Phoenix and the Valley continue to look for ways to reduce the impacts of extreme heat, and the state’s biggest city has been experimenting with cool pavement in an effort to do that. Officials say Phoenix has put the coating on more than 100 miles of roads since it started its program in 2020. The goal is to reflect heat away from the surface.
New research suggests the cool pavement is doing that — but it comes with trade-offs.
Jennifer Vanos, an associate professor in the School of Sustainability and the Global Futures Laboratory at ASU, largely focuses her research on understanding the exposures and impacts of extreme heat on humans. Vanos joined The Show to talk about the new data and her main takeaways from this most recent research.
Full conversation
MARK BRODIE: Phoenix and the valley continue to look for ways to reduce the impacts of extreme heat and the state's biggest city has been experimenting with cool pavement in an effort to do that. Officials say Phoenix has put the coating on more than 100 miles of roads since it started its program in 2020.
The goal is to reflect heat away from the surface. New research suggests the cool pavement is doing that but it comes with tradeoffs.
Jennifer Vanos is an associate professor in the School of Sustainability and the Global Futures Laboratory at ASU. Her research largely focuses on understanding the exposures and impacts of extreme heat on humans.She joins me to talk about this new data and Jennifer what to you are the main takeaways from this most recent research?
JENNIFER VANOS: Yeah, there's so many things that we have been testing and want to continue to test on the Cool Pavement Pilot Program with the city of Phoenix.
Some of the newer data we collected that stood out to me was looking at the UV reflectance and we learned that there is no additional UV. So ultraviolet radiation reflection from these cool pavement surfaces compared to something like asphalt or concrete.
So that was good to see, as it's a concern that many people bring up. We also tested a couple of different types of surfaces and found not too large of differences between them in terms of the products that the city of Phoenix is thinking about using in the future. And I think what's promising to us also is that some of the phase one results that we tested from 2020 we were able to find the exact same results which being able to repeat experiments and find the same data provides more robust results to the city and to other end users.
BRODIE: Yeah, I wanted to ask you about that because it seems as though some of what you found now really corresponds with what you have found in the past.
VANOS: Yes, yes. And so being able to have that repeated data collected and, and find very similar results in terms of performance gives us more confidence in in what we're finding on the surface above the surface and so forth in terms of the potential positive impacts or tradeoffs that we might need to understand as we think about applying these kinds of technologies in the real world.
BRODIE: Well, so let's talk about at least one of those tradeoffs, which is that the data has been showing now that while the cool pavement does reduce the temperature of the surface, it actually can make things warmer for people who are standing on it. Like, if you're walking across a street that has cool pavement on it, it will feel a little bit warmer to you than it would otherwise. So I'm curious how you use that data? Like, what does that tell you in terms of maybe the kind of material used or maybe the way in which this cool pavement should be used?
VANOS: Yeah, it, it's, it's a really great question and it's an important consideration when we think about where we apply cool pavement. What it does indicate to us is that in the middle of the day as a person, if a person is standing on the surface, there is a high reflection from the surface, but that indicates to us that the, the pavement is working how it's supposed to, right? It's supposed to reflect more sunlight back out, but that sunlight is supposed to escape the urban environment and not hit buildings or people.
And so this is a necessary trade off of the way this technology works. Now, what I would say is that, we don't want people walking in the middle of roads and our results show that there's no difference in exposures if someone is walking on a sidewalk next to one of these,, coded roadways, especially a sidewalk that is shaded.
And then second, it tells us where would be optimal or sub optimal locations for putting this. So we really don't want to be putting it in places where there's a lot of foot, foot traffic middle of the day. And that's where we see these differences.
So we wouldn't want to be putting this in places like parks or playgrounds or plazas where we expect to have more foot traffic in the middle of the day throughout the year because it can, increase that overall total heat burden on a person which radiation, especially in the desert is, is a large component of that.
BRODIE: I wonder if there's maybe for lack of a better word, sort of a branding or a pr problem that we have with cool pavement in the sense that people maybe think that it is capable of doing things that it isn't. And I ask because, you know, you talk about this and I think for a lot of folks who think, oh, great, it's gonna make everything feel cooler when, as, as you've discussed, that's not really what it's meant to do overall.
VANOS: Yeah, it, it is really interesting to think about this and even the perception of what feels cooler to people because we often just think about air temperature. But what increases our overall heat load the most in a place like Phoenix is that sun that exposure to the sun.
And it, it really can, can make us think about what are the most appropriate or effective heat mitigation strategies for a place like Phoenix that does have a lot of sun exposure and high air temperature. And, and the best way here to reduce our overall heat burden in the summertime is to reduce sun exposure.
One of the largest benefits of this technology that needs to be monitored over the long term is just that subsurface temperature reduction and how that may be helping sustain the pavement over a longer period and thus result in less maintenance needs to seal it again, to replace the entire street again over the long term. So that the city is really hopeful that they don't have to do as much of that spending on the update of the streets so often.
BRODIE: So it kind of also serves as a like almost a protective coating for the road underneath.
VANOS: Yes. And I think that's where we're seeing the greatest benefits. We don't talk about it as much, but we see pretty large decreases, of course, in the surface temperature, but it's in that radiation that it's not the heat is not getting to the sub surfaces either which is supporting less thermal expansion, which helps lengthen, it should help lengthen the lifespan of the road.
BRODIE: Is there research or or development going on in terms of trying to refine the surface or maybe change it up in, in some way to try to improve on the results?
VANOS: Definitely actually from our 2020 phase one results with the city of Phoenix, the company we work with guard top, created what's called a Phoenix, a Cool Seal 2.0 or the Phoenix Gray because of some of the input from the residents actually and saying they didn't like how light or white it looked and you could see so much more, like oil and, and dirt on it. They wanted it to look more like a pavement or concrete.
So the company created a Phoenix gray which still has the performance in terms of reflection as the initial Cool Seal 1.0, but looks more like your traditional pavement. And so that's really good to see.
One of the things I really try to do is use our results from the fields to push industry to innovate more and more in this space because I feel like there's so much more that can be done.
BRODIE: So what then is next in terms of research? Like what do you want to find out next? What do you feel like maybe you need to find out next?
VANOS: We really need to see the long term benefits if they and what they are, if they exist to what extent. So we need to be looking at what is that difference in the long term surface temperature subsurface temperature reflectivity of these surfaces compared to the traditional coatings that are used that are lower costs.
And if we can be monitoring those long term changes over time and start to see the benefits, we can put some economic assessment on that and, and really be able to say, especially to the taxpayers, like where is the benefit coming from with these codings?
