BONUS: Freeways and loneliness

LA: Certain urban design choices and certain political choices are really robbing people of a happy life.

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LA: This is not only about our opportunity to meet friends and laugh with them, but on the long run, this impacts people's wealth.

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AB: From KPBS in San Diego, this is Freeway Exit. I'm Andrew Bowen. Loneliness has been on our minds in America. It's hard to make friends nowadays. And isolation can do some serious damage to our mental and physical health. My guest on this episode says urban freeways are making that problem worse. Luca Aiello is a data science professor at the IT University of Copen  hagen. He's the lead author of a research paper published last month titled "Urban Highways are Barriers to Social Ties." It's the first study to actually measure — on a large scale — just how much freeways are preventing us from getting to know our neighbors and building community. This research was fascinating to me, and I'm very excited to share it with you… after a short break.

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AB: We're back. Here's my conversation with Luca Aiello, author of the new study "Urban Highways are Barriers to Social Ties."

AB: There's been a lot of research into how urban highways are harmful to the environment, to public health. They create air pollution, noise pollution, obviously greenhouse gas emissions. Why did you want to study the impact of highways on our social ties?

LA: Well, in a way, in the past, people have also looked into the impact of urban transportation on social connections, but they've done so in ways that were very qualitative and without a large scale quantification of this. Imagine it's easy to use devices to measure pollution around, noise pollution, air pollution. But if you have to actually measure social connections and how much these are disrupted by urban infrastructure, this all of a sudden becomes very hard to do. In the past, people have thought about it. We're not the first people thinking about this thing, but they've done it in ways that were very qualitative and small scale. One, I think, very famous example and very well-known example, at least in the urban science literature, is the exercise that Donald Appleyard has done in the '80s. Donald Appleyard basically went measuring by hand the number of social connections, interactions between people, living across the street for three different streets in San Francisco with different level of car traffic. So high-speed traffic versus low-speed traffic and different also volume of traffic. In this seminal contribution and book, he found that there was a very, very strong effect of the volume of traffic on social connectivity and self-declared social connectivity. This is the closest example that we had so far to a quantitative measurement of impact of large streets on social connectivity. People have thought about it, but never were able to measure it on a large scale, so that's why we thought about it. Also, another reason is we are a team of data scientists, most of us also focus on urban data science, and we look at cities from the perspective of city dwellers, and to try to quantify aspects that might impact the quality of life in general of people. Obviously, social connections are things that correlate a lot with individual opportunities, happiness, also health and satisfaction. So we thought, Okay, so this is a piece that is really missing from current urban data science research that we need to fill somehow.

I've been wanting to conduct this study for many years, so almost 10 years, but never found the appropriate data to do so. A couple of years ago, we assembled this team with the appropriate data, and now we were able to do it. This motivation also comes from our perspective in the sense of quantifying things that might be beneficial or harmful to people living in cities.

AB: We'll definitely dig more into your data and your methodology, but let's go back to a simple and basic question that probably is maybe self-evident to some people, but why are social ties important? Why is this something that we should care about?

LA: Absolutely. If you look at the literature in social sciences, so I'm talking about 100 years of literature, there is plenty of evidence, qualitative and also strongly quantitative evidence that social ties are basically the most important thing that we have in our lives. Social ties determine many outcomes, positive and negative outcomes in our lives, starting from, for example, economic opportunities. People who have strong connections and strong combination of strong support ties and also weaker knowledge exchange ties are those who can find a better job, being resilient to lose a job and find another. The equation between strong social ties and also higher opportunities in terms of economic progress, it's something that has been shown extensively. But also happiness, a self-declined happiness. Many studies quantifying very clearly the fact that the self-perceived satisfaction in life is really determined by a healthy network of social connections. And also, how long do we live? We tend to live longer if we have a strong social networks of support. Social ties are crucial for most positive outcomes we care about, in a way, both at an individual level and also at regional level. Something that, for example, especially the US audience, because we were also talking specifically about US and the fact of this I was in the US, and what this audience maybe doesn't realize too much is that social connections It's not just a synonym of leisure or having fun together, but directly affects the wallet of people.

Having parts of your urban infrastructure that actually impact social connection, ultimately down the line, steals money from you, especially if you come from a poorer class. This is why I think it's crucial to be able to provide quantitative, solid evidence about the impact of different elements of our cities on social connections.

AB: This research is coming at an interesting time because, at least in the United States, we are having conversations about loneliness, about obviously it's important for people to have friends and feel happy. It's important for people to have economic opportunities. But a lot of people have drawn a line between the loneliness that people feel and people turning to extremism, for example. There seems to be a real conversation we're having about why it's important to know people, to have friends, to have those social ties, and your research really fits into that.

LA: Absolutely. So the The study of the rise of loneliness in the US or in North America has deep roots. It starts from the '80s, the famous book Bowling Alone, right? So saying more and more people go to the bowling alley playing alone. I think this crisis aggravated even further with the spreading of consumer Internet of the web. Of course, the increasing fragmentation also the political spectrum and society in general, clearly stems from more aggravated forms of isolation of people. They feel isolated and abandoned in a way as well. So this ties directly into what we study, because then it becomes completely crucial to understand what are the elements that need to be added or removed from our lives to actually patch back this very big loneliness problem.

AB: Explain to me your hypothesis. Why would living near a highway or in a city with a lot of highways have an impact on how many friends you have, how many people you know?

LA: Highways are very large pieces of transport infrastructure. Many of your listeners from the US are probably familiar with these very, very multiple lanes, highways, cutting through the center of very large cities in the US. The very simple explanation, is that those concrete monsters are literally hard to cross. If you live on one side of this highway, it's for you literally very hard to go and reach a place that's sent at the other the other side of the highway. Here, the hypothesis is that by having a highway nearby, you are constrained in your short-range mobility. You don't walk around as much as what you would do if you had nice paths around running through gardens. This thing happened in the US because there's been a very explicit policy of building a highway network in a certain way, and I think we'll get into that at some point. As a result, the culture has developed in a way that people tend to move preferentially by car. This type of habit has been aggravated in a way by the rhetoric around cars and behind the use of cars. The car has been for many, many years and decades synonym of freedom.

With a car and access to high-speed transportation thought for personal car transportation, you would be free to access any place in the city, and therefore, have a lot of opportunities. It turns out that actually, sure, you can move around relatively fast. Modulo traffic, of course, which plagues most American big cities. But what you lose there is your ability and habit to move around locally. So as a result, result, if I might have maybe a potential friendship to be built, but my potential friends are at the other side of the highway, this friendship will never happen. That's the intuition. Now, this, I think, is something that people can intuitively understand. The question then became how to actually measure it. But this is clearly a different story.

AB: So your paper is based on a data set of about 1 million Twitter users and posts that they made to this platform in 2012 and 2013. How did you settle on this data set as a basis for trying to answer this question of freeways in their impact on our social networks?

LA: First of all, we need to understand what would be the ideal data set to answer this question. What we would like to have is clearly a map of a city because then you can understand where all the infrastructure is laid and all the different maybe even natural elements are to understand what might be potential barriers between different maybe home locations. Then When you want to overlay onto this map a social network. The social network, ideally, would be a network where nodes in the network are home locations, so where people live, and links between home locations represent friendships or close acquaintances in a way. Now, this type of data is extremely rare for many reasons, privacy reasons and everything. But back in the days, what Twitter was doing was to, by default, geo-reference with a verifying granularity all tweets that you were posting from a mobile device. This was a default behavior that then was discontinued. But in the early days of Twitter, this was the default. This means that for many users who used Twitter frequently on their mobile devices, you can estimate roughly where they live. And not only that, you also have the network of mutual followership, which in a way could be validated as a relatively good proxy of friendship in a way.

So the reason why we settled on that specific data, which is, again, not terribly recent, is because of this particular feature that Twitter had back in the days that allows you not only to draw the network, but also to locate create people, especially in the city at a very fine-grained granularity with an error of maybe 100 meters.

AB: So I follow this guy, he follows me back. That is counted as one social tie. From these 1 million users, you establish about 2.7 million social ties in the 50 largest cities in the United States. Once we've drawn these lines across the maps, establishing this knows that person, the question then becomes what exactly?

LA: Here the hypothesis is that we should be finding fewer social ties crossing highways than expected. Here, the magic and important keyword is then expected. In a world, in a counterfactual scenario, in an In my imaginary world, without highways, you would observe more ties crossing the path of the highway compared to the real data in which the highways are actually there. Here, what we did is a little bit of a statistical trick in a way. What you do is you measure the number of ties crossing an highway between two areas in the city, and then you compare this number of crossings with the number We are crossing from a synthetic model where your social network is reshaffled at random in a way that we are preserving the basic properties of this network, for example, how many people I follow, the special distance of my friendship. But the reshuffling, in a way, ignores the presence of whatever is on the ground. In this imaginary world, people connect with one another, disregarding the presence of highways. We then compare this randomized, reshuffled imaginary world with the real data, and the expectation is that we're going to be finding way fewer crosses in the real data than in the simulated data, because the simulated data would cross more because the highway is not there.

By combining these two numbers, we calculated what we called a barrier score. A barrier score is high, is positive when we have, again, fewer crosses in the real data than the simulated one. What we find is that in all the top 50 US cities by population, we find positive barrier scores for most highways and in aggregation for for all the highways in the city. We see that these barrier scores are particularly high for pairs of locations that are at a relatively short distance. By short distance, I mean between one and eight kilometers. So this barrier effect is especially high if two people live at a distance between 1. 8 kilometers, so a relatively short distance. Whereas, of course, if you go longer distances, for example, you live 20 or 30 kilometers apart because some Metropolitan areas in the US can be very large, then you might see that the barrier score becomes, in some cases, even negative because a highway might actually facilitate you transporting from one place to another. But consistently for all these cities, we see that for small and medium distances, the barrier effect is very, very strong.

AB: Really brilliant design of this study, I have to say. You tested the strength of these data and these assumptions that you were making in a lot of different ways, didn't you? In order to be confident in your conclusion that highways are creating barriers to social ties, you really want to make sure that it's the highway creating that barrier and not something else that you might be missing that's not accounted for in these data. Can you explain this confidence testing that you did?

LA: Absolutely, because clearly, connectivity might depend on many other factors. First of all, other barriers. So for example, a river, or maybe a railway.

AB: We have lots of canyons in San Diego as well that are barriers, yeah.

LA: Of course, any hills or even a bay or whatever. But then you also have less tangible elements that might influence are reduce connectivity between areas which are racial or socioeconomic factors. It's well known that you do have areas that have a certain socioeconomic standing, connecting between each other and so on and so forth. What you want to really do here is to have a set of models that check for the presence or absence of all these factors, and discount the barrier effect you find by all those things. We did a bunch of tests for each of these factors. In the case of socioeconomic indicators, what you do is you run what are called the regression models. Basically, it's statistical models that put together many factors and give a weight to each of these factors to see whether after the addition of all of them, the relationship between connectivity and highway presence is still significant, statistically speaking. That's one way in which you can do it. Then you can also have other checks. For example, Try to restrict your analysis to patches of ground that are actually free from any other physical barrier. You take a patch in which inside the patch, we have no rivers, not highways, no nothing, but only highways.

You see how your model behaves inside those patches. These are two examples of how you could check for different confounding effects given by other factors. What we find is indeed that the analysis survives systematically all these checks, which speaks to the really high strength of this barrier signal, basically in all scenarios and situations.

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AB: Coming up, the city where freeways are hurting our social lives more than anywhere else in America. Where does San Diego rank? And which freeway here is the biggest barrier to friendship? Stay tuned.

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AB: Hey, we're back with more from Luca Aiello, data science professor at the IT University of Copenhagen.

AB: So you established this barrier score for each city that measures how much highways are preventing people from establishing social ties. The highest score, or the city with the highest score was Cleveland, Ohio. I've never been to Cleveland, but I did take a look on Google Maps, and it does have a lot of highways in the urban core. Can you talk more about Cleveland and what it has in common with these other cities that are at the top of the list with high barrier scores?

LA: Absolutely. We find very strong signals for several cities. As you say, Cleveland was one of those. The common interpretation for these high barrier scores ties very often with the history of racial segregation in the US. You will find highways with extreme extremely high barrier scores in either two categories of cases. The first being interracial barriers. You have a highway that very, very sharply separates two neighborhoods. One one that is majority black and one majority white. This is extremely clear for cities like Oklahoma City, where you have the I235 that separates basically these two types of neighborhoods. Same thing goes for Detroit, the very famous 8 Mile Road in Detroit. What you can see there, it's really, really striking, extremely high barrier score on these transportation segments, and that sharply divides black and white. The second category is instead, intraracial barrier scores. These are examples of highways that were historically, and this is clearly well-documented, built to purposely disrupt black neighborhoods. This is very evident, for example, in Columbus or even in Nashville. Nashville, I think it's a very telling example where the I-40 was specifically rerouted to disrupt a very thriving Black neighborhood. This was done with a certain political design.

This is a part of American history. It's something that is, I don't think it's debatable. It's documented in many ways. Systematically, what you find, if you look qualitative relatively at all these examples, is that high barrier scores indeed relate very intimately with the history of racial segregation. Now, the very curious thing is that this effect of barrier persists even after these racial boundaries, maybe over the years, fade away. This means that all future generations will still pay the debt of these very large infrastructures actually destroying our social life, even if the racial blending has a again, blend away all the differences in terms of ethnic distribution across areas. So it's clearly a signal of very disruptive choices that people are going to be paying for many, many years and decades to come, if not fixed somehow.

AB: San Diego was closer to the bottom of the list, which I found rather interesting. Of the 50 most populous cities in the United States, it came in 38th place, meaning our where highways still do create social barriers, but perhaps not as much as other places. Any interesting findings you can share about San Diego specifically, or those cities where the data suggests highways aren't quite as damaging to our social lives?

LA: Again, so one thing to be kept in mind here is that, yes, we did this ranking of cities, and the ranking takes into account an average effect of highways within the Metropolitan area. This doesn't mean that San Diego is free from the problem, because if you look at specific highways and specifically some bands of distances, this effect can be actually very, very strong. For the case of San Diego, specifically, we have very high barrier scores for people living between 2 and 6 kilometers apart. That's a very strong signal there. We have extremely high barrier scores for the Interstate 805, basically from the area of, I think it's called Norman Heights, down to Mexico. That whole segment is extremely high in barrier score. But also the I-5, separating downtown from the rest of the city, is very, very evident in terms of signal. Two of the, I believe, largest highways or motorways that are in San Diego are actually having an impact which is very, very high.

AB: Yeah, that's interesting that the 805 really stands out as a really high barrier to social ties because it's surrounded by a lot of really dense neighborhoods and fairly walkable neighborhoods, too. So you mentioned normal heights on one side of the 805. On the other side is North Park, which is these two very urban hipster neighborhoods where people walk. You can walk to the bar or the cafe or something. But crossing that freeway takes a lot of effort. It's almost like a mental barrier for some people, I think, that Sure, it might be a 10-minute walk away, but that freeway is really unpleasant, and it's just not a place that we want to go around. So do you find that the size or scale of these freeways can impact the likelihood likelihood of people crossing them and actually establishing friendships across the highways.

LA: Yeah, absolutely, Andrew. I really love what you said about the psychological perception of this. We clearly cannot give an explanation about why this happened, so we can only hypothesize. But one piece of evidence that goes towards the psychological interpretation is that this barrier effect is found even after discounting for the actual walking time that you have from one location to another. It's not because the presence of this highway constraints you in finding a longer route to reach your friend, but it's really just because it's there. This, I think, corroborates a little bit the interpretation about the psychological factor structures being a very important explanatory variable to the effect that we find.

AB: Really, what you're saying is it's not just the distance that we have to travel in order to cross a freeway, it's also just the fact that the freeway is there. As you say, we could hypothesize or theorize about what it is about the presence of the highway. There's certainly more noise there. It's maybe not as safe for pedestrians to cross because there are on-ramps and off-ramps where you have to deal with vehicles. It's just something beyond just the distance. It's also another barrier effect that we haven't quite figured out how to quantify.

LA: Exactly. Absolutely. Yes.

AB: You mentioned in a few cases that you found highways actually increased the likelihood of social connection, especially across long distances. How does that work?

LA: From the perspective of the numbers we crunched, what you witnessed is that these barrier scores I mentioned actually become negative for very long distances. We see this inversion of the sign or the barrier score on average around 20 kilometers. The interpretation there is that if you live 20 kilometers apart or more, most likely, given that in the US, on average, the public transportation system is maybe not as well-developed than in the average European city, let's say, you are going to reach your friend using the car. The presence of a highway in between you and your friend might actually facilitate the connection compared to what our synthetic model would expect in the average case or the random case. So that's the interpretation.

AB: And this was really the promise of highways when they were sold to the public in the mid-20th century, wasn't it? That highways are not dividing neighborhoods, they are connecting neighborhoods and doing so across long distances. After doing When you're doing all of this research, how true do you think that that premise or that selling point was?

LA: It is true to a certain extent. Of course, highways are facilitating high-speed transportation using personal vehicles. That's clearly true. But again, the right question to ask here is at what cost? At the beginning of our conversation, you already mentioned the problems that pertain to environmental disruption, so pollution that goes into our air, so air pollution, noise pollution. Also, one thing that we did mention is all the space that the infrastructure takes from our cities, counting highways, but also parking spaces. The sheer amount of parking spaces that American cities allocate because of parking laws and because of the history we're very familiar with, Andrew, of course, is humongous. So you are literally stealing space from all other uses that can be also dedicated for developing maybe social enterprises in a way. So that's one part of the story. So we are polluting the air, we are stealing space from people. But also now with this study, we can really put a number of how much your ability to move around and connect locally is disrupted by this slight increase in your opportunity to move long range. Now, do we really want to hold on to that small advantage while sacrificing our air, the beauty of our neighborhoods, and also our chances to meet more people locally and experience our cities in ways that are happier and healthier in a way. So that's the real question. My biased answer is that it's probably not worth it. But again, this is for the public to decide, I guess.

AB: I want to go back to what you said about socioeconomic factors and how they play into social ties. So I'll read the sentence from your paper. It says, Highways may be as influential as socioeconomic factors in contributing to social fragmentation. Let me try and explain this, and you tell me if I'm right. Let's take a corporate lawyer and a school cafeteria worker, two people from very different sides of the socioeconomic spectrum. You could look at the fact that they don't know each other and aren't friends and explain it by the fact that one makes more money, the other makes less money. You're saying that the existence of a highway between these two people is equally plausible to explain the lack of a social connection there, that socioeconomic factors do play a role, but highways could play just as important a role in explaining why people are not connecting and establishing friendships.

LA: Exactly. The key way of interpreting this is that the two effects compound. Imagine the decrease in likelihood of creating a social tie between two people that come from very different socioeconomic backgrounds. The example you gave is very intuitive. One would imagine that it's maybe very unlikely these two people would mix together, and it seems something highly likely, highly probable. Imagine that this effect is as strong for highways. A highway would reduce likelihood of connecting as much as differences from socioeconomic background. And again, I want to emphasize these two things sum on top of each other.

AB: I looked at your CV and you've lived in a lot of very different cities. So in the United States, you spent time in Bloomington, Indiana, and Sunnyvale, California. And then in Europe, you've lived in Barcelona, London, Turin, and now Copenhagen. In all of these places that you've lived, what have you noticed about how the infrastructure can make it easier or harder to find friends?

LA: Oh, man, absolutely. When I used to live in Sunnyvale, I was working as an intern for Yahoo. You remember Yahoo, probably, right? At the time, I stayed there for three months living in a hotel, and I was walking to the office. It was relatively close But I had to cross so many highways to get there. The experience was so unpleasant. But I did it anyways because I was used to maybe walk around. But clearly, if you compare all the cities you listed, the experience can be very, very different in a way. You can see how the urban infrastructure and the transportation infrastructure has a very big impact on it. So take a city like Barcelona. Barcelona is a city that has invested a lot in active mobility, for example. With bike sharing, they have been pioneering the concept of urban design for walkable neighborhoods with the concept of superblocks. Basically, you take a bunch of blocks and you group them together and restrict the car access inside these superblocks. This has proven to be very effective, and several other cities in Europe are considering very similar measures. Here in Copenhagen, transportation by bike is the norm, and I have been very much welcoming this change in my life.

For example, coming from London, where biking around is possible, but relatively dangerous given the heavy car traffic, especially in the city center. So Actually, the design of our cities impacts our daily lives in ways that perhaps we don't realize, especially if we don't experience several different urban environments, and not many people have the means or the luck to do that in their life. I believe that this type of studies, and also thanks to people like you, Andrew, trying to explain these things to the general public is very important to make people realize that they should deserve better from their cities and demand better. To realize that certain urban design choices and certain political choices are really robbing people of a happy life around their homes. This might be, again, very evident to me. I've been around a little bit I am actively studying these things. But perhaps certain people give for granted that everyone should move around by car. This also in Torino, my home city. Torino is the city where Fiat was born, so the automotive industry of Italy. The car culture is so ingrained into the brains of people there that Turin would be a completely ultra-walkable city if people wanted to, but people stick to cars because that's the tradition.

Raising awareness about a possible future without cars, or at least with less cars, is something we need to keep doing because in many cases, with relatively little investment, this is possible. It's just a matter of step-by-step changing habits.

AB: What are some of the differences that you've noticed between highways in Europe and highways in the United States?

LA: Well, first of all, I wish we had a similar data set also for Europe, which we don't, at least at the moment. One of the main differences that you have in Europe versus the US is that very rarely, or at least more rarely, you have very large highways crossing densely populated city centers. And so maybe you have some configurations like rings of highways around cities like see, London, for example. But you don't have a highway passing through the center of London, close to the Big Bang. That, I think, is one of the main differences that ultimately impacts the way in which this piece of infrastructure have on social life. Therefore, I would expect, in lead differences, but the principle doesn't change.

AB: Luca, what do you hope urban planners, policymakers do with this research that you've provided them?

LA: I think our research provides ways to target the problem effectively. Now, all of a sudden, you can have a very detailed map of which segments of a highway are particularly damaging. You can always try to invest resources sources to fix these problems. Actually, to be very fair, in the US, you have tried to do that. In 2023, the Department of Transportation has allocated a lot of funds to reconnect communities that were disrupted explicitly by highways. This program allocated money to local communities in different states, and effectively, what this has achieved was to even just simply building bridges on top of highways, to reclaim the connectivity space that could maybe bring together people living in different neighborhoods. This is clearly costly, and these are endeavors that take a long time, but it is possible, again, given the political will, because this program has been discontinued this year with the new administration, And again, if the political will doesn't align with certain objectives or even interpretation of how life in the city could be, then clearly it's impossible to achieve anything. What I would say is that the general public should, after being aware of the problem, try to make some decisions ranging from maybe activist campaigns down to even be vocal with local representatives to actually invest attention and resources to this. Because again, I want to emphasize that this is not only about our opportunity to meet friends and laugh with them, but on the long run, this impacts people's wealth, economic wealth, which is something that I believe many people care about as well.

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AB: That's it for this bonus episode. It's been a while since it happened, but thank you to everyone who showed up to our group hike and listening experience along the 163 freeway in Balboa Park. It was really fun meeting listeners and hearing their thoughts about the podcast. And it was great seeing people meet each other and chat about their common interest in urbanism. There are a lot of forces in this world trying to keep us apart. And I really hope this podcast can be a force that brings people together. I hope to do more of these events in the future, so keep listening. And keep telling your friends about Freeway Exit, and leaving us those ratings and reviews on your podcast app. They really do make a difference in helping us grow our audience. Thanks for listening, and for donating to KPBS.