Among the most interesting exhibitors at the Greenbuild International Conference and Expo this week in Los Angeles (.. and okay, the virtual reality experience from the View glass people is pretty wild) may be the Asphalt Pavement Alliance challenging what we thought we knew about urban heat island effect with peer reviewed research from Arizona State University.

The term “heat island” describes urban areas that are hotter than nearby rural areas. The research from ASU calls into question many common assumptions about the ability of reflective pavements to mitigate urban heat island effect.

Reflective surfaces redirect solar energy and for this reason high albedo, reflective, or “cool” roofs have been suggested as an important tool for urban heat island effect mitigation. However, efforts to apply the same principle to non roof hardscapes, including 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,” 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Center of Excellence for SMART Innovations, pulls together research from around the world, including previously unpublished data from the team’s field research, that demonstrates the limits and side effects of relying upon reflectivity to reduce urban heat island effect.

Specific issues that may challenge what you think you know include increased cooling loads (and energy costs) for buildings subjected to solar reflections, increased light pollution from illumination at nighttime, increased wintertime snow and ice buildup even with additional deicing salts, and even human health concerns from UV radiation to visual glare.

“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.

Two respected research teams are currently performing separate pavement albedo research projects that are expected to be published within the next year. The first, a study funded by the California Department of Transportation at Lawrence Berkeley National Laboratory, in conjunction with the University of California, Davis, is looking at the impact of pavement albedo as a UHI mitigation strategy. And the second, the National Center for Asphalt Technology at Auburn University, in conjunction with Iowa State University National Concrete Pavement Technology Center, is conducting a pavement albedo aging study funded by the Federal Highway Administration.

In its adoption process for the upcoming version of Green Globes, the GBC Consensus Committee is proposing removing the urban heat island requirements for other than roof hardscape.

Given the growing body of evidence of unintended consequences associated with reflective pavements and the potential negative impact they may have on energy usage, it is time the drafters of other green building standards, rating systems and codes reevaluate the science and be prepared to eliminate provisions, including credits for urban heat island effect mitigation based solely upon a pavement’s reflectivity.

Read the report yourself at