Railway-Integrated Planning of Electric Vertical Takeoff and Landing Aircraft (eVTOL) Vertiports

Electric vertical takeoff and landing (eVTOL) aircraft provide a new and more sustainable form of mobility for passengers. In regional transport, eVTOL services can complement existing railway systems by providing direct air connections for selected trips. However, the practical value of eVTOL services is subject to strict infrastructure requirements beyond aircraft performance. Consequently, strategic vertiport deployment and charging capacity must be embedded into existing transport networks rather than planned as standalone systems. To achieve this objective, this paper presents a strategic railway-integrated planning framework for eVTOL vertiports and charging capacity. The framework treats railway stations as multimodal access nodes and leverages air links to selectively complement rail travel. It simultaneously optimizes siting, pad capacity, charging capacity, flight frequency, and fleet scale under infrastructure and operating constraints. To balance assignment fidelity and tractability in the integrated railway and air network, the framework applies a multicommodity flow (MCF) formulation for detailed network assignment and proposes a structured one-hop (SOH) formulation as a compact approximation. SOH restricts each substituted trip to a simple railway-air-rail (RAR) travel pattern with one direct air segment, thereby avoiding repeated intermodal transfers. Finally, the proposed framework is applied to scenario-based planning on a real-world railway network in Guangdong, China. The results show that all 11 sites selected by MCF are also selected by SOH, while SOH selects one additional site. The daily planning benefits obtained by MCF and SOH are 41,428 and 41,257 CNY/day, respectively, differing by only 0.4%, whereas SOH uses 93.5% fewer variables and reduces the solution time by 95.0%. Sensitivity analysis shows that no vertiport is selected when the transferable demand ratio is 1%. As the transferable demand ratio increases, both the planning benefit and the selected vertiport network increase until the site limit is reached.