NAPA National Asphalt Pavement Association

Reflective Pavements May Not Reduce Urban Heat

Addressing the urban heat island effect (UHI) is a growing concern for many municipalities, but a new report from Arizona State University (ASU) calls into question many common assumptions about the ability of reflective pavements to mitigate UHI.

Reflective surfaces redirect solar energy and for this reason high-albedo, reflective, or “cool” roofs have been suggested as an important tool for UHI mitigation. However, efforts to apply the same principle to pavements overlook the complexities of urban geography and how ground-level reflections interact with pedestrians, vehicles, and the built environment.

The report, “Unintended Consequences: A Research Synthesis Examining the Use of Reflective Pavements to Mitigate the Urban Heat Island Effect,” surveys a wide range of recently published research into what happens to the energy redirected by reflective pavements. Specific areas of concern identified include increased energy demands for buildings subjected to solar reflections, increased light pollution, increased wintertime snow and ice buildup, and even human health concerns.

“Unfortunately, efforts to promote reflective pavements have moved more quickly than the scientific and engineering research. As this report indicates, reflective pavements may cool a pavement’s surface but there can also be negative environmental and social impacts on the areas adjacent to the pavement,” said Heather Dylla, Ph.D., Director of Sustainable Engineering for the National Asphalt Association (NAPA). “We cannot assume that reflective pavements will behave the same as reflective roofs. When energy is reflected from a ground surface, it doesn’t return directly to the sky. It reflects back at buildings and pedestrians. Heat concentration in urban areas is a multifaceted problem; it requires a solution that looks at more than just one mitigation strategy.”

The ASU report, authored by Jiachuan Yang, Zhihua Wang, Ph.D., and Kamil E. Kaloush, Ph.D., P.E., of the ASU National Center of Excellence for SMART Innovations, pulls together research from around the world, including previously unpublished data from the team’s field research, that demonstrates the limits and side effects of relying upon reflectivity to reduce UHI.

Given the growing body of evidence of unintended consequences associated with reflective pavements and the potential negative impact they may have on energy usage, NAPA is urging developers of green construction codes to eliminate any provisions that offer credits for UHI mitigation based solely upon a pavement’s reflectivity.

A copy of the report can be downloaded from the ASU National Center for SMART Innovations website at http://ncesmart.asu.edu/news/unintended-consequences.

NAPA representatives will be at the Asphalt Pavement Alliance booth (#3216) to discuss asphalt pavements, porous asphalt, urban heat island, and other issues during the Greenbuild International Conference and Expo, Nov. 20–21, in Philadelphia

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