Cool pavement is a road surface that uses additives to reflect solar radiation unlike conventional dark pavement. Conventional dark pavements contribute to urban heat islands as they absorb 80–95% of sunlight and warm the local air. Cool pavements are made with different materials to increase albedo, thereby reflecting shortwave radiation 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." Existing dark pavement can be altered to increase albedo through whitetopping or by adding reflective coats and seals. New pavement can be constructed to increase albedo by using modified mixes, permeable pavements, 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 and air pollution. Lower temperatures would also slow chemical reactions that create smog. 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.
Improvement in water quality. Permeable pavements reduce stormwater runoff by allowing water to soak into the pavement and soil. Permeable pavements can reduce runoff by up to 90 percent. Reducing runoff minimizes sewer overflows and stream scouring. Permeable pavements also act as a filter, removing dust, dirt, and pollutants from the water before it seeps into the Earth's groundwater.
Increased quality of life. Lower temperatures reduce heat-related illnesses and illnesses from the formation of smog. Permeable pavements can "enhance safety because better drainage reduces water spray from moving vehicles, increases traction, and may improve visibility by draining water that increases glare."
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
Greater cost than dark pavement.
* According to the FHWA, the cost of porous pavement is approximately 10 to 15 percent higher than the cost of regular asphalt, and porous concrete is about 25 percent more expensive than regular concrete.
