Painting city streets with a light-coloured, reflective coating can cool the asphalt underneath, but it can also increase heat exposure for people walking on the road. That unexpected trade-off emerged from a major trial in the American Southwest. In 2020, the City of Phoenix Street Transportation Department coated 36 miles of neighbourhood roads and a public parking lot with CoolSeal, a grey, water-based asphalt treatment designed to reduce the urban heat island effect. Researchers from Arizona State University (ASU) studied the treated roads for a year. Their findings showed that while the coating successfully lowered road temperatures, it also created a more complicated situation for pedestrian comfort and safety.
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