On a hot Texas afternoon, asphalt can become significantly hotter than the air above it. Roads and parking lots absorb solar energy throughout the day and release some of that stored heat later, contributing to the urban heat island effect.
One proposed solution is “cool pavement,” a lighter-colored or reflective pavement designed to absorb less solar energy. Cities including Phoenix and San Antonio have been testing the technology, and the results offer both promise and reasons for caution.
How Does Cool Pavement Work?
Reflective cool pavements use lighter-colored materials or surface coatings to reflect more sunlight rather than absorbing it as heat. Other approaches include permeable pavements that allow water to pass through and potentially provide cooling through evaporation. The concept works at the pavement level. Phoenix researchers found reflective treatments reduced midday and afternoon pavement surface temperatures by approximately 10.5 to 12 degrees Fahrenheit compared with conventional pavement. San Antonio testing also found some treatments lowered afternoon pavement temperatures.
But cooler pavement does not necessarily mean cooler people. Research in San Antonio found the effect on surrounding air temperature was modest and generally too small to conclusively attribute to the pavement.
“There is no evidence that the air is significantly cooler at approximately six feet above the surface,” said Gary D. Nicholls, P.E., Executive VP at Westward. “That’s an important distinction when we’re evaluating whether a technology is actually reducing the heat people experience.”
Looking Beyond Temperature
Nicholls says pavement performance also needs to be part of the conversation.
“An enormous amount of science, testing and engineering goes into asphalt pavement,” he said. “Road surfaces are designed not only for durability, but for safety, including providing the friction necessary for vehicles to stop effectively. When you add a coating to that engineered surface, those performance characteristics need to be carefully evaluated.”
There are other questions as well. Asphalt is highly recyclable: existing pavement can be milled, processed and incorporated into new pavement. Engineers will need to understand whether some reflective surface treatments could affect that recycling process.
Nicholls also points to the potential for highly reflective surfaces to contribute to nighttime light reflection in urban areas, as well as questions about long-term durability and maintenance.
A Tool Worth Testing
None of this means cool pavement should be dismissed. Testing new technologies under real-world conditions is how engineers determine what works. The evidence so far suggests certain cool pavements can meaningfully reduce surface temperatures. What remains less certain is how much that translates into lower air temperatures and improved comfort at the pedestrian and neighborhood level.
“It’s good to see cities testing these ideas,” Nicholls said. “But changes to something as important as roadway pavement need to demonstrate a meaningful benefit while still meeting the standards we expect for safety, durability and long-term performance.”
For now, cool pavement may be best viewed not as a silver bullet for urban heat, but as one potential tool that still has more to prove.