Delaware officials on Monday ordered the emergency closure of the Interstate 495 bridge over the Christina River in Wilmington after discovering that four support columns are tilting.
The closure is expected to last through the day Tuesday's morning commute meaning drivers should expect delays along I-95, the alternate route.
The 4,800-foot bridge normally carries about 90,000 vehicles a day on I-495, which diverts traffic around the city of Wilmington and toward the Port of Wilmington. The route parallels Interstate 95, which runs through downtown Wilmington.
"We understand that there will be a significant impact to the traveling public," said state Transportation Secretary Shailen Bhatt.
He added that he doesn't know how long the bridge will be closed. "It could be significant amount of time," he said.
Officials said the four columns on the south bank of the river are tilted by as much as 2.4 degrees, or 4 percent, from vertical. The bridge will be closed in both directions until officials can determine what caused the shifting of the columns and what needs to be done to address it.
"The whole bridge will be re-inspected," said Rob McCleary, chief engineer for the Delaware Department of Transportation.
Delaware transportation officials said the agency received a report late Friday from an engineering firm working on an unrelated project about a possible problem with the bridge. The department sent out an inspection team Monday morning.
"It didn't come to us as like an emergency call," Bhatt said, explaining why a team wasn't sent earlier.
Officials closed I-495 northbound at Terminal Avenue, which leads to the port, and that local northbound traffic can stay on I-495 to Terminal Avenue. Southbound traffic on I-495 was diverted at the Pennsylvania state line, with traffic diverted onto I-95 southbound. Southbound port traffic is being directed to Interstate 295 east and then to Delaware 9 north to the port.
Officials said the main span of the bridge over the water is considered "fracture critical," meaning that failure of one element could result in failure of the entire bridge, which consists of a concrete deck on steel beams supported by 37 reinforced concrete columns. However, the tilting columns in question support a different area of the 38-span bridge.
"The main span is not what's in question here," McCleary said.
The bridge was built in 1974 and is scheduled to be inspected every two years. It was last inspected in October 2012.
But officials noted that the tilting of the columns has resulted in the shifting of concrete pier caps resting on top of them. That shifting, in turn, has led to a height difference of about a foot between a northbound barrier wall on the bridge deck and the adjacent wall on the southbound side, according to McCleary.