Equitable access to tertiary hospitals is a critical concern in urban planning, yet conventional assessments often rely on static proximity assumptions and fail to capture the dynamic interplay between traffic conditions and residents' hospital‑selection behaviour. This study proposes an improved two‑step floating catchment area method that integrates a power‑law probabilistic choice function to simulate residents' preferences beyond the nearest‑facility rule, a continuous Gaussian decay to replace binary thresholds, and year‑round real‑time traffic data from routing APIs to measure dynamic accessibility across weekday/weekend, peak/off‑peak periods, and multiple time thresholds (5, 10, and 30 minutes). Applied to Chengdu—a megacity with 59 Grade‑A tertiary hospitals—the analysis reveals a three‑tier spatial gradient from central urban areas to inner and outer suburbs. Notably, inner suburbs fall within the 30‑minute catchment but exhibit severe functional insufficiency, with up to 90% of critical care relying on central‑city referrals. Global spatial autocorrelation is significantly positive, intensifying with larger thresholds (Moran’s I: 1.12–1.21 at 30 minutes), confirming that the concentration of 80% of top‑tier hospitals within the ring road is the dominant driver of inequity. Residents' choice behaviour deviates markedly from the nearest‑principle, and weekend leisure traffic further disrupts access in tourist hotspots, reflecting the city's “leisure‑oriented transition”. These findings underscore the necessity of decentralising medical resources through regional sub‑centres in accessibility blind zones and implementing adaptive traffic management, such as dynamic bus‑lane policies, to enhance off‑peak response efficiency. The improved method demonstrates high robustness across parameter sensitivity, data perturbation, and cross‑validation. This study provides quantitative evidence for urban planners to reconcile resource agglomeration with transport dynamics, advancing spatial equity in medical service delivery.

Urban Healthcare Accessibility, Tertiary Hospitals, Two‑step Floating Catchment Area, Spatial Equity, Traffic Dynamics, Chengdu, Urban Planning, Spatiotemporal Heterogeneity