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July 16, 2024

Q&A: The climate change toll on roads - two UW professors weigh in

Sarah McQuate

UW News

Two University of Washington researchers are investigating how to mitigate the effects of climate change on common road pavements, such as asphalt and concrete.Mark Stone/University of Washington

We mostly take roads for granted until something bad happens - a heatwave leads to a street buckling or an atmospheric river makes a neighborhood creek spill over its banks and flood our route to work.

As climate change brings about rising sea levels and more extreme weather, these issues with our roads are likely to be exacerbated. Two University of Washington researchers are investigating how to mitigate the effects of climate change on common road pavements, such as asphalt and concrete. Nara Almeida, assistant teaching professor in the School of Engineering & Technology at UW Tacoma, studies sustainable materials for pavement manufacturing. Stephen Muench, UW professor of civil and environmental engineering, studies how to make transportation infrastructure resilient.

UW News asked both to discuss the effects of climate change on roads and how their research addresses these issues.

Nara AlmeidaUniversity of Washington

What aspects of climate change affect roads?

Nara Almeida: There are several consequences of climate change that can affect the durability and longevity of roads. These include extreme temperatures, significant temperature fluctuations and floods.

It is important to note, however, that roads built today also contribute to climate change and its effects. Roads absorb a lot of solar radiation and contribute to the increase in surrounding temperatures. This phenomenon, known as the "heat island effect," can exacerbate climate change.

How does flooding impact roads?

Stephen Muench: There are two issues. The first involves a process called "scour," which is when water moves across a road and dislodges the pavement and underlying material, usually soil and rocks. Scour can be addressed by raising a roadway to above a new, higher anticipated flood depth or protecting it with levees and walls. Both options are expensive. Relocating the road is another option here, but that is also expensive and sometimes not possible.

Stephen MuenchUniversity of Washington

The second issue is that flooded roads are unusable and can be permanently weakened by flooding. This can occur because of extreme precipitation or sea level rise. Higher sea levels on average mean that the high tides - sometimes called "king tides" - may flood your road rather regularly. In places like Florida, where sea level rise is quite noticeable, we have seen some rather extreme measures put in place. For instance, Miami Beach has spent more than a decade raising its roads and installing backflow preventers and pumps to combat flooded neighborhoods and roads.

NA: Flooding on roads also leads to critical issues in the gravel and soil layers beneath the pavement surface layer. Extreme precipitation events can increase the moisture content in these layers, which makes the roads weaker and more flexible than they should be. Effective drainage systems can help these pavement layers regain their properties, but if flood events occur in quick succession, it could lead to permanent damage or failure.

How do extreme temperatures affect roads?

NA: For cold temperatures, there are a few issues. First, cold temperatures can make pavements that are meant to be flexible, such as asphalt, more likely to crack. Also, during freeze-thaw cycles, water inside the pavement expands when it freezes and contracts when it thaws. This phenomenon can accelerate deterioration, which leads to large cracks in rigid pavements, such as concrete, and potholes in flexible pavements, such as asphalt. Finally, deicer salts used in cold conditions can chemically react with pavement materials and deteriorate the pavement's structure over time.

SM: Another temperature issue that we typically notice here in Seattle is what happens during our increasingly common heat waves - say, three consecutive days of over 100 F weather. Infrastructure actually expands during hot weather, which can cause the edges of concrete pavement slabs to butt up and push on one another until the joint gives out and pops up to relieve stress.

NA: Some recent studies suggest that these damages tend to be worse if the concrete pavement has a thick surface layer and is subject to heavy loads, which is the case in our roadways.

Can you talk about how your research addresses these issues?

NA: One area I am particularly interested in is using what is called "pervious concrete" as the surface layer of pavement. These pavements absorb rainwater and recharge water tables, which could help with both flooding and the heat island effect.

Another indirect benefit of these pavements is that they could help filter contaminants in stormwater runoff. Right now, when it rains, water hits impermeable polluted surfaces, such as roofs and roads, and then it flows into lakes, rivers and other bodies of water. Pervious concrete could be really helpful in the Seattle and Tacoma region, where preserving aquatic wildlife, particularly salmon populations, tends to be a major issue.

I am also interested in using waste byproducts to manufacture pavements and other construction materials. One example is using water-treatment sludge and byproducts from the steel-production industry to make concrete.

SM: The industry buzzword for addressing climate change is "resilience." Here, this means the ability of roads exposed to hazards (such as flooding or extreme heat) to resist, absorb, accommodate or adapt - and then to recover in a timely manner.

Before I was a professor, I spent seven years in the U.S. Navy driving a nuclear submarine. We were always thinking about what could possibly go wrong and practicing our response to quickly and safely recover from it. It is harder to do this for an entire transportation network, but it has to be done. It is time we spent some serious effort on it. It is not practical to design a pavement to be resistant to everything. At some point, you have to admit that if a flood or other event is strong enough, you are just going to have to absorb damage and then recover. I want to know how to triage a system, and then recover quickly with what will surely be limited resources after a hazard event.

I am particularly interested in recovery after a major flooding event. We just started a project that addresses how flooding impacts the resiliency of pavement systems. Our current work in the National Cooperative Highway Research Program will provide guidance to state departments of transportation on how to quantify the effects of flooding and how to improve resilience.

What do you wish people understood about roads and climate change?

NA: The way our roads are currently built and used contributes to climate change. To reduce the embodied carbon footprint of road manufacturing, we need to reuse and recycle materials for road construction, hire local construction companies, buy from local suppliers and implement other sustainable strategies.

To address the operational carbon footprint, we need to rethink how we move within, to and from our cities. The transportation sector is the largest contributor to U.S. greenhouse gas emissions, so we need to live closer to where we work - and walk, bike and use public transportation more often. Of course, this responsibility isn't solely on us as citizens, and creating walkable cities with functional public transportation systems depends on political decisions.

SM: Resilience is so important to infrastructure today that it is at the core of our department's strategic plan: "Create a resilient and sustainable world." We build this idea into our teaching, and it forms the basis for a large amount of our research both in climate change adaptation, and as a response to natural hazards.

I think we have the technology and ability to address climate change with respect to pavements and a lot of other infrastructure. However, most of this adaptation will take effort and money. So, I think this is more a "people issue" than a technology issue. Specifically, are we, as a society, willing to spend money and time to address this?

For more information, contact Almeida at [email protected] and Muench at [email protected].

Tag(s): College of Engineering • Department of Civil & Environmental Engineering • Nara Almeida • Stephen Muench • UW Tacoma