Unpacking the shade effect on street vitality: Land use, thermal thresholds, and urban-design determinants

Shade is a critical determinant of pedestrian thermal experience. Consequently, understanding when, where and how shade impacts pedestrian activity is key to designing heat-resilient streets that promote street vitality. This study aims to quantify shade’s impact on street vitality across land-use types and to identify the thermal thresholds and urban-form moderators under which shade enhances or suppresses pedestrian activity. Focusing on Jung-gu, Incheon, South Korea, we analyzed hourly mobile-phone–based walking counts and linked them to a modeled shadow ratio and observed air temperature and solar radiation across 50 × 50 m grids during August afternoons on precipitation-free days over five summers. Combining random-effects panel models with eXtreme Gradient Boosting for non-linear and interaction effects, we identified the thermal–radiation thresholds and spatial contexts under which shade supports or undermines street vitality. The results show that shade’s effects differ markedly by land use—largest and most consistent in commercial streets, but smaller or statistically weaker in residential, industrial, and green areas. The influence of shade is strongly conditional: it increases walking count under moderate heat but attenuates or turns negative as temperature and solar radiation intensify. Urban form further modifies these patterns, with shade most effective in very open or very compact settings, while greater sky openness consistently strengthens performance. Together, these findings indicate that shade affects street vitality through interactions among temperature, radiation, and morphology, thereby offering context-specific guidance for climate-sensitive street design.