Road pavement is a known contributor to the urban heat island effect. Several vendors are providing engineered pavements coatings – known as “cool pavement” - to reflect light and therefore heat to reduce the thermal load of roads. The City of Tucson is planning a pilot application of a cool pavement in Fall 2021 as a part of its Parks and Connections Bond work; our team has been working with the city and vendor(s) to set up an evaluation framework of the cool pavement.
Few of these cool pavements have been evaluated outside lab conditions, particularly in the desert southwest. Lab testing tends to rely heavily on surface temperature measurements with the assumption that lower surface temperatures result in the pavement being less of a heat sink and thus lowers ambient temperatures in real-world practice. Further, while heat is detrimental to the pedestrian and cyclist experience and health, almost no research exists documenting the experience of the cool pavement on active travelers including their perception of heat.
We propose a pre/post, case/control quasi-experimental design to evaluate the impacts of the cool pavement on the following heat metrics:
• Surface temperatures of the pavement
• Ambient temperatures of the area
• Thermal comfort as measured by wet bulb globe temperature (WBGT) - Governmental occupational guidance for exertion for heat is based on studies in industrial settings using wet-bulb globe temperature (WBGT), a heat index that incorporates ambient air temperature, humidity, airflow, and radiant solar heat. Known as “thermal comfort”, this index better mirrors the human – and thus pedestrian and cyclist - experience.
We anticipate four 12-hour days in the field. Each day will include seven Kestrel 5400 stations for ambient and WBGT temperatures at least every minute and surface temperatures every hour. Data will be managed and analyzed in R; outputs will include basic summary statistics, graphics, and regression analysis.
Our team has steadily increased capacity for such research over the past 2 years. In summer of 2019, Iroz-Elardo and Keith piloted a methodology to investigate how shade structures and surface materials in school gardens and play structures influenced thermal comfort as measured with a WBGT instrument and thermal heat guns. In late-spring 2020, Keith and Iroz-Elardo applied this knowledge to evaluate heat risk at COVID-19 vaccine point of distribution (POD) drive-in centers in Tucson. One of the more interesting preliminary findings from the vaccine POD evaluation was the extent to which idling vehicles appear to raise the WBGT in outdoor settings due to both mechanical and radiant heat.