Transportation officials ordered a “safety stand down” and suspended for the weekend a 91 freeway widening project after a new highway section being lowered into place over a Corona street suddenly dropped more than a foot, hitting wooden support beams that struck workers.

Nine workers beneath the bridge deck were injured, three of them critically, in the 11 p.m. Friday accident. Eight remained hospitalized Saturday. Oct. 10, the Riverside County Transportation Commission said.

The 91 remained open to traffic, but the surface street at the location of the incident, East Grand Boulevard, will remain closed until early Monday as the investigation continues.

UPDATE: Road beneath partially collapsed bridge deemed safe to reopen Monday

“Any time there is a serious accident involving injuries on a construction site it is imperative to stop, re-examine and re-emphasize the overall safety procedures on the project,” Riverside County Transportation Commission Executive Director Anne Mayer said Saturday in announcing the temporary work halt.

The accident happened when workers were lowering a new section of the widened highway into place on the eastbound lanes, officials said.

Something went wrong with the jacking operation and caused the bridge deck to drop about 16 inches. The bridge deck struck wooden support beams, which hit the workers.

“The bridge is seated in the proper position and inspections of the bridge have been made by the project structural engineering team,” said Eliza Echevarria, spokeswoman for the transportation commission.

RELATED: 91 freeway projects have seen trouble before

Corona resident Louis Marroquon, who lives in the 800 block of Quarry Street, said he was at home Friday night when he heard a loud noise.

“It sounded like thunder,” Marroquon said. “It was a big sound.”

Having worked in construction, Marroquon had a feeling that the crash had something to do with the project on East Grand Boulevard. Soon after the accident, he heard sirens and went outside to check it out. That’s when he heard crying, he said.

“It was a big deal going on,” Marroquon said.

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All the injured workers are affiliated with the Atkinson Walsh Construction Joint Venture, according to the Riverside County Transportation Commission.

Atkinson Walsh project manager Jan Bohn said throughout the company’s work on the 91 project, safety has always been a priority. Bohn said the team was devastated by Friday’s accident.

“Everyone goes home every day, that’s a big deal to us,” Bohn said Saturday. “We failed yesterday.”

Investigators from Atkinson Walsh, the transportation commission and the California Occupational Safety and Health Administration were on the scene investigating the accident, Bohn said.

Mayer said that Atkinson Walsh will hire a forensic engineer who is not associated with the project to evaluate what happened.

The Clayton, Mo., company’s listing on the California State Licensing Board website did not have a link Saturday for a public complaint disclosures, which the website stated would only appear if there were any to report. The site cautioned that it may not be up to date due to workload.

The $1.4 billion widening project began in July 2014, and is one of two major projects along the 91 in Riverside County. It will extend two tolled express lanes in both directions on the 91, from the border of Orange and Riverside counties east to the I-15/91 interchange in Corona.

It will also add one regular lane in both directions from the I-15/91 interchange east to Pierce Street in Riverside, and improve five local interchanges, as well as the I-15/91 interchange.

It is scheduled for completion in 2017.

It is separate from another 91 freeway widening project through Riverside that begins about five miles east of Pierce Street. Work on that project is not affected by Saturday’s suspension order, transportation commission spokeswoman Echevarria said.

That $248 million project will add high-occupancy vehicle lanes in both directions between Adams Street in Riverside and the interchange 60/91/215 interchange downtown. Started in March 2012, it is slated for completion this December.