"We're on Day Two of what's going to be a pretty significant traffic event for the Northeast region," state Transportation Secretary Shailen Bhatt said Tuesday.
"We're basically letting from Florida to Maine know that this issue is going on in Delaware so that trucking interests can be made aware," Bhatt said. "You can't take 90,000 vehicles and just shift them onto 95 and not expect to have an impact."
Southbound traffic from Pennsylvania on I-95 was backed up seven miles Tuesday morning, pushing stalled traffic north of the I-476 connection and snarling traffic on I-476 as well.
Highway messages posted by the Pennsylvania Department of Transportation warned motorists of the Delaware closure, said PennDot spokesman Charles Metzger.
"During a major closure like this, it might take motorists a few days to figure out alternate routes," Metzger said.
Southbound traffic is being diverted to I-95 at the Pennsylvania state line, with a lane open to local traffic through 12th Street in Wilmington. Northbound traffic must exit I-495 at Terminal Avenue.
Officials said the four columns on the south bank of the river are tilted as much as 4 percent from vertical. The bridge will be closed until officials can determine what caused the tilt and what must be done to address it.
Workers placed sensors on the four columns Monday to help engineers determine whether they are still shifting. Crews have excavated around some columns and were checking the soil beneath the columns.
"The whole bridge will be reinspected," said Rob McCleary, chief engineer for the Delaware Department of Transportation.
Delaware transportation officials said the agency got a report late Friday from an engineering firm working on an unrelated project about a possible bridge problem and dispatched an inspection team Monday morning.
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.
The tilting columns support a different part of the 38-span bridge.
Built in 1974, the bridge is scheduled for inspection every two years and was last examined in October 2012.
This article contains information from the Associated Press.