Success Story: Cool Pavement
Raleigh curbs urban heat islands through pavement rejuvenation
Project Purpose
The City of Raleigh’s Transportation Department overlayed temperature data with street maps to see where roads might be contributing to high temperature areas. They sought a cost-effective solution to the continuing costs of road repair and the negative health effects of urban heat islands. City staff used a reflective coating that protects road surfaces from wear while reflecting heat.
Quick Facts
- The City of Raleigh’s Transportation Department mixed titanium dioxide into their pavement rejuvenator. By coating their road with this lighter color mixture, the City is slowing down wear and reflecting more solar energy, decreasing temperatures.
- The titanium dioxide mixture has a third benefit. It helps reduce pollution. The compound helps block pollutants that would have been released by the aging asphalt (Research Triangle Cleantech Cluster, 2022). In addition, the pavement coating reacts with vehicle exhaust and sunlight to convert the exhaust into less harmful substances – reducing air pollution.
- Summertime road temperatures can cool by 5-20 degrees F after a coating application. The Global Cool Cities Alliance’s Cool Roadways Partnership is currently testing the solution at larger scales in Phoenix, Ariz. and Los Angeles, Calif. (Global Cool Cities Alliance, 2022).
- In addition to cooling road surfaces, cool pavements can reduce energy needs for nearby indoor cooling.
What is an urban heat island?
Structures such as buildings, roads and other infrastructure absorb and re-emit the sun’s heat. These hard surfaces re-emit more heat than natural landscapes. Urban areas, where structures are highly concentrated and greenery is limited, become “islands” of higher temperatures relative to outlying areas. These pockets of heat are referred to as “heat islands.” Heat islands can form under a variety of conditions, including during the day or night, in small or large cities, in suburban areas, in northern or southern climates and in any season (EPA, 2014).
What is a pavement rejuvenator?
Roads made of asphalt break down and form cracks over time. Pavement rejuvenators are substances used to resurface roads that can restore asphalt conditions and prevent further break down.
The Raleigh Transportation Department used a product called A.R.A.-1 Ti, which combines a pavement rejuvenating agent with a titanium dioxide (TiO2) solution. The mixture protects the roads and helps reduce the heat island issue.
Spotlight on Equity
The impacts of rising temperatures are higher in underserved communities. People living in poorly insulated mobile homes, with limited access to air conditioning and who experience asthma and cardiovascular disease have a high risk of heat-related illness (EPA, 2014). To help address equity issues, local transportation departments could prioritize cooling roadways in parts of town that are home to high percentages of the community’s most vulnerable residents.
| Key Info | |
|---|---|
| Location | Raleigh, N.C. |
| Estimated Costs | ~$500,000 |
| Published | March 1, 2024 |
| Project Contact |
|---|
| Benjamin R. Griffin, PE Division Manager, Street Maintenance City of Raleigh Transportation Department Benjamin.Griffin@raleighnc.gov (919) 996-6903 |
| Related Resources |
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| See other efforts in Raleigh aimed at managing extreme heat. |
- In 2020, the City of Raleigh Transportation Department began looking for ways to curb the costs of pavement repair. Contractors proposed using a pavement rejuvenator.
- In 2020-21, the Transportation Department applied the solution to a selection of roads. They coated 150,000 square yards of roadway in the first year, focusing on roads three to six years of age.
- In 2021, the City worked with several area partners to study how summer temperatures varied across town. City residents collected temperature and other data throughout the day. Project partners recorded their results in an online heat island map.
- The Raleigh Transportation Department overlayed this heat data with street maps to see where roads might be contributing to high temperature areas. In response, Raleigh Transportation decided to focus its road upkeep efforts on areas with high heat.
- Cost for the pavement solution was around $2 per square yard. In 2022, the total cost for Raleigh was around between $500,000 and $600,000 to cover roughly 275,000 square yards of roadway.
- Raleigh provided funding through its Street Maintenance Capital Improvement Program.
City of Raleigh
- Pavement rejuvenation extended the life of asphalt pavement in the city. Staff anticipate fewer road-related costs, resources and labor-intensive work will be required in the future.
- Monitoring has shown positive results. The coating reduced heat absorption and increased solar reflection by nearly 400%, leading to lower late-evening road surface temperatures.
- Raleigh is scaling up the number of road coating applications each year.
- The trial run helped to showcase the benefits of pavement rejuvenating technology. Other communities are applying the same coating.
The project manager stated that the biggest update to the program from 2021 to 2022 was the integration of the heat island data. They used the maps to inform decisions about where to place the product. And rather than applying it citywide, they can now apply the coating where it will have the greatest benefit for residents.
There are several methods and products that assist with urban heat island mitigation. City of Raleigh staff recommend doing your research to select the one that provides the most benefit for your program. The coating they selected not only helped with road preservation, but they get the added benefits of reduced pollution and urban heat island mitigation from one product.
EPA. (2014, June 17). Heat Island Impacts. Retrieved from United State Environmental Protection Agency: https://www.epa.gov/heatislands/heat-island-impacts
EPA. (2014, June 17). Learn About Heat Islands. Retrieved from United States Environmental Protection Agency: https://www.epa.gov/heatislands/learn-about-heat-islands#heat-islands
Global Cool Cities Alliance. (2022, June). Cool Roadways Partnership. Retrieved from https://globalcoolcities.org/cool-roadways-partnership/
Research Triangle Cleantech Cluster. (2022, May). City of Raleigh's Pollution Remediation, Heat Island Reduction, and Pavement Preservation with TiO2 Enhanced Pavements. Retrieved from https://www.researchtrianglecleantech.org/award/city-of-raleighs-pollution-remediation-heat-island-reduction-and-pavement-preservation-with-tio2-enhanced-pavements/