Factors Influencing Green Construction Costs of High-Speed Railways in Mountainous Areas Based on DEMATEL-ISM

As China’s high-speed railway construction extends deeper into the karst mountainous regions of the southwest, and as engineering construction faces rigid requirements for green and low-carbon transformation under the dual-carbon goals, green construction cost management for mountainous high-speed railways is subject to distinctive constraints and challenges that differ substantially from those of plain-terrain projects. Existing research on railway green construction costs has focused mainly on plain-terrain scenarios and has emphasized independent evaluations of how individual factors affect costs, while insufficiently revealing the coupled transmission relationships and hierarchical structures of cost-influencing factors in complex mountainous terrain. Consequently, management countermeasures often lack precise correspondence with influencing factors, and research conclusions show limited scenario adaptability and practical guidance value. To address these gaps, this study examines the construction phase of the karst mountainous section of the Guiyang–Nanning High-Speed Railway (G-N HSR). Through three rounds of screening—policy benchmarking, literature review, and expert consultation—a green construction cost influencing factor system comprising 20 indicators across five dimensions (external environment, technology, management, resources, and environmental protection) is established. A coupled model combining the Decision-Making Trial and Evaluation Laboratory (DEMATEL) and Interpretive Structural Modeling (ISM) methods is introduced for systematic analysis. Compared with existing studies, this paper makes three differentiated contributions. First, it is grounded in the complex karst mountainous research scenario and fully incorporates constraints specific to mountainous terrain, such as geological complexity, ecological sensitivity, and logistical limitations. Second, it overcomes the limitations of traditional independent single-factor analysis by revealing the hierarchical transmission logic and cost formation mechanisms among factors from a systemic perspective. Third, it establishes a precise correspondence between influencing factor hierarchies and management strategies, thereby avoiding broadly empirical engineering countermeasures. The results indicate that policies and regulations constitute the most fundamental driving factor, with a centrality degree of 2.006 and a cause degree of 1.745. The constructed five-dimension indicator system demonstrates good structural validity, with a cumulative variance explanation rate of 72.35% in exploratory factor analysis. Finally, the study delineates a three-level cost transmission hierarchy comprising a fundamental driving layer, an intermediate transmission layer, and a surface result layer. On this basis, it proposes hierarchical and targeted management countermeasures that can provide theoretical support and practical reference for refined green construction cost management of high-speed railways in southwestern mountainous regions.