The results of a year-long pilot project that tested the efficiency of cool pavement, a water-based asphalt treatment that reflects heat instead of retaining it, were announced last week by the City of Phoenix Street and Transportation Department.
In partnership with Arizona State University scientists and the Phoenix Office of Sustainability, the department concluded that the pavement effectively lowered city temperatures and will potentially decrease energy consumption in Phoenix.
Cool pavement is a surface treatment compatible with traditional asphalt and is largely composed of water, soap, mineral fillers, asphalt and other recycled materials. Its lighter color absorbs less heat while the high reflectivity increases solar energy, making cool pavement environmentally sustainable for one of the fastest-growing cities in the nation.
“With all of this growth, one of the big things that we’re concerned with is heat resilience,” Director of the Street and Transportation Department Kini Knudson said. “We have a growing urban heat island issue, and we wanted to make sure we have ways to be able to address that.”
The heat island effect occurs when heat is absorbed by the pavement in a densely populated urban area, ultimately causing temperatures to rise. With Phoenix being the fifth largest city in the U.S., the cool pavement study served as an innovative way to combat the heat island effect and lower nighttime temperatures.
“The vision is actually for Phoenix to be the most sustainable desert city on the planet. We’re really focusing on that desert aspect and certainly around heat,” said Chief Sustainability Officer Mark Hartman.
The pilot project was conducted in one local park and sections of eight different neighborhoods across the city, encompassing around 36 miles of residential roads, according to Phoenix Special Project Administrator Rubben Lolly. The selection of these roads was largely based on pavement condition and geographical location.
Jennifer Vanos, co-lead of the project and assistant professor at the Arizona State University School of Sustainability, reported that on average, cool pavement ranged from 10.5 to 12 degrees cooler than regular asphalt during afternoon hours. The air temperature surrounding the pavement also decreased by 0.5 degree at night and 0.3 degree during the day. While these numbers seem low, air from parts of the neighborhoods that were not involved with the pilot project could have mixed in with the parts that were involved, Vanos said.
While cool pavement may be new to Phoenix, the asphalt treatment was implemented in Los Angeles before the Phoenix pilot project began. Like Phoenix, Los Angeles reported many positive features of the pavement, including a decrease in roadway surface temperatures.
Along with reducing temperatures, cool pavement is also financially beneficial. It is relatively the same price as regular asphalt, and with the sustainability and heat reduction it provides the city, the benefits are extremely prevalent, according to Lolly.
“Because the surface is so much cooler, it actually increases durability and will make it more economic than traditional coatings,” Hartman said. “It would really be impactful citywide.”
Looking toward the future, the city is excited to continue the investigation of cool pavement and plans to install it in more residential areas. Citizens involved in the pilot program showed support for the pavement and are eager to see its growth within the city.
“When we are ready to expand this program, I am anticipating that we’ll have people lined up to be able to receive this pavement treatment,” Knudson said. “We’re excited about its future, and we’re excited about our residents being excited about it as well.”
Contact the reporter at easchaib@asu.edu
