Tucson Cool Pavement Pilot 2021

Project Description

In December 2021, the City of Tucson laid down its first cool pavement as a pilot. The product used - PlusTi from Pavement Technologies - includes titanium dioxide to reflect UV rays back into the atmosphere. It is basically a mineral sunscreen for the road.

The City chose this product because it is visually indistinguishable from normal pavements. The product goes on as a yellow-beige with the titanium dioxide suspended within an asphalt rejuvenator. Within an hour or two, it has soaked in, doing its work for as long as the pavement exists. No need to restripe. Also, given the sun and heat exposure in the region, we can take whatever rejuvenation product we can get on our roads!

In anticipation of this pilot, our team sought funding from the National Institute of Transportation and Communities to (a) do a pre/post evaluation of heat and (b) consider the technology in the larger context of multi-modal travel.

The evaluation of this cool pavement pilot is exploring both a pre/post and case/control design to document changes in surface temperatures, ambient temperatures, and thermal comfort. We anticipate lessons from this evaluation will be highly applicable elsewhere as cities go all-in on cool pavements as part of the environmental-justice oriented $500 million Healthy Streets Program passed in Congress in 2021.

How Our Team Measures Personal Heat Exposure

Choosing Site and Times

Cool pavements are well tested in laboratory settings, but less studied in real-world settings. This is partly due to the newness of the technologies. But it is also related to the difficulty of controlling for street types, green space along the street, and weather.

Addressing variation in weather can be somewhat controlled through careful consideration of data collection timelines. We went out on 3 days in late October to gather "pre" data. October was chosen due to funding cycles and the need to not have high humidity levels that occur only in July-September. We will go out in early March to match approximate day length and high temp patterns. Within models, we will control for background ambient temperatures. We generally collect data during the heat of the day (10am-3pm) for maximum surface temps and at dawn to understand the potential for overnight cool-off.

The City of Tucson, in coordination with the vendor, chose the pilot site - a 1.5-mile length of Country Club south of Broadway and north of Aviation Hwy. The research team noted three distinct street typologies within the chosen site and is playing with a methodology to "match" the sites with nearby controls that account for the width of the street, green infrastructure, and presence/absence of pedestrian facilities (sidewalks).

Surface Temperatures

IR (Heat Gun) measurements were taken on the hour (starting at 10:00 AM) with a repeat measurement approach. All measurements taken with the heat gun were logged on REDCap to secure data measured. Measurements were collected at each site on the nearest road, sidewalk, and gravel or grass surface.

In addition to basic information such as collector's name, segment, and location, we logged:

1) Surface composition

2) Whether the surface was in the sun, shade, or partial shade

3) Surface Temperature readings (repeated at each point 5 times) from the heat gun.

Ambient Temperatures

For this study, we used Kestrel 5400 devices which are able to measure Wet Bulb Globe Temperature (WBGT), ambient air temperature, solar insolation, and wind speed. Ambient air temperature is measured at the Kestrel 5400’s thermistor. It provides a general level of heat and is analogous to the weather station readings shared in general society.

In total, we used 8 different Kestrel 5400 devices. we set the Kestrel devices to record data every 10 seconds from 10 A.M. to 3 P.M. We placed Kestrels in 2 groups of 3: centerline and the pedestrian right of ways on each side. The remaining Kestrels were used to explore the possibility of using a nearby analogous street as a control.

Thermal Comfort for Personal Heat Exposure

Measuring ambient air temperatures, even at a microscale level, does not give information about how a person will feel about the heat in the context of all weather conditions such as moisture, winds, or evaporative cooling. In Arizona, it does not capture the vast swing in comfort between sun exposure and shade. It also does not capture the amount of heat radiating up from surfaces such as the road or nearby concrete block walls. This is why using a thermal comfort index is critical when discussing pedestrian, cyclist, and transit rider comfort along our roadways.

Wet Bulb Globe Temperature (WBGT) is one of the major thermal comfort or personal heat exposure measurements used throughout the world. It expands the concept of ambient air temperature to incorporate solar heat that beats down on the Kestrel 5400’s black, copper globe and humidity measured at the Wet Bulb. Wind, ambient air temperature, humidity, and solar radiant heat are all considered in order to approximate thermal comfort. WBGT is the standard for occupational uses such as for the US military and athletic outdoor sports.

The Kestrel 5400 provided us with WBGT measurements every 10 seconds from 10 A.M to 4 P.M and were placed as mentioned in the previous section.

Explore Media Coverage of Tucson's Cool Pavements

KVOA Tucson Article

UArizona "cool pavement" program aims to beat Tucson's extreme heat

Dec 15, 2021

City of Tucson Press Release

Cool Pavement Country Club Road

December 10, 2021

CAPLA Article on NITC Grant

CAPLA Urban Planning Professors Awarded $150,000 in NITC Research Grants

August 27, 2021

NITC Cool Corridor

Assessing Cool Corridor Heat Resilience Strategies for Human-Scale Transportation


Learn more about the Healthy Streets Program in the 2021 Federal Infrastructure Bill

U.S. infrastructure bill aims to cool heat inequity in cities

The $1.2-trillion, 2,702-page infrastructure bill passed on November 6, 2021. As part of the bills efforts to mitigate the Urban Heat Island Effect, the bill contains a "Healthy Streets Program" which will allow state and local governments to apply for grants of up to $15 million for applications of "cool" pavements on roadways, to boost tree canopies in disadvantaged areas, and more. Governments who receive the funds can also use them to conduct "equity assessments" such as mapping tree canopy gaps, flood-prone locations, heat island hot-spots, and areas where these risks overlap.

Applicants to the program must specify how the projects will benefit disadvantaged and low-income communities (locations where at least 30% of residents live below the poverty line).

Infrastructure Bill Boosts Equity Focus for Urban Tree Plantings

The Healthy Streets Program of the infrastructure bill authorizes 100 million a year for five years under a federal grant program. Aside from providing support to cities in using "porous" and "cool" pavements, which absorb stormwater and reduce urban hot spots, the program will also encourage purchasing and planting of trees and development of a tree canopy plan.

The Biden administration has vowed to provide more resources to low-income and minority communities who have been marginalized by large-scale transportation projects in the past. Tree planting and different pavement programs have been seen as a key provision to meeting these goals.

Other Notable Cool Pavement Projects

Cool L.A. Neighborhoods

On June 2019, The City of L.A. completed a pilot program to apply "cool pavement" to three neighborhoods in L.A.

With researchers from UCLA, USC, and ASU, L.A. has been evaluating the heat comfort benefit of these projects. Read more here:

Los Angeles is painting some of its streets white and the reasons why are pretty cool (CBS News)

Cool LA Neighborhoods Website

Global Cool Cities Alliance

Launched in December 2020, the Cool Roadways Partnership seeks to improve resilience against extreme heat by accelerating the development of pavement projects that reduce surface and air temperatures. The map above shows current participants in the Cool Roadways partnership across the U.S. Read more about the Cool Roadways Partnership in the following page:

Cool Roadways Partnership Website


ASU Cool Pavement Report

On July 2019, a month after L.A. placed cool pavements in three of its neighborhoods, researchers at ASU and UCLA collected data in two of those neighborhoods in L.A.

Using a device called MaRTy, a mobile platform that measures air, surface, and mean radiant temperature, these researchers discovered that while cool pavements reduce surface temperatures, they may negatively influence the heat a pedestrian feels. Read more here:

'Cool pavement' experiments help urban planners find ways to ease rising temperatures (AZ Central)

Solar reflective pavements—A policy panacea to heat mitigation? (ASU Research Paper)

Photo Gallery

View us and our Kestrels in the field collecting data prior to the application of the cool pavement application in the following photo carousel.