By Hailey Pederson, EIT
With temperatures rising around the globe, many public agencies are looking for ways to lower the dreaded “heat island effect” that often plagues major cities. Heat Islands are defined as areas in which there is a significant temperature differentiation between the neighboring urban and rural areas. That difference can be as high as 22 degrees F in the evening after a long hot day. According to the Environmental Protection Agency (EPA), heat islands can negatively affect those living in the urban community by increasing energy demands, air conditioning costs, air pollution and greenhouse gas emissions, mortality rates due to heat-related illnesses, and even water quality.
One culprit of the heat island effect is dark pavement. It absorbs more sunlight and becomes drastically hotter during summer days as anyone walking through a large surface parking lot will tell you. A recent American Society of Civil Engineers’ (ASCE) Civil Engineering magazine article detailed a pilot project of the City of Los Angeles to combat heat islands, dubbed “cool pavement.” Being implemented in all 15 city districts, the “cool pavement” project is intended to help reduce the urban/rural temperature differential in the area, ideally by 1.7 degrees Fahrenheit by 2025 and 3 degrees Fahrenheit by 2035.
The plan involves coating the city’s asphalt roads with CoolSeal©, “a high-performance, water-based, asphalt emulsion sealcoat” manufactured by Guard Top LLC. CoolSeal© works to mitigate the heat island effect by lowering the surface temperature of the pavement through a matte grey color coating of the existing asphalt layer. The lighter color increases the reflectivity of the sun’s energy. CoolSeal© is applied the asphalt in the same manner as traditional sealcoats and can be applied to coat a variety of surfaces including playgrounds, parking lots, bike paths, and driveways.
In preliminary tests, CoolSeal© has performed extraordinarily well. At one location, the treated surface registered at only 70 degrees Fahrenheit whereas the surface temperature at a nearby intersection (with darker pavement) registered at 93 degrees Fahrenheit.
Feedback from those in the community has also been quite positive. Chi Ming Gong, P.E., who is a street services superintendent in the Methods and Standards Division of Los Angeles’s Bureau of Street Services, comments that the pavement surface “stays cool enough that they don’t wince when they decide to walk barefoot across the street.” The City’s General Services Department has also deemed that CoolSeal is “suitable for use in public,” and “has an adequate amount of traction and visibility as well as durability.” As an added highlight, all CoolSeal products also meet LEED and EPA requirements of 33% reflectivity and are eligible for LEED points.
Though CoolSeal© may seem to be an easy fix for cities trying to combat the heat island effect, there are also some major downsides to the product. Regarding cost, CoolSeal is certainly not cheap at an estimated $40,000 per mile to apply, but it also only needs to be re-applied every five to seven years on average, meaning that the life of the CoolSeal coat is about twice as long as that of a traditional sealcoat. Roadways with obvious surface defects or utilities directly beneath the surface also need to be avoided, as there is no point in putting down this material just to turn around and tear it back up when the road needs repair or the utilities must undergo maintenance or repair.
Los Angeles’s pilot program is expected to run through fall of 2018 in order to gather information on how the sealant performs “through all the seasons, the hot weather, the rainy weather,” and also under a variety of traffic conditions Gong explains. The publicity surrounding program has already led to inquiries into CoolSeal from countries such as Australia, Israel, China, and Saudi Arabia, so, depending on results from Los Angeles, grey streets may start popping up worldwide.
The heat island effect and climate change are not things we directly study (although, arguably, if our studies help improve traffic flow with less delay, air emissions would decrease). However, it’s encouraging to see new products and technologies that will help us mitigate these issues. Hopefully the price will decrease, and our client cities will soon be able to benefit from items like this as well.
Reid, Robert. “Los Angeles Project Seeks Cool Solution to Hot Asphalt.” Civil Engineering, ASCE, January 2018
“Cool Pavement Sealant |CoolSeal | GuardTop | Asphalt Coating.” GuardTop® Asphalt Sealcoating Products
Holley, Peter. “Why L.A. Is Coating Its Streets with Material That Hides Planes from Spy Satellites.” The Washington Post, WP Company, 18 Aug. 2017