Dedicated to providing knowledge, the Pavement Research Center uses innovative
research and sound engineering
principles to improve pavement structures, materials, and technologies.

NEWS

  • APT2012, the 4th International Conference on Accelerated Pavement Testing, will be held in Davis, California, in September 2012. Information and registration are available here.
  • Lifecycle Analysis Framework Kick-off Workshop held at UCPRC, May 2010. More information is available here.

Summer and Fall 2012 UCPRC Activities

Cooler Pavements. Commonplace paved features of urban areas, which include streets, parking areas, sidewalks, plazas, and playgrounds, typically cover a significant percentage of a city’s overall land area. For example, a study of Sacramento, California in 2000 estimated that roughly 39 percent of the city’s urban land area was covered in pavements when seen from above the vegetative canopy [1]. The thermal characteristics of these paved surfaces—their albedo, heat capacity, conductivity—and their interaction with solar radiation are among a number of causal factors that affect a phenomenon referred to as “urban heat island” (UHI). (Other factors affecting UHI include the area’s population and population density, its building materials, the spacing and height of buildings, waste heat generated by vehicles and building equipment, vegetative cover, and geographic location [2].)

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UHIs can be broken into two distinct types: surface heat islands and atmospheric heat islands. A surface UHI is defined as the increased temperature of exposed urban surfaces heated above the ambient air temperature [2]. An atmospheric UHI is the increased air temperature of an urban area compared to the surrounding rural area [2]. By extending these phenomena, a third type of UHI called “near-surface heat island,“ could be defined as the increased air temperature above the ambient air temperature at a greater height above the surface.

Depending on characteristics of an urban area, all three UHI types can have important consequences for city dwellers. Atmospheric UHIs can potentially cause poor air quality, increased energy consumption, and have other negative effects. Surface and near-surface UHIs can potentially affect human thermal comfort, air quality, and the energy use of nearby vehicles and buildings.

So-called “cool pavements,” which reduce urban heat islands, could potentially help mitigate heat island effects and reduce their negative impacts, but use of these alternative pavements does not guarantee benefits. How beneficial they are depends in part on the size and characteristics of the urban area and climate region, the extent and behavioral characteristics of air conditioner use, the materials and construction impacts of different pavement types, and a number of other considerations. Cost must also be considered and compared with other alternatives for addressing problems associated with UHI. Finding the answers to questions about when and where, and what kinds of cool pavements can provide how much net positive impact over the entire lifetime of pavements is an area requiring research.

With funding from the University of California, Davis Sustainable Transportation Center (through the University Transportation Centers program funded by Caltrans and the US DOT) and additional support from Caltrans, the UCPRC has undertaken a research investigation that has two goals: (a) to explore and evaluate the effectiveness and applicability of several cool pavement technologies and strategies, and (b) to quantify the environmental impacts of these cool pavements as they might occur in several urban climate regions in California, focusing on the near-surface heat island environment, which affects humans and vehicles on the pavement and nearby buildings. These results will also provide input for future investigations of atmospheric heat island.

In conducting this doctoral research study, a UCPRC graduate student is completing tasks in five main areas:

  • Laboratory testing of thermal properties of pavement materials.
  • Field measurement of the thermal performance of different cool pavement technologies and strategies, using both controlled test sections and uncontrolled existing pavements.
  • Development, validation, and application of local microclimate models in order to evaluate the lifetime impacts of varying cool pavement types in different climates.
  • Assessment of the impacts of cool pavements on (a) human thermal comfort and (b) energy use by air conditioning of vehicles and buildings during peak demand for the selected urban areas in three climate regions.
  • Development of a framework for consideration of near-surface heat island in Life Cycle Assessment (LCA) studies to examine the environmental impacts of cool pavements.

Three primary types of pavement are being investigated: concrete, asphalt, and integrated concrete pavers (concrete blocks). Within each of these three types, traditional impermeable pavements are being used as controls for comparison with one or more types of fully permeable pavement, which may provide cooling benefits through evaporation of water stored in them on hot days.

It is expected that the completed study (projected for completion by early 2013) will yield insights into whether and how cool pavement technologies and strategies may be deployed most advantageously. The research program will potentially provide a greater understanding of these pavements’ thermal behavior and their impact on local microclimates, as well as their life cycle effects on the broader environment.

Footnotes:

  1. Akbari H., Rose L., and Taha H. 1999. Characterizing the fabric of the urban environment: A case study of Sacramento, California. Lawrence Berkeley National Laboratory: Berkeley, CA.
  2. Navigant Consulting, Inc. 2011. Building technologies program, assessment of international urban heat island research - literature review of international studies on urban heat island countermeasures. Draft report Office of Energy Efficiency and Renewable Energy: USDOE: Washington, DC.


Important Note for Caltrans Users: Prior to scheduling pavement preservation (preventive maintenance or CAPM) or roadway rehabilitation work on flexible pavement highway sections, the District Materials Engineer and/or the Project Manager should review this spreadsheet to ensure that the proposed project does not include sections active in the “Quieter Pavement Research” (QPR) testing program. If the proposed project is within a QPR test section, please contact Linus Motumah of the Caltrans Office of Pavement Design before scheduling the work.

To view maps that show where the sections are located, click the following link: http://maps.google.com/maps?q=http://www.ucprc.ucdavis.edu/qpsectionsmap.kmz (or copy-and-paste it into a new browser window for a slightly larger view).

For more information, contact John Harvey of the UCPRC or Linus Motumah.