Extreme heat driven by fossil fuels and deforestation is a global four-alarm fire. Land and sea temperatures continue to break all-time records month after month, year after year. Cities, thanks to the density of heat-trapping cement and asphalt and reduced green space, can be more than 10 degrees hotter than leafier suburban areas. That’s a big deal as the planet moves into heat readings beyond anything modern humans have witnessed.
One approach to mitigation involves road sealants that reflect more of the sun’s heat before it is absorbed by the streets. Shimmery street coatings are popping up across the United States, including several Texas cities like Dallas, Austin, and San Antonio.
One Dallas resident told KXAS that the cool pavement made it more comfortable to walk in his neighborhood.
But the published research, including an examination by Deceleration, suggests just the opposite.
Researchers studying a “cool pavement” pilot program in Los Angeles, Calif., found that reflecting the sun’s heat off the streets was causing pedestrians to contend with much hotter temperatures over the sidewalks. Arizona-based researchers suggest not applying such treatments in areas of high foot traffic, according to Bloomberg.
San Antonio led the way in “cool pavement” in Texas, with applications as early as 2021.
Results of the early pilot were not released to the public, said Jeannine Pyle, project manager at San Antonio Public Works Department, because the effort was poorly organized.
“The streets were, I don’t know how to put this nicely. It was kind of haphazard,” Pyle told Deceleration. “It was put together quickly. Council made the final decision.”
This summer, Deceleration examined one section of treated roadway, Clifton Forge Street in front of Shirley J. Howsman Elementary School on San Antonio’s Northwest side. We found lower temps on the street surface, as expected, but also a increase in temperature above the sidewalk adjacent to the treated roadway as compared to the sidewalk beside the untreated roadway.
Today, a better structured $5M pilot is ongoing in San Antonio, Pyle said, with interest in how to stack potential benefits, including combining “cool pavement” with “cool roofs” (that is, more reflective roofs, as in the Under One Roof program). The City of San Antonio is largely targeting neighborhoods being impacted by extreme heat but where homeowners and renters don’t have the resources to make heat-mitigating improvements for themselves.
“Cities are still learning about the impact of cool pavement and how best to deploy it,” Doug Melnick, San Antonio’s chief sustainability officer, wrote Deceleration. “We are rolling it out carefully and targeting very specific areas based on heat and equity indicators, and continuing to conduct research.”
Melnick said the “cool pavement” program was “one tool in our toolbox” that should be incorporated in what he described as “a broad heat mitigation strategy.”
He shared a study from Phoenix in which researchers reported that while “surface temperature reductions were strong, air temperature reductions were minor.”
He also forwarded to Deceleration an unreleased UTSA study.
On the subject of increased air temperatures caused by cool pavement treatment, the report authors found:
“When considering all the sites and times collectively, the average difference in the mean air temperature between the cool pavement sites and control sites was 0.07°F (i.e., the cool pavement sites were marginally warmer). This suggests that the potential cooling influence of the cool pavements did not outweigh other environmental factors such as atmospheric mixing.”
The hunt now is to find the materials that can both reflect heat from the sun while minimizing this spillover heat. The City is studying several pavement treatments, including GuardTop, PaveTech, GAF and SealMaster, to roadways in all 10 City Council Districts. This time around round results will be reported back to the public, Pyle said.
“UTSA is vetting the projects and is coming out with a to-be-published report on whether the cost-to-value is worth the heat mitigation,” Pyle said.
Residents can expect that report back by summer 2026.
