Designing Hub Networks with Connected and Isolated Hubs

Modern supply chains depend on efficient, reliable and extensive freight transportation systems. Many of these systems utilize hub-and-spoke networks to provide transport between many origins and many destinations. These networks include hub facilities that provide a connecting, sorting and consolidation function which concentrates flows on the inter-hub links, called hub arcs, to exploit the economies of scale in transportation. This paper addresses the design of time definite hub and spoke networks using both connected hubs, that are adjacent to the hub arcs, and isolated hubs, that are not adjacent to any hub arcs. It also highlights the role of isolated hubs in expanding networks. Computational results are provided for time definite trucking in North America and the results demonstrate the role and the value of isolated hubs.