What Does it Take to be Resilient?

Hurricane Michael damage on SR-30 (US-98) in Franklin County, Florida. Photo courtesy of Kevin Wall.

Resilience is a word that is now circulating amongst transportation agencies, industry, academics and policy makers. But what does this word mean, and what are the implications for the future of our roads?

The Federal Highway Administration defines resilience in FHWA Order 5520 as “the ability to anticipate, prepare for, and adapt to changing conditions and withstand, respond to and recover rapidly from disruptions.” It is no secret that our infrastructure has been tested, especially as it has aged. Just this past year alone, the U.S. experienced a record-breaking hurricane season with 30 named storms and 12 landfalling storms. On the west coast, California experienced the worst wildfire season in its modern history with the August Complex fire burning a swath of land estimated to be the size of Rhode Island. The middle of the country is no better off — in 2019, Iowa and Nebraska experienced the second 500-year flood in 10 years, putting many roads underwater. Other climate disruptions include drought and heavy precipitation, tornadoes, record breaking heat or cold like that experienced in Texas in 2021 and rapid temperature changes, all of which can have a detrimental impact on our pavements.

Resilience and the challenge it presents

One of the big challenges facing pavement infrastructure is flooding. Agencies have expressed concerns about flood inundation and its impact on pavement performance. Once a pavement base becomes saturated, pavement strength is reduced and materials may be compromised. This is already becoming problematic along the east coast due to sea level rise and storm surges. Another challenge is extreme temperature — temperature swings can cause rutting, cracking and buckling of pavements. Drought followed by heavy precipitation, especially in areas with expansive clay, can lead to major roadway deterioration. Further, while a disruption may directly impact a portion of pavement, cascading events can create indirect impacts on surrounding infrastructure such as excessive loading of overweight (but permitted) debris removal trucks on pavements after a tornado or hurricane or the rerouting of tractor trailers on local roads due to a main route being compromised by flood waters.

What now?

What are we to do with this predicament? We must adapt, and fortunately the resilience lexicon has a word for that: adaptation. FHWA Order 5520 defines adaptation as “an adjustment in natural or human systems in anticipation of or response to a changing environment in a way that effectively uses beneficial opportunities or reduces negative effects.” A non-infrastructure example is our collective resilience to the challenging work conditions presented to us this past year by the COVID-19 pandemic. While the world momentarily stopped, we couldn’t stay in “pause mode” forever. So, we adapted. One such adaptive strategy is the leveraging of web-based conferencing tools like Zoom, WebEx and the like. Not only do we meet microphone-to-microphone and camera-to-camera to discuss business, but we also virtually conduct educational coursework, webinars and even conferences. We adapt.

It is important to recognize there is no single adaptive strategy that will work for all situations. Decision makers and designers need to identify the key vulnerabilities of the highway, assess the risk of a disruption and then decide what adaptive strategies to employ. Often, the first thought is to “harden” or strengthen the infrastructure so that it is protected and can withstand nearly any disruption. This is a technically effective adaptation strategy, but it can also be cost prohibitive. Adaptation through modification is another approach that can be taken — using materials and techniques to harden the infrastructure to a certain degree while recognizing that the infrastructure has a potential to be disrupted. Another adaptive strategy is to simply accept and plan, meaning accepting that failure may occur, and developing plans now between agency and industry to rapidly repair the road. Finally, one can accept that it may make the most sense to abandon the route altogether, using alternative routes or relocating the community.

The tools we have, the tools we need.

The good news is asphalt pavements already have several resilient attributes and tools available, though we don’t usually think of them through the lens of resilience. For example, it is no secret that a benefit of asphalt is its rapid constructability. While usually considered a benefit for minimizing road closure, among other applications, if a roadway is compromised due to an earthquake or flood, asphalt can be used to rapidly repair the road so that people and goods can begin to move again. Asphalt is also 100% recyclable, which is particularly useful if aggregate or binder supply chains are disrupted by an event. Warm mix asphalt technology can be used not just for an environmental benefit, but also to pave in cold-weather response situations and to increase haul distances during a disruption. While asphalt materials are already adaptable to changing conditions like traffic, polymers and other binder or mixture additives can be used to add structure and manage climate variability.

Perpetual (long-life) pavement design is a method used to design a pavement thick enough to carry long-term structural loading without overdesigning, and it can be used for critical evacuation routes or potentially pavements that are subject to flood inundation. Standard maintenance overlays can also be leveraged by minimizing the amount of asphalt that needs to be milled, ultimately increasing the pavement structure’s thickness at approximately the same cost. Porous asphalt pavements are designed to handle water, making them a good option for managing large precipitation events. Deep rehabilitation methods such as full depth reclamation with an asphalt overlay are used to enhance the structural capacity of a highway at a reduced cost. This can also be done to harden roads that are now subject to flood inundation or potential rerouting of traffic. These are but a few of the tools we already have; we simply need to use “resilience thinking” to apply them as appropriate.

In conclusion, research efforts still need to find ways to incorporate future climate models into our design and material selection methods as opposed to the currently used historical climate data. Further, materials, pavement structures and new innovative adaptation strategies should be investigated to continue paving the way to a more resilient transportation infrastructure.

For more information on this topic, read the forthcoming NCAT Report 21-02, Asphalt Pavement: A Critically Important Aspect of Infrastructure Resiliency.

For more information about this article, please contact Ben Bowers.