Tragedy struck Pittsburgh early Friday morning on Forbes Avenue when the Fern Hollow Bridge on the eastern edge of the city came crashing down onto Frick Park. Ten people were injured as a result of the collapse, with four transported to the hospital with non-life-threatening injuries. Firefighters had to rappel over 100 feet down the steep terrain to the bottom of the ravine to rescue trapped drivers.
It could have been much worse.
“If this would have occurred an hour later, this is a road that gets probably about 15,000 cars on it a day and if it was rush hour, we would be looking at a couple hundred cars down in that valley," Pittsburgh City Councilmember Corey O’Connor said. "We got very, very lucky today.”
Also, a failure mechanism built into the bridge allowed for a gradual collapse. Vehicles were able to ride the falling deck as the bridge as it slowly descended to the bottom of the ravine.
A major gas line attached to the bridge was cut, briefly forcing several residents to evacuate their homes until the gas supply was shut off.
The bridge collapse served as a stark example for President Joe Biden, on a scheduled visit to Pittsburgh, of the urgency in implementing the recently passed infrastructure spending bill, meant to restore the country’s roads and bridges. Less than a year agon, inspectors discovered a significant crack through a critical member of the Hernando de Soto Bridge carrying I-40 over the Mississippi River.
The Fern Hollow Bridge, a rigid-frame steel structure constructed in 1970, had been flagged as being in poor condition by PennDOT inspectors as far back as 2011 and again in September 2021. This will no doubt result in greater scrutiny on the condition of bridges around the country, where over 45,000 are already in poor condition.
The collapse is unsettling for a city like Pittsburgh, famous for its many iconic bridges. Dozens of major structures span the city’s Ohio, Allegheny and Monongahela Rivers and steep terrain. Of those bridges, 29 are already in poor condition and over 50 have at least one poorly-rated major component. Allegheny County, which encompasses the city and surrounding region, has nearly 200 bridges in poor condition. Pittsburgh’s 2022 budget includes $7.25 million for bridge rehabilitations and preservation, a far cry from the estimated $450 million that would be required to complete all of the required repairs to bring the city’s bridge inventory into satisfactory condition.
Pennsylvania Lieutenant Governor John Fetterman, who resides in nearby Braddock was on the scene and called the collapse, “the latest in a long line of preventable, man-made disasters that prove what so many of us in Pennsylvania have been saying for years: Our infrastructure is failing our people.”
“In Pittsburgh, in Pennsylvania, and across America, we cannot afford neglect any longer. It’s time to rebuild this nation,” he continued.
It is important to note that because a bridge is considered to be in poor condition does not indicate that it is on the verge of collapse. A bridge’s overall rating is governed by the primary component – deck, superstructure, substructure – with the lowest condition rating. The deck and superstructure of the Fern Hollow Bridge both received condition ratings of “4 – Poor,” which indicates deterioration of structural elements has advanced. A condition rating of “3 – Serious” would have indicated that the deterioration had begun to seriously affect primary structural components.
That this bridge collapsed dramatically under minimal live loading (light traffic) underscores the unpredictable and difficult nature of aging structures. Old bridges become increasingly fragile and susceptible to failure when temperatures drop rapidly or the soils or bedrock supporting their foundations experience settlement or erosion. As a rigid-frame steel superstructure, the Fern Hollow Bridge would be classified as fracture critical, meaning that failure of either of its primary K-shaped frames would likely result in collapse due to lack of redundancy. Inspectors of fracture critical bridges are held to a higher standard which requires them to perform a full hands-on inspection of every inch of the fracture critical members of the superstructure.
Inspectors had flagged this bridge for over 10 years but had not seen enough deterioration to lower the condition ratings of the superstructure to the point where more significant measures to rehabilitate the bridge would have to be taken. The Fern Hollow Bridge was weight restricted to 26 tons, which indicates that its original structural capacity had been thoroughly analyzed and evaluated against modern live loading and traffic demands.
State Departments of Transportation do the most with their limited budgets but they just can’t tackle every issue at once. But structures don’t slow their rate of deterioration because the government signed a one-time infrastructure funding bill. The high number of bridges in poor condition is the result of decades of underinvestment in infrastructure repair and huge swaths of the national transportation network approaching the end of its useful service life while being tasked with carrying traffic volumes that far outstrip original design.
“[Authorities] do prioritization in bridge maintenance, and sometimes bridges will jump up that list if there are issues,” said University of Pittsburgh professor Kent Harries. “Sometimes they’ll shut a bridge down within hours if they see a serious issue. But the reality is there are limited resources that limit what can be done. Most get neglected and that is a reality that we need to deal with. The infrastructure bill makes a small dent in that.”
There will no doubt be intense scrutiny of the most recent inspection. An investigation into the ultimate cause of the collapse by the National Transportation Safety Board has already begun. Getting to the bottom of what triggered the failure could take over a year as experts in the field of structural engineering, materials science and forensics work to reconstruct the scene, process wreckage, review existing inspection reports and test samples of concrete and steel from the bridge.
“It's kind of like peeling the layers of an onion to see where things were and where they ended up in the collapse,” Dennis Collins, the investigator in charge for NTSB said. “Of course, we're looking for indications of where it began.”
In Pittsburgh, President Biden visited the scene of the collapse and stressed that help is on the way in the form of billions of dollars for investment in reconstruction of roads and bridges across the nation.
“Your governor and your members of Congress, your mayor have been saying for years, ‘we have to do something about this,’” said Biden. “We don’t need headlines saying that someone was killed when the next bridge collapses. We saw today, when a bridge is in disrepair, it literally can threaten lives. There are another 3,300 bridges here in Pennsylvania in just as old, and just as decrepit a condition as that bridge was,” he continued. “Across the country there are 45,000 bridges in poor condition.”
“We’re gonna rebuild that bridge, along with thousands of other bridges in Pennsylvania and across the country because it’s in our interests, for our own safety’s sake and it generates commerce in a way that we can’t do now,” said Biden.
The Fern Hollow Bridge collapse severs a major artery into the heart of Pittsburgh. It will take over a year to rebuild it. The task of rebuilding falls to PennDOT’s who had been planning work on the nearby Squirrel Hill Tunnels, which will now see increased use due to the bridge collapse.
The President’s infrastructure spending bill includes over $27 billion for bridge repair and reconstruction, but it remains unclear how quickly that money will be distributed and spent. It’s clearly too little, too late for the residents of Pittsburgh. Seeing a major collapse in a city known for its bridges is a grim reminder that American infrastructure has been neglected for far too long. Without long-term, sustained investment in drastically reducing the number of bridges in poor condition, this won’t be the last high-profile bridge collapse in America. Miraculously no one lost their life in Pittsburgh, but next time we may not be so lucky.