A generalized two-step floating building catchment area model for measuring EMS accessibility with in-building patient access

Rapid access to Emergency Medical Services (EMS) is critical for improving patient survival. Existing studies primarily assess EMS accessibility based on road travel, overlooking the in-building time required to reach patients, which may introduce bias in high-density urban environments. This study aims to improve the measurement of EMS accessibility by explicitly incorporating in-building patient access. We developed a generalized two-step floating building catchment area (G-2SFBCA) model that integrates both the Departure Road Trip (DRT) and the Patient Access Trip (PAT), while accounting for spatial variations in building height and occupancy density. Wuhan, China, was used as a case study. Building-level data, EMS station locations, and road network data were combined to estimate total EMS travel time. Accessibility was evaluated under different distance-decay functions and compared with results from the conventional G-2SFCA model. PAT travel time exhibited a distinct “low–high–low” spatial pattern from the city center to suburban areas, closely associated with variations in building height and density. Incorporating PAT reduced the population covered within a 5-minute EMS response time by 12.9% and increased the population outside the 12-minute threshold by 3.2%. Compared with the conventional model, the proposed approach revealed lower accessibility in transitional high-rise areas and highlighted the overestimation of EMS accessibility when in-building travel time is ignored. The proposed G-2SFBCA model provides a more realistic and policy-relevant assessment of EMS accessibility, revealing that conventional approaches may substantially overestimate service coverage in high-density urban environments.