Science & Technology

Phoenix Is Using Reflective Pavement to Combat Extreme Heat

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(Photo: City of Phoenix)
One of the country’s hottest cities is on a path to cooler temperatures—a reflective path, that is. In collaboration 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 the area’s notoriously toasty temperatures.

A study conducted by ASU’s Global Institute of Sustainability and Innovation, Healthy Urban Environments, and the Urban Climate Research Center revealed last year that pavement treated with CoolSeal retained less heat than traditional asphalt roads. The city selected chunks of eight different Phoenix neighborhoods and applied CoolSeal to areas already in need of pavement maintenance; then ASU’s researchers stepped in to monitor to the roads’ temperatures through thermal imaging (conducted during helicopter flyovers), sensors embedded in the pavement surface, and frequent drive-overs using a vehicle affixed 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, by accounting for 3D mean radiant temperature, air temperature, relative humidity, and wind speed and direction. 

The researchers found that by reflecting sunlight instead of absorbing it, cool pavement had the ability to reduce noon and afternoon hour temperatures (AKA the hottest time of day) by 10.5 to 12 degrees Fahrenheit. Though radiant temperature hovered at 5.5 degrees higher than air temperature due to the pavement’s reflectivity, this is on par with the experience of walking on concrete, meaning there shouldn’t be much of a temperature difference between walking on the treated street or the sidewalk. Sub-surface temperatures measured from cool pavement were also 4.8 degrees lower than that of traditional asphalt—a factor crucial to understanding the treatment’s longevity and effect on underlying, pre-existing pavement. 

Traditional asphalt temperature readings versus those of treated asphalt. (Image: City of Phoenix)

Though the Phoenix municipal government hasn’t squeegeed CoolSeal onto any new streets since the initial phase of the study, they’re considering the project a pilot program with opportunities for further research and development. According to the city’s website, researchers will continue to monitor how the reflective coating holds up and impacts temperatures for several years.

The cool pavement pilot program is a step in the right direction for a city plagued with heat-related concerns, from obscenely high electricity bills to rampant heatstroke. The City of Phoenix thinks cool pavement is a promising method of combating Phoenix’s status as a “heat island,” or an urban area with higher temperature than the areas around it. Though CoolSeal has been used in Los Angeles for a few years, its application is a little more exciting in a city where average summer temperatures linger in the triple digits. 

Though the gray pavement was a bit jarring to see the first time I witnessed it in action, CoolSeal’s “reflective” properties don’t result in visible glare and look just like a surface you’d see on a highway. Cool pavement also doesn’t make the roads too smooth, even in wet conditions (read: monsoon season). It might, however, prevent you from fulfilling the old adage about frying an egg on a sidewalk.

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