U.S. is on the road to solving an urban environmental problem

Some U.S. cities are covering their asphalt roads with a coating that prevents the blacktop from absorbing and radiating the sun’s heat.

The pavement’s temperatures stay lower, which keeps air temperatures and air-conditioning bills for nearby buildings lower.

Cities especially might benefit from the innovation. They are hotter than rural areas because concrete, brick and dark roofs trap heat, creating “urban heat islands.”

Black asphalt can heat up to 65 Celsius on a hot day and radiate that heat long after sundown. Testers typically find a difference of 6 degrees Celsius between the coated pavement and nearby uncoated pavement, according to Greg Spotts, a local official in Los Angeles, one of the cities trying the method. At certain times of day in certain seasons, Spotts estimates the coating reduces a road’s temperature by as much as 11 degrees Celsius.

Two people in safety gear standing as a third spreads white liquid spilling from truck onto blacktop (Los Angeles Bureau of Street Services)
Workers apply heat-reflective coating to Beachy Avenue in Los Angeles. (Los Angeles Bureau of Street Services)

Scientists are working to develop a heavier-duty, heat-reflective asphalt slurry that can be used on highways. Los Angeles uses CoolSeal, a product durable enough for residential streets — a coat lasts from three to seven years according to a spokesman for GuardTop, the manufacturer — but not tough enough for major roads.

Encouraging innovation

A collaboration of local government, businesses and nonprofit organizations put the cool pavements project on the road.

The Los Angeles-based nonprofit organization Climate Resolve approached the city, and several departments picked up the idea. The project got valuable input from the Heat Island Group at Lawrence Berkeley National Laboratory, a Department of Energy lab managed by the University of California.

Other U.S. localities are testing solar panels that form a roadbed and generate electricity.

Spotts is hopeful that Los Angeles will spur new possibilities for the asphalt coating. Because of the city’s buying power, it can create a market, encouraging manufacturers to refine a product.

Painting pavement is a low-cost and low-tech solution that could work anywhere in the world. “There is a real opportunity here,” says David Fink of Climate Resolve.