Phoenix uses reflective pavement to combat extreme heat

(Photo: City of Phoenix)
One of the hottest cities in the country is on its way to cooler temperatures i.e. a reflective path. In conjunction with Arizona State University, the City of Phoenix, AZ is applying a gray reflective coating, called CoolSeal, to residential streets in an effort to alleviate notoriously warm temperatures in areas.

A to study conducted by ASU’s Global Institute for Sustainability and Innovation, Healthy Urban Environments and Urban Climate Research Center revealed last year that pavement treated with CoolSeal retained less heat than asphalt roads traditional. The city selected pieces from eight different Phoenix neighborhoods and applied CoolSeal to areas already in need of pavement maintenance; then ASU researchers intervened to monitor the temperatures of the roads thanks to thermal imagery (carried out during helicopter overflights), sensors integrated into the surface of the roadway and frequent passages using a vehicle equipped with surface and air temperature readers. ASU even developed MaRTy, its own mobile weather station that measures radiant heat, or the human experience of heat, taking into account the 3D average radiant temperature, air temperature, relative humidity. and wind speed and direction.

Researchers found that by reflecting sunlight instead of absorbing it, cold pavement had the ability to reduce midday and afternoon temperatures (AKA, the hottest time of the day ) 10.5 to 12 degrees Fahrenheit. Although the radiant temperature hovered 5.5 degrees above the air temperature due to the reflectivity of the pavements, this is comparable to the experience of walking on concrete, which means it does not should not be much temperature difference between walking on the treated street or the sidewalk. Sub-surface temperatures measured from a cold pavement were also 4.8 degrees cooler than from traditional asphalt, a critical factor in understanding the longevity and effect of the treatments on the pre-existing underlying pavement.

Traditional asphalt temperature readings compared to treated asphalt. (Image: City of Phoenix)

Although the Phoenix municipal government has not introduced CoolSeal to new streets since the initial phase of the study, it sees the project as a pilot program with opportunities for further research and development. According to the city’s website, researchers will continue to monitor the behavior of the reflective coating and its impact on temperatures for several years.

The cold pavement pilot program is a step in the right direction for a city plagued by heat-related issues, from obscene electricity bills to rampant heatstroke. The City of Phoenix believes the cold pavement is a promising method to combat Phoenix’s status as a heat island or urban area with a higher temperature than the areas around it. While CoolSeal has been in use in Los Angeles for a few years, its application is a bit more exciting in a city where average summer temperatures linger by triple digits.

While the gray pavement was a bit shocking to see the first time I saw it in action, the reflective properties of CoolSeals do not cause visible glare and look like a surface you would see on a freeway. The cool pavement also doesn’t make the roads too slick, even in wet conditions (read: monsoon season). However, that might stop you from living the old adage about fried egg on a sidewalk.

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