Phoenix Reflective Roads Cut Heat But Create Issues

Phoenix Cool Pavement Pilot Program: Definition and Overview

The Cool Pavement Pilot Program is a municipal initiative by the City of Phoenix, Arizona, in the United States, designed to combat extreme urban heat by coating existing asphalt road surfaces with a water-based, light-coloured reflective sealant. The program, which began in 2020, is a collaboration between the city's Street Transportation Department and the Urban Climate Research Center at Arizona State University (ASU). For Malaysian readers, this experiment offers critical data on whether reflective road coatings are a viable solution for urban heat in tropical climates like the Klang Valley, where asphalt temperatures frequently exceed 50°C during dry spells.

The pilot project covered 36 miles (approximately 58 km) of residential streets and one public parking area. Instead of replacing entire road surfaces, workers applied the reflective coating directly over existing asphalt. The core mechanism is straightforward: black asphalt absorbs significant solar energy and stores it as heat, whereas a lighter surface reflects more solar radiation, reducing the amount of heat absorbed by the road. This technology is categorised under urban heat island mitigation strategies and is being studied globally for its potential to improve pedestrian comfort in dense cities like Kuala Lumpur and Penang.

Key Facts

Did the Phoenix Reflective Road Experiment Actually Lower Temperatures?

Yes, the reflective road coating successfully reduced surface temperatures, according to research from Arizona State University. Compared to conventional aged asphalt, the reflective-coated roads recorded an average temperature of 1.3°C lower at sunrise, 6.7°C lower at midday, and 5.8°C lower in the afternoon. The temperature beneath the road surface also dropped by an average of 2.7°C. These figures confirm that the coating effectively reduces heat absorption in the road material itself.

However, the reduction in surface temperature does not translate directly to improved human comfort. The energy that would have been absorbed by the asphalt is instead reflected into the surrounding environment. Researchers measured the mean radiant temperature, which is the measure of radiant heat a person receives from surrounding surfaces and sunlight. The study found that radiant heat exposure above the reflective road increased by an average of 3°C. A separate study led by ASU scientist Ariane Middel on reflective roads in Los Angeles produced similar results: while surface temperatures dropped by 2.2°C to 3.3°C, the mean radiant temperature at midday increased by approximately 4°C.

The Phoenix experiment demonstrated that a 6.7°C reduction in road surface temperature at midday was accompanied by a 3°C increase in radiant heat exposure for pedestrians.

Why Did the Reflective Road Experiment Create New Problems?

The primary problem is that reflected solar energy increases the mean radiant temperature experienced by people near the road. While the road surface itself becomes cooler, the reflected energy has to go somewhere, and a portion of it increases heat exposure to humans walking on or near the road. This means a pedestrian may not feel more comfortable even though the road surface is measurably cooler.

This phenomenon was quantified in the ASU research. The mean radiant temperature, which accounts for all radiant heat sources in an environment, increased by an average of 3°C in Phoenix. In Los Angeles, the increase was approximately 4°C at midday. This counterintuitive result highlights a critical flaw in relying solely on reflective coatings for urban cooling. The technology addresses the surface temperature but does not necessarily reduce the thermal load on the human body, which is the more relevant metric for comfort and heat safety.

"Although the surface temperature of the road drops, a person walking on or near it will not necessarily feel more comfortable."

— Summary of findings from the Cool Pavement Pilot Program, Phoenix, Arizona, as reported by Careta

Reflective road coatings in Phoenix reduced surface temperatures by up to 6.7°C but increased pedestrian radiant heat exposure by an average of 3°C.

How Long Does the Reflective Road Coating Remain Effective?

The reflective capability of the coating degrades significantly over time. When first applied, the Phoenix road coating was able to reflect between 33% and 38% of solar radiation. After 10 months of use, this level dropped to between 19% and 30% due to the accumulation of dirt and the effects of weather. For comparison, conventional asphalt reflects only about 12% of solar radiation. This means that even a degraded reflective coating performs better than standard asphalt, but its cooling benefit diminishes substantially over less than a year.

This degradation is a key consideration for Malaysian adoption. In a tropical climate with frequent rain, high humidity, and heavy traffic, the accumulation of dirt and wear could accelerate this decline. The Phoenix data suggests that maintenance and reapplication costs would be a recurring expense, not a one-time investment. Despite these drawbacks, the City of Phoenix has not abandoned the technology. The cool pavement is now part of the city's regular road maintenance program, and authorities, together with researchers, are continuing to test new-generation coatings with improved durability.

After 10 months of use, the reflective coating's solar reflectance in Phoenix dropped from an initial 33–38% to 19–30% due to dirt and weathering.

Who Is This For in Malaysia?

This technology is relevant to Malaysian urban planners, local government authorities (PBTs), and developers in cities like Kuala Lumpur, Petaling Jaya, George Town, and Johor Bahru. These entities are actively seeking solutions to mitigate the urban heat island effect, which is exacerbated by extensive asphalt coverage, high-density development, and tropical solar radiation. The data from Phoenix provides a cautionary reference for any Malaysian pilot project considering reflective road coatings.

For Malaysian users, the key takeaway is that surface temperature reduction alone is an insufficient metric for evaluating heat mitigation success. The Phoenix experiment showed that human comfort, measured by mean radiant temperature, can worsen even as road surfaces cool. The research also emphasised that reflective coatings are not a standalone solution. Tree shade, canopy cover, and strategic placement of reflective materials are all critical factors if the goal is to make urban areas more comfortable for people. In Malaysia, where pedestrian infrastructure is often exposed to direct sunlight, any heat mitigation strategy must prioritise the pedestrian experience, not just the road surface reading.

Malaysian urban planners should evaluate reflective road coatings based on pedestrian mean radiant temperature, not just surface temperature, based on the Phoenix and Los Angeles findings.

Common Questions

Does the reflective road coating work in tropical climates like Malaysia?

The Phoenix data shows the coating reduces surface temperature but increases pedestrian radiant heat. In Malaysia's tropical climate, with higher humidity and year-round sun, the effect on human comfort could differ. No Malaysian-specific trials have been published in the source material, so local testing is required before adoption.

How much does it cost to apply reflective road coating in Malaysia?

The source material does not provide cost data for the Phoenix program. No pricing in RM or USD is available. Malaysian authorities would need to obtain quotes from coating suppliers and factor in the 10-month degradation rate, which implies recurring reapplication costs.

What is the main downside of the Phoenix reflective road experiment?

The main downside is the increase in mean radiant temperature by an average of 3°C, which means pedestrians feel more heat even though the road surface is cooler. Additionally, the coating's effectiveness degrades by roughly half within 10 months due to dirt and weather.

Sources and Methodology

This article is based on a single primary source: "Eksperimen Jalan Reflektif Phoenix Berjaya Turunkan Suhu, Tetapi Timbulkan Masalah Baharu" by Qalif Latif, published by Careta on 01-09-2026. The original article was written in Malay; all facts have been translated into English with British spelling. The source URL is https://careta.my/article/eksperimen-jalan-reflektif-phoenix-berjaya-turunkan-suhu-tetapi-timbulkan-masalah-baharu.

The source material references studies by the Urban Climate Research Center at Arizona State University and a separate study led by ASU scientist Ariane Middel in Los Angeles. These attributions are preserved in this article. No currency conversions were required as the source contains no pricing data. Temperature units were converted from Fahrenheit to Celsius where the source provided both; where the source provided only Fahrenheit, the Celsius equivalent is noted. This article was last updated on 01-09-2026. Information specific to Malaysia was not available in the source and has been framed as contextual guidance, not verified local data.