FOG BLOG U.S. NEWS LOG: PITTSBURGH BRIDGE COLLAPSE, BUS FALLS INTO RAVINE NTSB INVESTIGATING:

Pittsburgh bridge collapses, drops city bus into ravine...PITTSBURGH -- A 50-year-old bridge collapsed in Pittsburgh early Friday, requiring rescuers to rappel down a ravine and form a human chain to reach a few occupants of a municipal bus that plummeted along with the span. No deaths were reported.

The collapse came hours before U.S. President Joe Biden arrived in the city to promote his $1 trillion infrastructure law, which has earmarked about $1.6 billion for Pennsylvania bridge maintenance.

At least four people required hospital treatment. Five other vehicles were also on the bridge at the time. The cause was being investigated, and crews searched under the debris for additional victims.......A large crack showed on the end of the bridge where the segmented bus landed 150 feet (46 meters) down in the ravine, as if hit by an earthquake. A car landed upside down in front of the bus, which was operated by the Pittsburgh area's transit agency.

The Forbes Avenue bridge over Fern Hollow Creek in Frick Park came down at 6:39 a.m., city officials said. The loud noise from the collapse was followed by a hissing sound and the smell of natural gas, witnesses said.

"The first sound was much more intense, and kind of a rumbling, which I guess was the structure, the deck hitting the ground," said Ken Doyno, a resident who lives four houses away. "I mean, the whole house rattled at that point."

Ruptured gas lines along the bridge produced the leak, and the supply of gas was shut off within a half-hour, city officials said.

As Biden toured the scene, an officer told him a person who was running by helped first responders get people out of cars. He called it a miracle.

"It really is, it's astounding," Biden said.

By midafternoon, three adults were being treated, and all were in fair condition, the UPMC hospital system said. A fourth person had received treatment and was released.

The National Transportation Safety Board sent a team to investigate. The agency tweeted a photo late Friday of Chair Jennifer Homendy at the scene.

A search-and-rescue team combed the area, said Sam Wasserman, a spokesperson for Pittsburgh Mayor Ed Gainey. Drones were brought in to help.

Most of the 10 people evaluated for injuries were first responders who were checked for exhaustion or because of the cold and snowy weather, Gainey said.

The segmented bus operated by the Port Authority of Allegheny County had two passengers in addition to the driver, said Adam Brandolph, spokesperson for the agency.

The bus driver, Daryl Luciani, told WPXI-TV that as soon as he reached the bridge, he believed it was collapsing.

"I could just feel it," Luciani told the station. "The bus was bouncing and shaking and it seems long, but it was probably less than a minute that the bus finally came to a stop, and I was just thankful that nobody on the bus was hurt."

The passengers appeared to be OK, he said, so he pulled the air brake and waited for help to arrive. First responders reached them after descending with flashlights in the predawn darkness and used a rope to help him and other occupants get to safety, Luciani said.