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As temperatures rise, this research could help cities stay cool

Innovations such as ‘cool pavement’ have the potential to cool down roadways and make walking and biking more pleasant

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A growing number of cities are searching for strategies to offset the effects of higher temperatures on their communities. In the D.C. region, eight of the 10 hottest summers on record have occurred since 2010, according to The Washington Post’s Capital Weather Gang.

Ladd Keith is an assistant professor of planning and sustainable-built environments at the University of Arizona’s College of Architecture, Planning and Landscape Architecture. Keith and a team of researchers are exploring how communities can create “cool corridors” that take into account thermal comfort and safety. In one project, they are collaborating with the city of Tucson to examine whether innovations such as cooler pavement surfaces can make walking and biking more tolerable and extend the life of streets and roads.

Keith said it’s important for leaders to understand the effect rising temperatures can have on communities and why cities should consider incorporating heat-resilience strategies into infrastructure planning. He’s also co-author of a guidebook on how communities can plan for urban heat resilience. This interview was lightly edited for length and clarity.

Q: What drew you to this particular area of study?

A: Before I came back to academia, I was co-chair of the planning commission for the city of Tucson and became really interested in how cities are planning for climate change. This was around 2005, 2006. I realized most of the resources available to communities related to climate change back then were all for coastal communities. But back then there was almost nothing available for cities that were dealing with [extreme heat]. That’s really changed, particularly over the last three years.

Q: So heat sometimes gets overlooked because you can’t see it, but you can certainly feel it.

A: It’s a little bit ironic because the fingerprint of climate change is literally rising temperatures. Yet that’s the last thing that we’ve planned for. And so cities are just really, really far behind with how they plan and govern it. If you look at how many flood plain managers and flood risk professionals there are around the United States, there’s tens of thousands of them. And we currently only have three dedicated staff people in offices in Miami, Phoenix and Los Angeles who specialize in heat. So even though it’s the No. 1 weather-related killer, we’re just not addressing it very well.

Central states and Southwest to swelter as new heat dome builds up

Q: Can you explain what the concept is behind cool corridors?

A: I would describe it as a multimodal transportation route where thermal comfort for pedestrians, bicyclists and transit users is prioritized as a critical design feature. The goal is to increase thermal comfort along these core corridors through the use of heat mitigation strategies. Features like trees or building new structures, increasing urban greening vegetation — and particularly for transit users, improving transit stops and bicycle parking. You can imagine other features — fountains for drinking water, things like that.

Q: Here in D.C., we’ve been looking at travel corridors in terms of speed and safety, which is where bus shelters come into this, but it sounds like there should be more thinking about not just those elements, but elements that can also control the temperature?

A: Absolutely. And I think regionally across the U.S., cities are just so different with so many climates and different natural vegetation. So what counts as a cool corridor in a place like Tucson might be very different than Washington, D.C. And so I think there’s a local flavor to cool corridors to consider. But the idea is to elevate and integrate the idea of thermal comfort for pedestrians, bicycle users and transit users.

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Q: Can elements that help with heat also potentially help places with cold?

A: That’s a good question. Some elements would certainly be the same — better sheltered bus stops or streetcar stops or light rail would certainly help with both the cold and the heat. So you can look at thermal safety in both directions, for sure.

Q: How can cool corridors make cities more livable? And can they make some types of commutes more comfortable for people?

A: The idea is to make walking and biking more comfortable and safe for the entire community. But particularly, it’s an equity issue because for community members that may not have transportation options besides walking or biking or transit, they’re exposed to extreme heat during their daily travel. For vulnerable or marginalized community members, cool corridors can really be a public health, a public safety issue. There are a lot of broader benefits, too. The transportation sector is one of the primary drivers of greenhouse gas emissions in the United States, so if we want to reduce the greenhouse gas emissions that are leading to warming temperatures, we’re going to have to help make non-vehicle transportation options more feasible and appealing.

Q: Are we seeing cities start to incorporate heat resilience into their planning?

A: The city of Phoenix just this spring began planting a lot of trees along one of its first officially designated cool corridors. The city of Los Angeles has a program that has a goal of combining cool pavement along with urban forestry in some of the city’s hottest areas. One of my favorite examples is Las Cruces in New Mexico, which is obviously a much smaller city. They had cool corridor pilot projects back in 2018. So they were one of the pioneers in this. I like to point to that one because cool corridors aren’t just for large cities that have a lot of resources.

Q: Within communities, do certain populations tend to be more vulnerable to the impact of extreme heat and could cool corridors be a strategy for improving the quality of life in those areas?

A: Heat equity is a really important concept. Heat isn’t equitably distributed across the city. And unfortunately, vulnerable neighborhoods are often marginalized, lower-income, minority populations. There have been several studies that have shown that formerly “redlined” neighborhoods are much hotter than their richer counterparts, even to this day, by as much as 12 degrees. Cool corridors can help redress some of those inequities.

Q: Can you tell me about the work your team is doing in Tucson with the Cool Pavement Project?

A: It’s an evaluation of Tucson’s pilot Cool Pavement Program, and it’s funded by the U.S. Department of Transportation’s National Institute for Transportation and Communities. And so, myself, along with my research colleagues Kristina Currans and Nicole Iroz-Elardo, are partnering with the city [to evaluate] an asphalt rejuvenator that supposedly has heat-reduction benefits when it’s applied. The city applied this asphalt rejuvenator last December, and we’ve been taking measurements [of surface temperatures] and we’re doing the analysis right now.

Q: So what is cool pavement?

A: There are a lot of different types of cool pavements, so it’s not very well-defined because these are relatively new technologies. You may have seen the pictures of folks painting streets, like, literally white or lighter colors, like in Los Angeles or Phoenix. [Tucson’s project] is interesting because it’s an asphalt rejuvenator that contains different chemicals to reflect the sun, so it’s more like a sunscreen than a paint.

D.C. has one of the most intense urban heat islands in the U.S.

Q: What are you trying to find out?

A: The goal of the project is really to see if the asphalt rejuvenator actually does function well as a cool pavement treatment. We’re taking surface temperature readings all through the day and night to see if it reduces the heat gained through the day and if it reduces the heat emitted back from the road. Nighttime heat is incredibly dangerous, too. We’re also taking measurements to evaluate what pedestrians would feel if they were walking along this road.

Q: Are cool corridor projects expensive?

A: Because cool corridors are such an open concept with many applications, it depends on what you’re talking about. Is it just a few more trees? Is it increased bus shelters or shading along the road? Or is it a whole cool corridor with cool pavement? Certainly cool pavements and treatments can be more expensive. But as more cities adopt these, there is the possibility the prices will come down as they become more widely available.

Q: Is there anything else about the work you’re doing in this area that you’d like to mention?

A: One of the big-picture things is that our governance structures for heat are much further behind [how we manage] other climate risks. If you ask anyone about what transportation resilience looks like, a lot of times people look at flood resilience or resilience to hurricanes. My point is that we should consider heat resilience along with those other components.