Behavioural thermal regulation explains pedestrian path choices in hot urban environments

Abstract

Due to phenomena such as urban heat islands, outdoor thermal comfort of the cities’ residents emerges as a growing concern. A major challenge for mega-cities in changing climate is the design of urban spaces that ensure and promote pedestrian thermal comfort. Understanding pedestrian behavioural adaptation to urban thermal environments is critically important to attain this goal. Current research in pedestrian behaviour lacks controlled experimentation, which limits the quantitative modelling of such complex behaviour. Combining well-controlled experiments with human participants and computational methods inspired by behavioural ecology and decision theory, we examine the effect of sun exposure on route choice in a tropical city. We find that the distance walked in the shade is discounted by a factor of 0.86 compared to the distance walked in the sun, and that shadows cast by buildings have a stronger effect than trees. The discounting effect is mathematically formalised and thus allows quantification of the behaviour that can be used in understanding pedestrian behaviour in changing urban climates. The results highlight the importance of assessment of climate through human responses to it and point the way forward to explore scenarios to mitigate pedestrian heat stress.

Geographic Information System-Based Model of Outdoor Thermal Comfort: Case Study for Zurich

“…Another indicator for a conscious OTC-seeking route choice behavior is the lower T mrt for chosen paths compared with shortest paths, which becomes higher with increasing trip lengths (by 0.17°C for trips > 696 m, by 0.35°C for trips > 1 , 100 m, and by 0.68°C for trips > 1 , 500 m). This would be in line with the findings of Melnikov et al ( 32 ) and Lee ( 33 ) that pedestrians prefer to walk in the shade…”

“…1,500 m). This would be in line with the findings of Melnikov et al (32) and Lee (33) that pedestrians prefer to walk in the shade…”

“…If humans cannot cope with the stress caused by the microclimate and their physiological responses, they must adapt their behavior ( 32 ). Several studies confirm that pedestrians incorporate behavioral adjustments to maintain their HTS in balance.…”

“…Lee ( 33 ) found that it was not air temperature T air but global radiation GR from sunlight—which determines mean radiant temperature T mrt —that was the reason for pedestrians changing the side of the street in a study on four locations in New York City. A recent study from Singapore ( 32 ) examined the effect of shade on path choice. They found that pedestrians’ assumed walking time in the sun was 16% longer than on a shaded path.…”

“…Numerous studies show that trip length is the primary determinant for choosing a particular route (4,6,31). Broach and Dill (5) If humans cannot cope with the stress caused by the microclimate and their physiological responses, they must adapt their behavior (32). Several studies confirm that pedestrians incorporate behavioral adjustments to maintain their HTS in balance.…”