The design of a hierarchical transportation network with transshipment facilities

In this paper an integer linear program is formulated to identify the least cost two-level hierarchical network. This network must include a primary path from a predetermined starting node to a predetermined terminus node. In addition, each node not on the primary path must be connected to some node on that path via a secondary path. Transshipment facilities are required at the intersections of the primary and secondary paths. Consequently, the formulation directly considers the number and locations of transshipment facilities in determining the minimal cost network. A heuristic is presented which employs a K Shortest Path algorithm and a Minimum Spanning Tree algorithm. Heuristic results of two sample problems are presented and compared to the results obtained by solving the integer LP formulation.