With rapid urbanization, interest in outdoor thermal comfort has increased, particularly in semi-open transitional spaces such as areas beneath overhead shelters that are frequently used during commuting. This chapter presents an experimental study conducted at Guangzhou University to investigate transient thermal comfort during walking and resting activities in such spaces. Thirty participants performed 20 min walking trials at different speeds, followed by a 10 min rest, while both subjective thermal responses and objective microclimatic data were collected. The analysis focused on the influence of metabolic rate variation and the relationship between mean thermal sensation votes (MTSV) and widely used indices, including PET and UTCI. Results show that the time required for metabolic rate stabilization is significantly longer in semi-open spaces compared with indoor settings, and that turbulence intensity has a pronounced effect on convective heat transfer. Neglecting this factor leads to an overestimation of body heat storage by about 20%. Based on these findings, a refined predictive model was developed that effectively captures thermal comfort across both dynamic and stationary conditions, offering practical implications for designing safe and comfortable commuting environments.