"Cosmopolitan Canopy" in Hong Kong's hidden city: Urban design and social life in underground transit hub.

• Central Station underground exemplify efficient infrastructure and effective urban design. • The high intensity of underground public spaces promotes social integration. • The efficiency of travelators decreases when the density exceeds one person per square foot. • The narrow widths of travelators limit casual conversations by restricting eye-gaze and turn-taking. • Underground public spaces extend the conventional public realm contributing to the vibrancy of the overall public sphere. This paper investigates how Hong Kongers navigate and utilize the corridors, tunnels, and public spaces of the underground transit hubs at Central Station and Hong Kong Station, accommodating over 250,000 passengers daily. Employing participant observation protocols from urban design research, we documented the locations of social activities and surveyed people's behavior in these underground environments. Despite their grand and efficient engineering, the efficiency of travelators decreases when density exceeds one person per square foot. The narrow widths limit casual conversations. Our findings reveal that people navigate and behave in underground public spaces similarly to above-ground spaces. Additionally, cheaper rents in mezzanine shops and restaurants have enabled these businesses to thrive, benefiting from substantial foot traffic within the transit system. Overall, underground public spaces extend the conventional public realm, catering to diverse social groups and contributing to the vibrancy and vitality of the overall public sphere. [ABSTRACT FROM AUTHOR]