Vertiport siting and UAM network design with eVTOL performance: An MILP for direct-transfer mode choice

To support early urban air mobility (UAM) deployment, this study develops an integrated planning framework for vertiport-centered network design. The framework is formulated as a mixed-integer linear program (MILP) that co-optimizes vertiport siting and capacity, direct and transfer services, fleet scheduling, and network flow balance, while endogenizing discrete eVTOL performance profiles and coupling vehicle-level energy feasibility with network routing and service decisions. A case study of Guangzhou shows that direct and transfer services play complementary roles in shaping network efficiency. Direct services dominate high-demand corridors, whereas transfer itineraries (i) extend connectivity and enable peripheral-to-peripheral accessibility and (ii) on selected long-distance corridors, yield efficiency gains by splitting long constrained legs to avoid endurance-induced cruise-speed reductions, thereby increasing effective travel speed with limited geometric detours. The optimized network is self-balancing with no empty repositioning flights, as passenger-carrying multi-leg itineraries implicitly absorb the balancing movements that would otherwise require deadheading. Despite system-level door-to-door time advantages, first- and last-mile access and in-vertiport processes remain the dominant bottlenecks, with effective flight time contributing approximately 10–30% of door-to-door time. Deployment feasibility is highly sensitive to operating-altitude standards: raising the safety altitude from 150 m to 300 m sharply reduces route feasibility under baseline battery technology, whereas a 25% increase in specific energy preserves 43.7% of the baseline route availability at 300 m while maintaining high cruise speeds. These findings underscore the value of system-level co-optimization of infrastructure, operations, and vehicle performance, and the necessity of evaluating deployment policies in light of plausible technology trajectories, especially near-term improvements in energy storage.