Months after Baltimore bridge collapse, how safe are Lehigh Valley’s bridges?

Last week, the Walnut Street Bridge in Slatington was closed abruptly for replacement , a project that will take two to three years, due to deteriorating conditions.

The Pine Street Bridge between Whitehall Township and Catasauqua is rated poor, but remains open to traffic.

A small bridge in the middle of Northampton County, with a rating of fair, also has no restrictions.

What do these bridges have in common? They are among approximately 30 spans in the Lehigh Valley that fit the category of being “fracture-critical.”

Nationwide, millions of drivers pass over a similarly constructed bridge each day, likely without realizing it. These types of bridges — designed without redundancies, so if one key element fails the entire structure could collapse — were commonly built decades ago because they were cheaper.

But the deadly collapse of the Francis Scott Key Bridge in Baltimore in March drew attention to the bridge’s construction, even though ultimately, that was ruled out as a factor.

However, structural issues have been blamed for other bridge collapses, including that of a bridge in Minneapolis along Interstate 35W in 2007. The bridge was also fracture-critical.

Still, experts say there’s little to worry about in the Lehigh Valley.

“The designation shouldn’t lead anybody to being more or less concerned,” said Richard Runyen, PennDOT’s chief bridge engineer, adding that he’d care more about when a bridge is showing signs of deterioration.

What is a fracture-critical bridge?

Runyen explained that in the past, fracture-critical structures like truss bridges, were easier to build than something like a suspension bridge or a cable-stayed bridge. Those latter kinds of bridges are now easier and more cost-effective to build than the former, he added, to the point that he doesn’t expect the Key Bridge’s replacement to be fracture-critical, particularly since it’d help keep support structures out of the water and out of the way of marine traffic.

Some of the heavily used fracture-critical bridges in the Lehigh Valley include the Gene Hartzell Memorial Bridge on Route 33 that spans the Lehigh River; the Hill to Hill and Minsi Trail bridges, both in Bethlehem; and the Cementon Bridge in Whitehall Township, which is in the process of being replaced but remains open to traffic while a new bridge is being built.

Following the March 26 Key Bridge collapse, caused when a massive ship crashed into supports, PennDOT assessed the state’s bridges to see if any action was necessary. They found no causes for concern in the Lehigh Valley.

“We’re satisfied,” Runyen said. “It’s not really the same as Baltimore, so we’re very happy with what we have out there.”

For one thing, he said the Key Bridge’s collapse didn’t have as much to do with it being fracture-critical, as it’s unlikely for any bridge to survive an extreme event like a cargo ship crash.

Engineering experts in various media reports said the design of the Key Bridge was not the reason it collapsed when the massive container ship slammed into one of its main support piers, but it helped explain why the structure gave way within seconds after impact.

“If you knock out any leg of any type of bridge, something’s falling down,” Runyen said.

The Lehigh Valley doesn’t have major high-traffic channels like Baltimore. Pennsylvania has some outliers, such as the Port of Philadelphia and the ship traffic it sees on the Delaware River, but Runyen said that the river’s crossings are farther north, away from the port traffic.

“The [fracture-critical] designation shouldn’t lead anybody to being more or less concerned,” he said, adding that he’d care more about when a bridge is showing signs of deterioration.

‘The systems are quite safe’

David Mante, an associate professor in the Civil and Environmental Engineering Department at Lafayette College, detailed the number of precautions officials take to make sure fracture-critical bridges are safe.

These include inspecting fracture-critical bridges at least every two years, limiting a bridge’s load-carrying capacity when inspectors notice damage, and closing the bridge altogether if the damage is extensive enough.

“While the public certainly may derive comfort from a structurally redundant bridge, there is nothing inherently dangerous about a properly designed and routinely inspected fracture-critical bridge,” he said.

Lehigh University structural engineering professor Richard Sause, who has spent about half of his 35-year career studying bridges, said motorists should feel comfortable traveling over Lehigh Valley spans.

“I don’t think there is any reason [for concern],” said Sause, director of the school’s Advanced Technology for Large Structural Systems (ATLSS) Center. “The probability of being injured in a vehicle accident is much greater than a bridge failure, because the systems are quite safe, and the bridges themselves are safe.”

By “systems,” Sause said he is referring not only to bridges themselves but the processes of inspecting and maintaining spans.

Of the 30 Lehigh Valley bridges considered fracture-critical, PennDOT owns 12. Of those, 11 have a “poor” rating, and 12 have future work scheduled such as rehabilitation, replacement or removal.

A poor rating doesn’t immediately necessitate the closure of a bridge, however; that happens when deterioration means the safety of motorists can’t be guaranteed and the bridge’s load capacity falls to less than 3 tons, according to PennDOT .

Asked about any concerns regarding fracture-critical bridges in Lehigh County, General Services Director Rick Molchany said, “We have no outstanding issues of concerns based upon the PennDOT [bridge inspection] practice.”

He highlighted issues such as climate change, flooding and the loss of sediment around bridge abutments as reasons to continue inspecting bridges, adding that the county’s capital planning would address in part the county’s 14 bridges that have structural deficiencies.

Four of those bridges ― the Walnut Street Bridge, the Pine Street Bridge, the bridge carrying Allemaengel Road over Ontelaunee Creek in Lynn Township, and the Fourth Street Bridge going over Jordan Creek in Allentown ― are fracture-critical and are scheduled to receive some kind of future work, Molchany said. This would include rehabilitation, replacement or review.

He added that the fact the Walnut Street Bridge closed after a regular inspection proved that the review process for bridges works.

The county owns 46 bridges in total.

Northampton County Executive Lamont McClure said area bridges “are appropriately designated and are not a threat to the safety of the general public.” But he also lamented how the county does not receive enough funding through the Lehigh Valley Transportation Study to handle infrastructure needs.

The Lehigh Valley’s draft Transportation Improvement Program (TIP), which is shepherded by the Lehigh Valley Planning Commission, would invest $633 million on 118 projects in both counties, according to its most recent proposal. The plan covers the region’s bridges, as well as roads, transit and traffic safety.

Northampton County owns and maintains 119 bridges. The county’s bridge office is responsible for yearly inspections, routine maintenance and managing major reconstruction projects. Additionally, four bridges are jointly owned with Lehigh County, two of which are maintained by Northampton County.

Spokesperson Brittney Waylen said Northampton County has four bridges under its jurisdiction considered fracture-critical, with three of them closed.

The lone bridge still open, on Old Filetown Road over the Bushkill Creek in Bushkill Township, is rated fair and sees very minimal traffic, Waylen said. It provides access to one property on the road, she said. Township officials did not return messages seeking comment about the bridge, which opened in 1937, according to a marker.

“All of these bridges are inspected every two years by PennDOT’s consultant bridge inspector to verify that no immediate action is required,” Waylen said.

Morning Call reporter Graysen Golter can be reached at ggolter@mcall.com .

Morning Call reporter Anthony Salamone can be reached at asalamone@mcall.com .