The Delaware River Bridge was not one inspectors thought they had to worry about.
The steel-truss bridge was in fact undergoing a $61 million upgrade. Evaluated in 2014 on its three key components -- deck, substructure, and superstructure -- the 60-year-old bridge got passing marks in all three.
Yet last week a worker on a painting crew happened to spot, by chance, something so alarming, authorities rushed to close the bridge to the 42,000 cars that cross it each day: a beam beneath the bridge's deck split in two.
"It was absolutely amazing to see a crack like this," said Henry Berman, chief PennDot engineer for the district.
The 1.2-mile bridge remains closed and, if inspected today, would be labeled "structurally deficient," a designation that describes nearly one in five bridges in Pennsylvania, the second-worst ranking in the country.
What caused the crack in the bridge joining the Pennsylvania and New Jersey Turnpikes and how it can be fixed remain open questions. The bridge has been closed to traffic indefinitely.
The sudden, unexpected fracture led PennDot to schedule new inspections on similar bridges as a precaution, state officials said. The bridge in our region closest in structure to the compromised span is the steel double-decker cantilever Girard Point Bridge, built in 1973 and last inspected in August 2015.
By now, the photo of the fractured truss shared by the Pennsylvania Turnpike Commission likely has been seen on the computer screens of nearly every bridge engineer in the country, said Joseph Yost, a Villanova University civil- engineering professor. Experts have identified within the seam evidence of plug welds, a method used at the time the bridge was built to fill excess holes in a steel beam. The welds can create weak points in the beam. While officials have not concluded what caused the fracture, they have not disputed experts' statements that plug welds were a factor.
The crack should prompt caution, engineers in the region said. But they emphasized that welds leading to failure in one beam likely does not indicate an endemic flaw hidden within the state's bridges.
"I think we would have, before now, seen a lot of instances of this," said Michael Chajes, professor of engineering at University of Delaware. "It tells me that while this may have occasionally happened, it's not a problem that will all of a sudden surface and become an epidemic of bridge fractures."
Even so, experts say inspections need to take place. "If in your structural systems you do have discontinuities and holes that were filled like this, then yes, you may want to investigate under more scrutiny the condition of those structures in the vicinity of those holes," Yost said.
If discovered, the likely solution would be to remove the plug and replace it with a bolt, PennDot officials said.
The welds alone likely didn't cause the beam to break, though, experts said. The break, rust-free, showing no signs of metal twisting or straining, likely happened quickly and recently, perhaps within the last month. Cold weather would have made the steel brittle, and an unusually heavy load on the outer westbound side of the bridge could have pushed the already compromised beam beyond its tolerances.
Such a sudden weight could have come from truck traffic, experts said, but the bridge has also been undergoing significant repairs. Inspectors plan to review permits that should have been issued to any vehicles with heavy loads crossing the bridge, said Carl DeFebo Jr., the turnpike commission spokesman.
Officials also stated the Delaware River Bridge and others like it were overdesigned, with redundancy built into it that ensures the bridge wouldn't collapse with the loss of a load-bearing beam.
Pennsylvania has become infamous for its troubled bridges. It once had the most "structurally deficient" bridges of any state in the country. The "structurally deficient" label doesn't mean a bridge is in imminent danger of collapse, but that at least one of its three primary components, the deck, superstructure, and substructure, had seriously deteriorated. A more rigorous inspection schedule, once a year or once every six months, is a typical result, but problems can be significant enough to require weight restrictions on a bridge, or a closure.
Of the state's 31,893 state and locally owned bridges, 5,573 are rated "structurally deficient." In Philadelphia and its four neighboring counties, 741 out of 3,600 bridges are rated "structurally deficient."
Of the most heavily traveled bridges in the region, 30 are poorly rated as well as "structurally deficient," according to an Inquirer analysis of state data. This number is nearly half what it was 10 years ago.
Since Act 89, a major state transportation funding bill, passed in 2013, Pennsylvania has devoted $1 billion more to the statewide construction budget.
Brad Rudolph, a PennDot spokesman, said five of those 30 are scheduled for construction in 2017, part of a plan to upgrade scores of "structurally deficient" bridges across the state.
The sudden crack in the Delaware River Bridge isn't evidence that bridge inspections are insufficient, experts said.
"Bridges don't change very rapidly," Chajes said, noting fractures like the one in the Delaware River Bridge are rare and, "can really occur from a very undistinguishable crack to a brittle fracture that happens all at once. It probably was totally undetectable to the human eye."