Pathfinder-Based Analysis of Capacity Matching and Bottleneck Migration Along Evacuation Chains in Underground Commercial Complexes

Underground commercial complexes form a multi-stage evacuation chain linking horizontal transfer, vertical discharge, and exit allocation. Pathfinder simulations examined occupant-profile composition, stair width, corridor configuration, and pedestrian diversion through single-factor and coupled scenarios. Increasing stair width from 1.0 to 1.8 m reduced evacuation time by 39.9–45.7%, while marginal benefits declined beyond approximately 2.4 m. A segmented wide-to-narrow corridor reduced evacuation time from 207 to 119 s (42.5%). Balanced diversion reduced evacuation time by 25.3% in the symmetric layout, whereas the asymmetric optimum assigned 75% of occupants to the nearer exit and achieved a 25.8% reduction. Sequential stair-and-final-exit widening, corridor modification, and diversion reduced coupled-model evacuation time from 274 to 213 s (22.3%). The results support a system-level interpretation in which local capacity expansion can relieve one constraint while transferring the controlling bottleneck to a downstream segment. Because the analyses use prototype geometries under smoke-free conditions, the reported numerical values are model-specific diagnostic responses rather than universal design thresholds.