Nearly 60 heavily traveled bridges in the Philadelphia region are in disrepair and rated as bad as, or worse than, the condition of the Minnesota bridge that collapsed Aug. 1, according to state and federal data.

Deteriorating because of age, rust and crumbling concrete, the 57 "structurally deficient" bridges are vital links on Interstate 95, the Schuylkill Expressway, the Pennsylvania Turnpike, U.S. 130 and other highways. Each bridge carries at least 25,000 vehicles a day; some carry more than 160,000 a day.

Officials in Pennsylvania and New Jersey say the bridges remain safe. But they acknowledge that officials in Minnesota believed that, too, before the I-35W bridge tumbled into the Mississippi, carrying 13 people to their deaths.

"We think we have a robust inspection program and are prudent in our judgments," said Charles H. Davies, the engineer who is the Pennsylvania Department of Transportation's assistant district executive for the Philadelphia district. "But resources are limited, and we have to make judgments as best we can."

Most of the deficient bridges, some a century old, are scheduled to be replaced or rebuilt by 2012. Pennsylvania's legislature last month approved a $532-million-a-year increase in bridge and highway funding, prompted by the record number of troubled bridges in the state.

Even with the new money, the backlog of bad bridges is so large that fixing or replacing them all will take decades. Pennsylvania has the most structurally deficient bridges in the nation, nearly 6,000.

And that tally is likely to rise as the many bridges built in the highway boom of the late 1950s and 1960s reach the end of their expected lives.

For drivers in the Philadelphia region, the horrifying images from the Minnesota collapse raise a frightening question every time they cross a bridge: Could it happen here?

Engineers try to answer that emotional question with dry equations; they reduce the ravages of time and weather and stress to numbers. But in the end, it's an inexact science.

"It's a reminder of how difficult it is to know everything," Davies said. "We have to have tremendous respect for what we don't know."

By the numbers, the Minnesota bridge didn't seem especially vulnerable. It was considered "structurally deficient," meaning it had serious deterioration in at least one of its three primary components: the deck, the superstructure or the substructure. But it was not considered in imminent danger of failing.

Inspectors give each bridge a "sufficiency rating" on a 0-to-100 scale, using a formula that evaluates safety, serviceability, and how essential the bridge is. And they assign a condition rating for each of its three primary components on a 0-to-9 scale, from "failed" (0) to "excellent" (9).

The Minnesota bridge had a sufficiency rating of 50, with a deck score of 5 ("fair"), a superstructure score of 4 ("poor), and a substructure rating of 6 ("satisfactory"). The low superstructure rating made it a "structurally deficient" bridge. Investigators are still uncertain what caused the collapse.

In the eight-county Philadelphia region, 57 bridges that carry at least 25,000 vehicles daily have ratings at least as low as the Minnesota bridge's.

The worst, by the numbers, is the DeKalb Pike bridge in Bridgeport. Built in 1928, the bridge gets a sufficiency rating of 3 out of 100. The substructure is rated 2 ("critical"), and the superstructure and deck are each rated 4 ("poor").

Large chunks of concrete have fallen from the massive structure, which carries U.S. 202 over the Norfolk Southern railroad tracks, but the bridge remains open without weight limitations.

"It's bad, but it's safe," Davies said. "It's so well built that it didn't need to be weight-restricted."

Construction bids to replace the bridge are to be let this year, according to PennDot.

I-95 has more deficient bridges than any other highway in the region: 15. The Pennsylvania Turnpike has seven and the Schuylkill Expressway one, according to state data.

I-95, the most heavily traveled highway through the region, faces a major rebuilding over the next few years, and all bridges between Cottman Avenue and Vine Street are to be replaced or repaired by 2014. The cost is expected to be significantly above the previously estimated $1 billion, PennDot officials say.

Deficient bridges may be closed or given weight restrictions. In the five Pennsylvania counties in the region, 12 bridges are closed and 63 have weight restrictions because of structural problems.

Of the major Delaware River bridges in the region, only the Burlington-Bristol is "structurally deficient." (The Tacony-Palmyra was rated structurally deficient on a list PennDot released last week, but that did not reflect recent repairs. New data from the New Jersey Department of Transportation have removed the Tacony-Palmyra from the deficient list.)

The Burlington-Bristol Bridge, owned and operated by the Burlington County Bridge Commission, has cracks and flaking concrete throughout, and the supporting abutment on the New Jersey side is deteriorating. In addition, the operating ropes for the drawbridge are in poor condition.

The deteriorating abutment is to be repaired in the spring, and the operating ropes will be replaced later in 2008, said David Lowdermilk, vice president of Pennoni Associates, the firm that conducts annual inspections for the bridge commission.

Two low-ranking bridges not scheduled for repair or replacement are on I-95 in Bristol Township over Neshaminy Creek. The north- and southbound bridges are among the five lowest-scoring bridges in the region, based on sufficiency rating. The substructures are rated in "poor" condition.

Davies said a recent inspection "shows they look like they have a lot of life left," though he acknowledged that "ultimately, they'll have to be on our list."

With nearly 6,000 deficient bridges in Pennsylvania and nearly 750 in New Jersey, and with the aging bridges of the '50s and '60s quickly wearing out, the question, Davies said, has become: "Can we replace them as fast as they will deteriorate?"

For an interactive map, go to http://go.philly.com/bridges

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