Pittsburgh’s Bridge Collapse Spotlights America’s Infrastructure Woes

12:09 minutes

looking over the ledge of road of a collapsed bridge in snowy woods. bus is trapped under a large piece of debris
The collapsed Forbes Avenue Bridge in Pittsburgh on the morning of January 28, 2022. Credit: City of Pittsburgh

Our modern world is made up of infrastructure: Roads, buildings, and bridges all play a big role for many people’s daily lives. If these structures do their jobs well, we don’t think much about them. That is, until infrastructure fails.

Bridge collapses are especially scary, like the structural failure in Pittsburgh, Pennsylvania last month. These events are shocking, and cause people to wonder how this could be allowed to happen. But looking at the numbers, it’s actually surprising there aren’t more failures.

According to the American Road and Transportation Builders Association, a third of bridges in America are in need of repairs or replacement. Moreover, seven percent of the nation’s bridges are considered “structurally deficient.” And the problem could accelerate: Larger vehicles, more traffic, and climate change put a greater strain on bridges that already need regular maintenance.

Joining guest host John Dankosky to talk about the engineering jargon around bridge infrastructure and new ways of building more resilient structures is Abbie Liel, professor of civil, environmental and architectural engineering at the University of Colorado in Boulder. 

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Segment Guests

Abbie Liel

Abbie Liel is a professor of Civil, Environmental and Architectural Engineering at the University of Colorado in Boulder, Colorado.

Segment Transcript

JOHN DANKOSKY: This is Science Friday. I’m John Dankosky. We’re surrounded by infrastructure, roads, buildings, bridges, and if these things do their jobs well we don’t really think about them at all. That is, until infrastructure fails. Bridge collapses are especially scary, like what happened in Pittsburgh, Pennsylvania just a few weeks back.

SPEAKER 1: Three to four vehicles, including a bus, were on the bridge when it collapsed. 10 people, including first responders, sustained non-life threatening injuries. Three people were transported to the hospital.

JOHN DANKOSKY: Our first thought is, how could this happen? But when you look in to the numbers, it’s actually surprising there aren’t more bridge failures. According to the American Road and Transportation Builders Association, 1 in 3 bridges in America needs repairs or replacement. But what does that really mean? And how do we make our bridges better and more resilient? Joining me today is my guest, Abbie Leil, a professor of civil, environmental, and architectural engineering at the University of Colorado, in Boulder, Colorado.

Abbie, welcome to Science Friday. Thanks so much for being here.

ABBIE LEIL: Hi John, thank you so much for having me.

JOHN DANKOSKY: Well, let’s dig in to this report from this year about the state of the country’s bridges. And it found that more than 43,000 bridges in the US are structurally deficient, or poor. Now, that sounds like a pretty alarming number, but the truth is, I really don’t understand what those words mean, what structurally deficient means, and how it is different from poor. How worried should we be about these numbers?

ABBIE LEIL: I think we should take that as a warning sign to give that bridge more close evaluation, right? So it’s kind of like, you go to the doctor and they tell you, oh, there are some indicators of things that might be wrong, but we need to do some more tests, we need to do some assessments, and then we’ll figure out a strategy. So the reality is that some of those bridges are probably structurally deficient in a way that we really wouldn’t want to drive on them, and then some of them are, oh, we should really prioritize doing something about certain parts of that bridge, but we’re not worried about it failing tomorrow.

JOHN DANKOSKY: When we talk about 1 in 3 bridges needing repair or replacement, those are two very different things. Replacement sounds like that instance where we shouldn’t be driving across that anymore, and it needs to be torn down and rebuilt. Repair sounds like maintenance. It sounds like something that we have to just do all the time. Like you said, a checkup going to the doctor.

ABBIE LEIL: Yes, I think we have this massive amount of infrastructure. We’re trying to monitor it in the same way that our doctors are trying to keep track of all the possible things that could go wrong with each of us, and apply the best preventative strategy. And our infrastructure is super complicated to maintain and replace, right? Because we have this complicated set of owners, so basically all levels of government, who are trying to manage that job of understanding what most needs repair, what needs replacement.

And some of the things that need replacement need replacement because they have big problems for resilience, and some of the things that need replacement need replacement because where and how we drive and the vehicles we drive have changed, and so they’re just not appropriate for the infrastructure of today. So there’s all of these things that are kind of mixed together in thinking about what we should do about upgrading our infrastructure.

JOHN DANKOSKY: Well, you’ve mentioned some of them, but maybe we can go through some of the factors that go in to a bridge degrading over time. What causes it to wear down and to need repair or replacement?

ABBIE LEIL: There’s really a number of factors that play in here, right? So one of them has to do with the materials and the components of the bridge themselves, and this might be the one we often think about. So usually these bridges are reinforced concrete and steel. So, what is the condition of the steel? What is the condition of the connections between steel components? What is the condition of the reinforced concrete? What is the condition of the reinforcing steel within that concrete?

And those materials wear down over time. Many of these bridges are quite old, over 50 years old. They might have been overloaded or overstressed at some point in their lifespan. They also might have seen some deterioration from things like salt, or something put on roads that causes corrosion, or just corrosion from everyday being out in the environment.

So that deterioration in the materials and the components, that’s one important aspect. I also mentioned changing use and functions of bridges is important. Some types of vehicles have gotten heavier. Semi-trucks are heavier. We drive different places more often, different traffic patterns than we used to have. And that can affect the condition of the bridge if you’re changing the loading scenario.

We also have a changing climate, which comes with it changes in rain and flood risk near coasts, coastal flooding, wind effects. They can accelerate the deterioration of a bridge compared to what it would if we didn’t have that changing climate. It may also change the loading scenario. We might be more worried about scour of some bridges now than we would have been, even a couple of decades ago.

JOHN DANKOSKY: Why do you think that bridge maintenance has fallen behind across so much of the country? Why do we have so many bridges in need of repair or replacement?

ABBIE LEIL: I like to think about it like our houses. So that’s the piece of infrastructure I think we’re the most familiar with. So I don’t know what kind of resident you are, but my husband and I don’t do maintenance until the last possible minute. Like, the thing has to break before we’re going to do something about it. And that’s a piece of infrastructure that I am intimately familiar with. I see it every day. I know what I want from it.

And some owners are not like that, or some residents are not like that, right? They call their landlords much more quickly, they monitor their infrastructure more closely. Then you think about that problem, so that’s the home problem, and you extend it to all these infrastructures, all of these owners, and the fact that maintenance is just not very glamorous. Right?

In our political and governance climate, it’s easier to justify new shiny things, and a reinforced concrete bridge that needs a new deck– it’s not a glamorous choice, and in fact, it can be really disruptive, right, to do that maintenance, for the traveling public.

And so there’s a lot of challenges with the owners of this infrastructure, and actually making the decision to get that done, and, of course, finding the funding to get that done, because these are expensive projects. And again you can think about home maintenance, right? We spend a lot of money on our homes, and our infrastructure is much more expensive than that.

JOHN DANKOSKY: I think one of the things that’s interesting Abbie, is you mentioned this before, we expect things like our homes, but also the bridges we drive across, to last 100, 150 years. Is that realistic? That we should be driving across a bridge that was built around the turn of the last century?

ABBIE LEIL: Our infrastructure is amazing, and some of the ways that we build have really truly stood the test of time, right? On the other hand, if you think about the things in your house, just to go back to the house example, none of those are a hundred years old, right? Our furniture, maybe that’s old, but our appliances, our cell phones, right, those things are 10 to 15 years old, typically. And so I think we expect something different from our civil infrastructure than we do from almost every other thing we use or engage with.

And to bring this back to maintenance, I mean, yes, a hundred year old bridge can be just fine, but it’s not going to be just fine if you just leave it, right? We want to monitor it, make sure it’s not having troublesome problems due to weather, or loading, or other issues, or else we really do run in to a problem.

And the design lifespan of bridges is typically considered to be about 50 years. And that doesn’t mean that at 50 years, put a rope across it and we can’t use it, but it does mean that we want to be cognizant of the risks of aging and deterioration, and how to address those problems.

JOHN DANKOSKY: We’re always on the show trying to think of ways to make things better if we can. And so in your world, amongst people who study this stuff, what are you seeing as far as strategies for building better, more resilient bridges. If we have to replace a bridge now in 2022, is there a way to make it so that we don’t have some of the problems that we’ve been encountering with our current infrastructure?

ABBIE LEIL: Yeah, there’s some really cool advances in civil engineering technology, and related to bridges. And both on the construction side, as well as on the design side. So just one example that I was involved in has to do with earthquake resilience of bridges, which is another challenge, because our understanding of seismic forces has changed over time. And so we want to make sure that new bridges are seismically safe and operable after earthquakes, if at all possible.

And so one of the technologies that’s been developed recently is a bridge column, or column or pier system, that is several precast segments, so built separately, and separated by a smooth sliding layer. So when an earthquake comes, instead of that column cracking, and rebar buckling, and things like that, the deformation and the energy demand from the earthquake actually just causes those pieces to slide relative to each other. And the appeal of that kind of technology is that the energy dissipation is in a place and in a way that you expect, and that’s easy to repair.

And so the idea is, first of all, that you wouldn’t get as much damage in that kind of system, but also that repairing that damage would be much easier. In this case you could just slide those pieces back into place. And so that disruption after the earthquake would be much less. There are a lot of these kinds of technologies that we could be using to build faster, to build more resilient, as we think about upgrading our bridge infrastructure.

JOHN DANKOSKY: That’s really cool technology. I’m wondering how much you’re thinking about those other issues that we talked about earlier. The fact that we’re driving more cars, and heavier cars and trucks over bridges more often, the fact that we’re dealing with the effects of climate change. Are those being engineered in to the bridges that we’re building today?

ABBIE LEIL: As a civil engineering community, we’re working really hard on that. Our building codes and standards are in the process of incorporating climate effects, and some of the loading scenarios that we’re working with. And I personally have been involved in thinking about how we might incorporate climate change effects, in terms of our snow loading on structures. So we’re moving that way.

I think civil engineers as a profession, we very much understand the challenges of the changing climate, and we see it as our obligation, our opportunity to incorporate that knowledge in to what we’re doing. And it is happening in various places, and in various types of infrastructure, more quickly or less quickly.

JOHN DANKOSKY: Now we mentioned this earlier. People don’t really think about the bridges that they drive across until something terrible happens, like what happened in Pittsburgh, or the Minnesota bridge collapse of several years ago. I’m wondering what you think it will take for politicians to spend more time thinking about our infrastructure, and the changes that need to be made right now, and also in the future.

ABBIE LEIL: I think that we are seeing more challenges to our infrastructure now than we have previously. And my optimism says that as those events are making us more aware of our infrastructure, and how much we rely on it, that I hope that can help us motivate to invest more in it, recognizing that infrastructure is really central to our way of life, is central to our health, is central to our safety. And so we really do need to prioritize investment in that infrastructure.

JOHN DANKOSKY: Abbie Leil is a professor of civil, environmental, and architectural engineering at the University of Colorado in Boulder, Colorado. Doctor, thanks so much for joining us. I really appreciate your time

ABBIE LEIL: Thank you, John.

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Meet the Producers and Host

About Kathleen Davis

Kathleen Davis is a producer at Science Friday, which means she spends the week brainstorming, researching, and writing, typically in that order. She’s a big fan of stories related to strange animal facts and dystopian technology.

About John Dankosky

John Dankosky works with the radio team to create our weekly show, and is helping to build our State of Science Reporting Network. He’s also been a long-time guest host on Science Friday. He and his wife have three cats, thousands of bees, and a yoga studio in the sleepy Northwest hills of Connecticut. 

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