Heritage cores in post-colonial cities like Kolkata represent a rich blend of architectural, cultural, and socio-economic significance but face mounting pressures from urbanisation, particularly mobility demands and street transformations. This research examines their carrying capacity, exploring the interplay between mobility, spatial configurations, and heritage preservation, which is often overlooked. Street connectivity and integration are evaluated using space syntax analysis, which reveals movement patterns and accessibility. Axiality and choice values are layered with figure-ground maps and spatial data to identify critical mobility nodes. Pedestrian catchments were generated based on average walkability speed and accessibility to nearby bus stops. Key findings highlight significant gaps between urbanisation demands and transportation capacities, exacerbated by poorly connected areas and spatial shrinkages. Peak-hour and seasonal congestion intensify these challenges, emphasising the need for strategic interventions. Critical nodes and their performance for the next 50 years are identified for reducing congestion while safeguarding heritage, with scenario modelling demonstrating solutions like route diversions and mobility optimisation. The study underscores the potential of heritage-sensitive planning frameworks and digital spatial tools in addressing these challenges. Carrying capacity evaluation is vital for achieving sustainable urban management, offering a replicable framework to balance growth and cultural preservation in post-colonial cities globally.