Exploring Urban Heat as a Pedestrian: A MaRTy Cart Study of Tucson, Arizona in June 2025

Abstract

In this study, we used a mobile biometeorological cart, the MaRTy Cart, to collect measures of heat, such as mean radiant temperature (MRT), a proxy for how humans experience heat that takes into account radiant heat coming from all directions, including the sun. We first identified five routes, called transects in this report, with stops strategically located for data collection. These stop locations provide different types of shaded environments that pedestrians experience. For each transect, we collected data during three time periods (8-9 AM, 12-1 PM, and 4-5 PM) on a day in June 2025. We aimed to collect data at locations frequented by pedestrians to understand the implication of different types of shade on heat stress. We were particularly interested in shade provided by(a) trees, (b) bus stop shelters, and (c) buildings.

Of the three types of shade studied here, we compared the MRT for stops with shaded environments with a full-sun base case on the same transect and time period. The difference in temperature between the shaded area and full sun comparison provides an estimated impact of shade for each type of environment. In our study, we found MRT under trees to be 15-21°C cooler on average compared to sun-exposed locations, depending on the time of day. Bus stop shelters provided, on average, 15°C (MRT) cooling compared to their full-sun base case, and building shade was 23°C cooler on average.

In this report, we describe the equipment and study design, present results for our comparisons of shade (trees, bus stop shelters, and buildings), and provide a discussion of findings and potential future work. We provide two appendices that document our data collection protocols (Appendix A) and observations for each stop across all five transects and three time periods (Appendix B).