Cities Painting Streets to Cool Down
As this summer’s heat affects wide swaths of the country, cities like Phoenix and Los Angeles have continued their efforts to coat their roads with a reflective grey paint to fight the intense heat waves.
According to reports, the use of cool pavement is, on average, 4.8 degrees cooler than traditional asphalt and, when the sun is at its most intense, can average 10.5-12 degrees lower in surface temperature.
?? NEWS: Three years after launching our Cool Pavement program, we've installed over 100 miles of cool coating across Phoenix!— Mayor Kate Gallego (@MayorGallego) June 6, 2023
This innovative coating is produced locally and is proven to reduce street surface temperatures by up to 12 degrees! ?? pic.twitter.com/XLqoX3AkjM
'Cool Pavement' Coatings Background
In November 2020, the Phoenix Street Transportation Department reported that it was nearing the completion of a series of “cool pavement” coating applications around the city.
The cool pavement treatments were a part of the city’s pilot program, where a team at Arizona State University studied the pavement coatings' possible impact regarding the area’s heat island effect over the course of several years. The idea for the pilot study was launched following a ASU-led study on solar reflective coatings back in July 2019. For the study, ASU researchers took two mobile biometeorological instrument platforms (MaRTy 1 and MaRTy 2) to Los Angeles in order to read how the city’s streets affected radiant heat and ultimately, pedestrians’ comfort.
The study was the first to measure the thermal performance of solar reflective coatings using instruments that sense meteorological variables relevant to a pedestrian’s experience: radiant heat, ambient temperature, wind and humidity.
In developing the Cool Pavement Pilot Program from the study, the City of Phoenix Street Transportation Department selected portions of eight neighborhoods and one city park to receive cool pavement treatment as part of the project. The portions cover 36 street miles at a cost of $3.3 million, which has come from the city’s street maintenance budget.
The nine areas chosen as they were already due for resurfacing and money would have gone toward rehabilitating those areas regardless of the material used, reported David Sailor, director of the Arizona State Urban Climate Research Center.
However, instead of using the reflective solar coatings like in Los Angeles, the city announced that it would be using cool pavement technology, CoolSeal, developed by California-based GuardTop LLC.
According to the Department, the application is made up of asphalt, water, an emulsifying agent (soap), mineral fillers, polymers and recycled materials. It contains no harmful chemicals, is compatible with traditional asphalt and can be spray- or squeegee-applied.
In addition to the Street Transportation Department and ASU, the City of Phoenix Office of Sustainability had also partnered on the project to see if the technology could help with the city’s continuing efforts to be environmentally sustainable while improving the quality of life for all who enjoy Phoenix.
Additionally, in July 2022, street crews and city officials in Los Angeles applied the first-ever cool pavement coating in the city as part of a $1 million project to combat heat and address heat related illness and death. On July 6, the coating was applied via paint roller to Bailey Street between Pennsylvania Avenue and First Street in Boyle Heights.
The light gray paint is a new high-tech coating to help lower ambient temperatures in asphalt-lined cities like Los Angeles.
In addition to lowering temperatures, the cooling element is expected to improve greening, pedestrian safety and public health. The federal funding will also go towards installing other cooling elements in the neighborhood.
At the time, the city had applied approximately 75 lane miles of cool pavement and planned to install another 175 lane miles by 2028, prioritizing the hottest residential areas.
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Now, city officials in Phoenix are reportedly hoping that the new cool pavement will help alleviate the city’s “heat island” effect, where heat absorbed by hard surfaces during the day is released at night, leading to higher temperatures even when the sun goes down.
According to a report from Fox Weather, July 15 marked the sixteenth consecutive day at 110 degrees F, or higher, this summer in Arizona. So far, the average high in July is reportedly 113 degrees F, with an overall average temperature of 100.6 degrees F.
According to one engineer, the Cool Pavement Program is like “sunscreen for the road”, applying a light-colored coating to existing pavement to reflect sunlight and absorb less heat. City officials state that the implementation of cool pavement will help keep the city livable as temperatures rise.
"I'm a native of Phoenix, so I want to make my community a better place to live," city engineering manager Ryan Stevens told Fox. "And so it's important to me to try to innovate and see how we can, again, make Phoenix cooler than it is even today and combat that heat so that we still have a Phoenix in 50 or 100 years from now."
According to the report, nighttime air temperatures at 6 feet above the ground are, on average, half a degree lower over cool pavement than on non-treated asphalt. Despite its benefits, residents have reportedly had mixed opinions of the cool pavement being rolled out in their neighborhoods.
"It's certainly a different color, so it has a certain aesthetic that some find pleasing, and others don't," Stevens said. "But every time we are out talking about cool pavement, I get comments of, 'When is my neighborhood next? How do I get my neighborhood on the list?' So a lot of people are interested."
So far, the city has reportedly coated around 100 miles of roadway with cool pavement and is aiming to reach 118 miles by the end of this year.
Additionally, according to KCRW News in Los Angeles, over the past four years the city of Los Angeles has lightened the pavement on hundreds of miles of streets in Canoga Park, Sun Valley and Pacoima, also lining many of those miles with trees.
The effort is reportedly part of the Cool LA project, which targets certain neighborhoods to paint streets a lighter color and plant more trees in those areas.
“I thought it was a silly idea until they did one half of the street before they did the other half,” said resident Ryan Solomon to KCRW. “And I was walking and it felt like a wave almost ... like if you're on the Metro or something, and you step outside, and you get that breeze of cold air.”
According to the report, as cities across the southwestern U.S. continue to face excessive heat warnings, the city of Los Angeles has plans to combat climate change by lowering local greenhouse gas emissions and looking at how to “make life tolerable” in the heat.
“Cool pavements work by having surfaces not absorb quite so much of that sun energy, and reflecting it back more quickly,” said UCLA Urban Planning and Geography Professor Kelly Turner, who has studied the program, to KCRW.
The city reportedly estimates that when the cool pavement is new, it reduces the surface temperature of roads by as much as 15 degrees F. However, this is not necessarily good news midday, because the reflection of heat reportedly makes the air above the street hotter.
“If you were thinking about cool pavement and you wanted to put it in, say, a playground at a school, that might not be the best choice because a playground is going to be getting its most use around 1 p.m. or noon,” Turner says. Later in the day, however, heat reduction is reportedly the most noticeable.
Additional efforts to plant trees in areas where the gray-wash has been applied have reportedly occurred, though the “drought ridden” landscape, combined with the time needed for the trees to grow, makes it less effective than the cool pavement.
“I don't think we have the carrying capacity for that in terms of our water supply,” says Jonathan Parfrey, founder of the LA-based nonprofit Climate Resolve. Parfrey reportedly supports the pavement-lightening approach.
“What are we going to do, given the fact that there's literally millions of miles of asphalt in the state of California? Why not put that to use?”
And after years of piloting the cool pavements, the city reportedly agrees.
“So many constituents are happy when we've applied cool paving in their neighborhoods.” LA’s Chief Sustainability Officer Ana Tabuena Ruddy states that the city will continue bringing lighter, more reflective paint to new neighborhood streets. "We are funded for over $4 million. And so we will definitely deliver that in the coming fiscal year.”