Falling chunks of concrete brought traffic to a standstill in both directions of the Richmond-San Rafael Bridge on Thursday morning. Westbound lanes were opened at about 7:20 p.m., according to a CHP tweet.

Debris ranging in size from a “football to golf ball” fell from the upper deck of the bridge onto the lower deck, which struck at least one vehicle around 10:30 a.m., according to CHP.

“Caltrans and CHP, in an abundance of caution, closed the bridge this morning to do a safety inspection,” Caltrans spokesperson Vince Jacala said. “We understand it’s a busy time in the Bay Area, but our main concern is the safety of the traveling public.”

Authorities decided to close all lanes down completely just before noon while Caltrans workers inspected the structure. Caltrans District 4 estimated the bridge would re-open by 6 p.m., but according to 511 SF Bay, all lanes have been shut down twice since Caltrans inspectors arrived.

“We don’t know the exact cause of what’s happening to it,” Jacala said. “If we need to close it again because of safety, we’ll have to close it again.”

All vehicles that remained on the bridge prior to its first closure were escorted to safety by 1 p.m., according to CHP.

In a Facebook update posted by the CHP office in Marin, Caltrans District 4 engineers said they could re-open one lane in each direction while conducting repairs by 3 p.m., but this attempt proved unsuccessful as the traffic caused more concrete pieces to fall.

With heavy delays near both sides of the Richmond-San Rafael Bridge, drivers had to rely on the Golden Gate and Bay bridges, Highway 37 and Interstate 80. Caltrans urged Bay Area residents to avoid the bridge until further notice.