Dark colored asphalt absorbs between 80 and 95 percent of the sun's rays, heating up not just the streets themselves but the entire surrounding area. When temperatures in Southern California rise above 100 degrees Fahrenheit, surface temperatures on asphalt roads can climb to 150. The EPA says the urban heat island effect can add up to 22 degrees Fahrenheit to the average air temperature in a city compared to the surrounding area. Los Angeles has more than 7,500 miles of roads covering the basin, turning the entire city into what one official described as an oven.
CoolSeal was originally designed by the military to keep spy planes cool and hide them from satellite infrared cameras. Engineers developed it for military air bases to keep aircraft cool while they rest on the tarmac, but someone realized the same material could work on civilian infrastructure. CoolSeal is an asphalt based sealant with an added cooling property that reflects more than 35 percent of sunlight, compared to traditional black pavement that absorbs and traps the sun's heat even after the sun sets.
The coating can reduce street temperatures by as much as 20 degrees Fahrenheit, though according to the Bureau of Street Services, LA streets rendered lighter in color with CoolSeal are 10 to 15 degrees cooler on average than streets that have not been treated. The difference is measurable immediately. Greg Spotts, assistant director of the Bureau of Street Services, demonstrated the effect by standing on untreated black asphalt that measured about 130 degrees Fahrenheit, then moving to the CoolSeal treated section. The temperature drop is significant enough that dogs have learned the coating is cooler on their paws and will walk away from crosswalks to stay on the grey sections.
Satellite thermal cameras show that the special cooling pavement not only lowers the temperature on the road but produces a cooler neighborhood in general. Buildings require less air conditioning. Energy costs drop. Los Angeles has heat related deaths even in the winter, according to Spotts, making the cooling effect genuinely lifesaving rather than just comfortable.
The project comes with a price tag of around $40,000 per lane mile. That's substantial money for what looks like paint, though the coating promises to help reduce road maintenance by slowing the rate at which asphalt breaks down from UV exposure. In 2015, as part of LA's Green New Deal, Mayor Eric Garcetti pledged to lower the city's average temperature by three degrees over the next 20 years. Companies like CoolSeal are set to add their coating to 200 blocks within the city as part of the Cool Streets LA initiative.
The pilot project covered one neighborhood street in each of LA's 15 council districts with CoolSeal. Since the pilot program, GuardTop has received inquiries from all over the world, including China, Israel, Australia and Saudi Arabia. The interest makes sense. Every major city deals with the heat island effect. Every city has miles of dark pavement baking in the sun. The solution isn't complex or futuristic. It's a coating that reflects light instead of absorbing it, borrowed from military hardware and applied to residential streets.
Spotts said his end goal is to have multiple solutions to lowering the temperature, noting that the pavement hasn't changed in 50 years. White streets won't solve urban heat alone, but combined with tree planting, cool roofs, and green spaces, the cumulative effect matters. Cities worldwide are watching because they have the same problem and limited options. Painting roads white sounds absurd until you measure the temperature difference and realize it works.