A 21-month field study of reflective pavement across 11,500 square meters in north Phoenix tracked what happened after the city coated roads with a lighter surface meant to cool the urban heat island. After dark, it delivered: air temperature dropped up to 0.58°C. In a city where nights at or above 90°F have tripled since 2019, that matters to anyone trying to sleep through them.
At midday, the cost fell on the people walking. The lighter surface bounced sunlight upward into their bodies, and a 2023 ASU study measured radiant heat exposure 4.5 to 5.8 degrees higher over reflective pavement than conventional asphalt at peak sun. An air thermometer reads slightly cooler, but a person standing on the street absorbs more heat than they would on untreated road.
Over 21 months, the surface itself degraded. Reflectivity dropped 53%, from 0.28 to 0.13, approaching the reflectance of the old asphalt underneath. Phoenix paused the program in 2024, citing product issues, and has since switched coatings. The city has treated more than 140 miles of road. A resident who'd lived with the surface for years told InvestigateTV: "I don't know that I really noticed a difference."
Before sunrise: No measurable difference between treated and untreated surfaces.
Midday: Air cools slightly, but reflected sunlight raises radiant heat absorbed by a pedestrian 4.5–5.8°F above conventional asphalt.
Evening and overnight: Air temperature reduced up to 0.58°C. Surface releases stored heat faster than conventional asphalt.
Degradation: Steepest reflectivity loss occurs in the first year. By month 21, surface approaches the albedo of aged conventional asphalt.
Best conditions: Low-traffic residential streets, open sky, no tall buildings. Researchers say reflective pavement cannot replace shade trees for pedestrian cooling.
Worst conditions: Downtown canyons where buildings block the sunlight the surface needs, pedestrian corridors, high-traffic roads where wear accelerates degradation.
Cost: Phoenix reports the reflective coating runs three times the price of conventional seal coating.