780’s Bernie Tafoya reports, Indiana State Police say 15 vehicles were damaged by the rocks, which were thrown onto the Interstate 80 entrance ramp near Hammond, Ind.

LISTEN: Newsradio 780’s Bernie Tafoya reports

State police and Lake County, Ind., sheriff’s deputies were called to I-80 at Cline Avenue around 3:45 a.m.

The rocks were thrown from the top of the southbound Cline Avenue ramp to westbound I-80.

Fifteen vehicles — including two passenger cars, one garbage truck, and four semi trucks — sustained body damage or broken windshields, state police said.

“I thought it was gunfire,” driver Donna Schmiedl said.

She and several drivers spent the day replacing shattered windshields.

Only seven motorists wanted to file police reports.

Police have not caught the rock throwers, but promise they will, and that they could face jail time.

The Sun-Times Media Wire contributed to this report.