BEAVER (AP) -- Four bridges in Beaver County reopened Thursday after an apparent bomb threat hoax. The bridges, two each over the Ohio and Beaver rivers, were closed shortly after midnight when someone made a hang-up call to the county 911 center, police said. All were open again by late Thursday morning. Police traced the call to a pay phone, where they found a note saying there was a bomb on one of the bridges. All four spans were closed as a precaution, county emergency officials said. The East Rochester-Monaca Bridge over the Ohio River reopened about 8:15 a.m. Thursday to help ease traffic jams in the area. The Rochester-Monaca Bridge, also over the Ohio River, and the Beaver-Rochester and Bridgewater bridges, both over the Beaver River, had reopened by shortly after 11 a.m., according to the Pennsylvania Department of Transportation. The Rochester-Monaca Bridge along Route 18 carries about 13,000 vehicles a day, and the East Rochester-Monaca Bridge along Route 51 averages nearly 16,000 vehicles, according to PennDOT. The bridges over the Beaver River carry a combined 14,000 vehicles daily. No one has been charged with making the threat. Federal Homeland Security officials were notified.