Analysis of Transportation Hypernetwork Robustness Based on the Internal Structure of Hyperedges: A Case Study of China’s High-Speed Railway

China’s High-Speed Railway (HSR), the world’s largest HSR system and a core component of national transportation, exhibits vulnerability in operational robustness to uncertain events such as natural disasters. Existing hypernetwork-based studies on HSR robustness often assume full connections among nodes within hyperedges, an assumption that deviates from reality. Using China’s HSR line and station data, this paper constructs a real-world HSR hypernetwork and three reconstructed hypernetworks with distinct internal hyperedge structures. It also proposes a cascading failure model accounting for internal hyperedge structures and quantifies economic feasibility through an optimization cost index. Experimental results show the real-world HSR hypernetwork has scale-free properties. Sub-line density within hyperedges shows a positive correlation with robustness, where denser sub-lines enhance robustness. Prioritizing sub-line deployment around hub stations offers the most economical solution. This paper is the first to provide an HSR hypernetwork robustness optimization scheme from the perspective of internal hyperedge structures, offering theoretical reference for research on transportation networks with similar topological characteristics.