Cool pavement is a road surface that uses additives to reflect solar radiation unlike conventional dark pavement. Conventional dark pavements contribute to

urban heat island An urban heat island (UHI) is an urban or metropolitan area that is significantly warmer than its surrounding rural areas due to human activities. The temperature difference is usually larger at night than during the day, and is most apparen ...

s as they absorb 80–95% of sunlight and warm the local air. Cool pavements are made with different materials to increase

albedo Albedo (; ) is the measure of the diffuse reflection of sunlight, solar radiation out of the total solar radiation and measured on a scale from 0, corresponding to a black body that absorbs all incident radiation, to 1, corresponding to a body ...

, thereby reflecting

shortwave radiation Shortwave radiation (SW) is radiant energy with wavelengths in the visible (VIS), near-ultraviolet (UV), and near-infrared (NIR) spectra. There is no standard cut-off for the near-infrared range; therefore, the shortwave radiation range is also v ...

out of the atmosphere. Increasing albedo reduces heat transfer to the surface and can hypothetically cause local cooling if the spatial scale of the albedo reduction is sufficiently large. The EPA reports "that if pavement reflectance throughout a city were increased from 10 to 35 percent, the air temperature could potentially be reduced by 1°F (0.6°C)."U.S. Environmental Protection Agency. 2012.
Cool Pavements
In: Reducing Urban Heat Islands: Compendium of Strategies. Draft. . Existing dark pavement can be altered to increase albedo through

whitetopping Whitetopping is the covering of an existing asphalt pavement with a layer of Portland cement concrete. Whitetopping is divided into types depending on the thickness of the concrete layer and whether the layer is bonded to the asphalt substrate. Unbo ...

or by adding reflective coats and seals. New pavement can be constructed to increase albedo by using modified mixes,

permeable pavement Permeable paving surfaces are made of either a porous material that enables stormwater to flow through it or nonporous blocks spaced so that water can flow between the gaps. Permeable paving can also include a variety of surfacing techniques ...

s, and vegetated pavements.

Benefits

* Reduction in energy usage. Energy usage is reduced as local temperatures are cooled. Lower temperatures allow air conditioners to cool buildings with less energy. Temperature reductions attributed to increased pavement albedo in Los Angeles resulted in over $90 million per year in savings. Reflective pavement also reduces energy at night as they demand lower street light usage. * Improvement in air quality. A reduction in energy usage would lower

greenhouse emissions Greenhouse gas emissions from human activities strengthen the greenhouse effect, contributing to climate change. Most is carbon dioxide from burning fossil fuels: coal, oil, and natural gas. The largest emitters include coal in China and la ...

and air pollution (dependent on electric power fuel mix). Lower temperatures would also slow chemical reactions that create

smog Smog, or smoke fog, is a type of intense air pollution. The word "smog" was coined in the early 20th century, and is a portmanteau of the words ''smoke'' and '' fog'' to refer to smoky fog due to its opacity, and odor. The word was then inte ...

. In 2007, Surabi Menon and Hashem Akbari estimated that an increase of global pavement albedo of 35 to 39 percent could reduce carbon dioxide emissions worth about $400 billion.

Drawbacks

* Brightness. Cool pavement reflects much more light into the eyes of drivers, thus having the potential to temporarily blind them. * Considerable variation in unit price. Cool pavement costs vary as a result of numerous factors: ** Geographical region ** Local climate ** Labor contractors ** Time of year ** Site accessibility ** Underlying soils ** Project size ** Expected traffic ** The desired life of the pavement

References

{{reflist Pavements

Benefits

Drawbacks

See also

References