Sustainable Rural Road Network Planning Under Hierarchical Constraints in Complex Mountainous Terrain: A Case Study of Zhangjiachuan Hui Autonomous County, China

Rural road planning in mountainous areas must coordinate existing-road use, hierarchical connectivity, and construction requirements. This study proposes a network generation method integrating existing-road topology with roadless space through a hexagonal occupancy grid. Existing-road neighborhood and cross-neighborhood edges represent different access characteristics. Sequential rules generate a county-level backbone, township-level links, and village-level access, while identifying reuse, upgrading, and new construction. Six scenarios are compared in Zhangjiachuan Hui Autonomous County, Gansu, China. The proposed scenario generates an 880.001 km network, with existing roads accounting for 94.53%. New construction totals 48.128 km, 85.63% less than under uniform cross-neighborhood representation. Mean shortest travel times for village-to-township government, township government-to-county seat, and village-to-county seat connections decrease by 15.65%, 37.85%, and 27.91%, respectively, relative to the pre-planning network. All three hierarchical compliance rates reach 100%. The proposed scenario achieves the highest composite score among the six scenarios under the specified indicators and weights, balancing existing-road use, service accessibility, and construction requirements. The method supports preliminary network layouts and scenario comparison in mountainous counties with comparable terrain and road data.