Federal regulators are about to announce what they believe caused a bridge to collapse in Pittsburgh more than two years ago, sending vehicles plummeting into a ravine and injuring several people. The 447-foot-long (136-meter) bridge's collapse dropped a bus and four cars about 100 feet (30 meters) on the day President Joe Biden visited Pittsburgh to promote spending on infrastructure. Another vehicle drove off the east bridge abutment and landed on its roof.