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Cool Pavement Pilot Project - Tramonto Community

Cool Pavement Program

The City of Phoenix Street Transportation Department and Office of Sustainability announced during a virtual presentation and panel discussion on September 14, 2021 the results of the first year of its Cool Pavement Pilot Program. The program and analysis of the cool pavement process is being conducted in partnership with Arizona State University (ASU).

Year one of the study done by scientists at ASU's Global Institute of Sustainability and Innovation, Healthy Urban Environments, and the Urban Climate Research Center revealed that reflective pavement surface temperatures are considerably lower than traditional roadway pavement. 

​Cool pavement coating reflects a higher portion of the sunlight that hits it, hence absorbing less heat. Because of this higher reflection, the coating has the potential to offset rising nighttime temperatures in the region.​

Findings from year one of the study include:

  • Cool pavement revealed lower surface temperatures at all times of the day versus traditional asphalt.
  • Cool pavement had an average surface temperature 10.5 to 12 degrees Fahrenheit lower than traditional asphalt at noon and during the afternoon hours. Surface temperatures at sunrise averaged 2.4 degrees Fahrenheit lower.
  • Sub-surface temperatures averaged 4.8 degrees Fahrenheit lower in areas treated with cool pavement.
  • Nighttime air temperature at six feet of height was on average 0.5 degrees Fahrenheit lower over cool pavement than on the non-treated surfaces.
  • The human experience of heat exposure at noon and the afternoon hours was 5.5 degrees Fahrenheit higher due to surface reflectivity, but similar to walking on a typical concrete sidewalk.
  • Surface solar reflectivity declined over 10 months from a range of 33 to 38 percent to a range of 19 to 30 percent across all eight neighborhoods. Untreated asphalt has a reflectivity of only 12 percent.

Read the Executive Summary of ASU's Scientific Study (published September 2021)
​​

 View Scientific Testing Results - Joint City of Phoenix/ASU Presentation

​​Learn More About the Program

​In 2020, the city selected portions of eight neighborhoods, one in each City Council district and part of the parking lot in Esteban Park, to receive cool​ pavement treatment. The asphalt coating was applied to areas already in need of pavement preservation. The city then partnered with ASU researchers to conduct scientific tests of the cool paved areas, studying how it performed and how it might be used to mitigate the urban heat island effect.

Scientific data collection during year one of the study included thermal imaging through helicopter flyovers, temperature sensors embedded in the pavement surface, and other advanced instruments to conduct testing across various heat metrics. ASU researchers also developed MaRTy (derived from 'Mean Radiant Temperature'), a specially designed mobile weather station that evaluates the human experience of heat by measuring 3D mean radiant temperature, air temperature, relative humidity, and wind speed and direction. Additionally, a vehicle equipped with air and surface temperature sensors traveled over the treated areas to gather data during four times of the day.​

What is cool pavement?
It is a water-based asphalt treatment that is applied on top of the existing asphalt pavement. It's made with asphalt, water, an emulsifying agent (soap), mineral fillers, polymers and recycled materials. It contains no harmful chemicals and is compatible with traditional asphalt.

Why would Phoenix apply cool pavement?
Asphalt collects and retains heat during the day and releases it at night. Phoenix is among several cities that are experiencing the urban heat island effect due to the retention of heat within the built environment. U.S. Environmental Protection Agency data shows the difference in nighttime temperatures in heat island areas can be as much as 22 degrees warmer than temperatures measured outside the heat island. Higher nighttime temperatures lead to more energy consumption, more greenhouse gas emissions, air pollution and other harmful effects.

Cool pavement reflects back the sunlight that hits it. Because the surface reflects rather than retains heat, cool pavement has the potential to offset rising nighttime temperatures in Phoenix. The use of cool pavement technology may help reduce the heat island effect and reduce temperatures in the city. It is also useful to cool neighborhood areas that don’t have much shade from the sun.

Phoenix participated in a workshop hosted by the federal government and the City of Los Angeles. Los Angeles has been using cool pavement on neighborhood streets and has reported positive results in reducing roadway surface temperatures.

​Why is this a pilot project?Regular asphalt shown with temperature reading of 121 degrees, other photos showing cool pavement and temperatures from 111 to 106 degrees
The Street Transportation Department is always looking for ways to improve what it does and improve the livability of the city. Phoenix wants to test the cool pavement technology and material to see whether it is effective at reducing temperatures in Phoenix's desert climate. City staff has engaged university researchers to take measurements and collect data over several years. They will evaluate the results and help the community understand if the cool pavement product helps mitigate the heat island effect and if those effects are sustainable over time. ​

The department also wants to learn how the product holds up. The Phoenix climate is unlike other major cities. We want to make sure it will last through our 300 days of sunshine, monsoon storms, high temperatures and daily traffic.

Where are you testing cool pavement?
The Street Transportation Department identified local streets in each City Council district for cool pavement treatment. Since different parts of the city experience different rain, monsoon conditions, and degree of wear on the pavement, it should be a good way to find out how well it is working and how durable it is.

The streets selected for this pilot project have asphalt that is in good condition and where a preservative surface treatment would be warranted. Preservative treatments extend the life of the road by sealing any surface cracks to prevent moisture intrusion and improve the overall road condition and appearance.

How can my neighborhood get cool pavement?
Before adopting this technology on a more widespread basis, we want to examine the results from the pilot program. Cost will also be a consideration, as the city works to use taxpayer funds wisely. While the cool pavement material is more costly than the seal coating materials we usually use, results from other cities suggest the material is effective and longer lasting than traditional asphalt seal coats. If that’s true in Phoenix, and the material provides the environmental benefits we believe it will, you can expect to see wider use of cool pavement when neighborhood streets are due for pavement maintenance.

Pavement condition is one of the key criteria for future installations. We will also try to solve community challenges such as providing heat relief to areas with very little shade. Future installations will be studied to ensure the cool pavement is placed equitably and in areas where the immediate benefit is most needed – such as areas with little or no shade or areas where people move on foot or bicycle out of necessity.

Can I buy the cool pavement material and treat my driveway with it?
As most Phoenix driveways are concrete, it's unlikely the product would work for that application. The product is formulated to bond to underlying asphalt, and it’s also applied with specialized equipment over a larger area. There may be other types of coatings available – such as those used on concrete around pools – but they are probably not meant to handle vehicle movement.

Does cool pavement look different than traditional asphalt?Cool Pavement Application at Esteban Park
Yes, the cool pavement coating is a lighter grayish concrete color. This photo of Esteban Park gives a sense of the color. The material dries to a matte finish.

Is cool pavement safe to use?
It is safe for all types of vehicles, pets, people and all the typical activities that would take place on a road. Despite being lighter in color, cool pavement does not result in glare. It also meets or exceeds skid safety requirements.

Is this a new product?
Colorized seal coats and asphalts have been around for a while. Cool pavement uses existing material and technology in a new way.

How is cool pavement applied?
It can be sprayed or applied with a squeegee, just like the other surface treatments we apply to city streets.

City of Phoenix Crew Applying Cool PavementThis photo shows crew members using squeegees to smooth the edges after the cart has applied the material. 

Who are the partners in this project?
The City of Phoenix Office of Sustainability, the Street Transportation Department and Arizona State University are partnering to learn if this project can help with the city’s continuing efforts to be environmentally sustainable while improving the quality of life for all who live in the region.

Is there a difference in skid resistance between regular asphalt and cool pavement?
A friction test was conducted with the Arizona Department of Transportation (ADOT). The friction test was conducted at 40 MPH. While there are no established standards for skid resistance on 25 MPH neighborhood streets, the Street Transportation Department saw value in conducting a friction test as a baseline for future evaluations. The test measured friction in wet conditions. Staff found no safety concerns for people walking, driving or bicycling on streets coated with cool pavement.

Where can I see cool pavement?
The Street Transportation Department applied cool pavement to a portion of the parking lot and driveways at Esteban Park. See below for other pilot test locations citywide.

Cool Pavement Pilot Program Locations:                                                              

Mayor - QS: 11-30 - Van Buren St. / Roosevelt St. from 12th - 16th St.

District 1 - QS: 33-18 - Thunderbird Rd. / Acoma Dr. from 47th - 43rd Ave.

​District 2 - QS: 59-23 - Carefree Hwy. / Languid Ln. from OPEN SPACE / 27th Ln.

District 3 - QS: 29-37 - Shea Blvd. / Cholla St. from 40th - 44th St.

District 4 - QS: 11-22 - Van Buren St. / Roosevelt St. from 31st - 27th Ave.                         

District 5 - QS: 18-16 - Campbell Ave. / Camelback Rd. from 55th - 51st Ave.

District 6 - QS: 26-28 - Las Palmaritas Dr. / Dunlap Ave. from Central Ave. - 7th St.

District 7 - QS: 2-19 - Vineyard Rd. / Southern Ave. from 43rd - 39th Ave.

District 8 - Esteban Park: 3345 E. Roeser Rd. - Parking Lot

Contact Information:

Project Hotline: 623-825-3444​
pavement@phoenix.gov

 Cool Pavement Application at Esteban Park

 Public Meeting - June 2020


Associated Press Cool Pavement Article (this link will take you to the news site)

Arizona Republic Article from 5-15-2020 (this link will take you to the news site)

Cool Pavement Street Cut Guidance