Witnesses say the collapse of a bridge in Washington state last night occurred after an oversized truck struck the metal arches that cover traffic crossing the bridge. There were no fatalities or serious injuries, although three people were rescued after their vehicles plunged into the Skagit River. They were taken to area hospitals.

Authorities are scrambling to set up ways to divert traffic away from that section of the I-5 freeway, which usually carries 71,000 vehicles a day. Traffic was backed up in both directions overnight and long delays are expected over the Memorial Day Weekend. The collapsed occurred between Mt. Vernon and Burlington.

“Somewhat better than minimum adequacy”

The 1,112-foot steel truss bridge on I-5, the main freeway that runs up and down the West Coast between the Canadian and Mexican borders, was built in 1955. A 2010 inspection of it by the state’s Department of Transportation judged it to be “somewhat better than minimum adequacy.” The bridge was also inspected in 2008 and 2006.

Washington Governor Jay Inslee said an investigation has been launched into the incident. Plans are already being developed to build a replacement span.

The National Transportation Safety Board (NTSB) has launched a go-team to the site to conduct its own investigation.

America's aging bridges

According to a report by the American Society of Civil Engineers (ASCE) one out of nine of U.S. bridges are rated structurally deficient, while the average age of the nation’s 607,000+ bridges is 42 years old.

“The Federal Highway Administration (FHWA) estimates that to eliminate the nation’s bridge deficient backlog by 2028, we would need to invest $20.5 billion annually, while only $12.8 billion is being spent currently,” says the ASCE. “The challenge for federal, state, and local governments is to increase bridge investments by $8 billion annually to address the identified $76 billion in needs for deficient bridges across the United States.