Routing Traffic at Hub Facilities

Flows arriving at a hub or a transshipment facility may need to be switched from one path to another to complete their journey. These transfer aspects of hub and spoke systems are widely recognized as a hindrance to efficient completion of transit trips. For example, time-consuming delays at transfer points for bus passengers are a major reason for poor levels of service between some nodes when the origin and destination are on different network lines. Such transfers also arise in multimodal interaction systems. This paper outlines a simple notation and analytical framework for optimizing flows within a hub (i.e. at nodes with transfers) and discusses several variants of the problem. This paper addresses prototype models for the efficient allocation of resources to facilitate the operation of interactions at the hub. The paper is primarily a conceptual and methodological overview, but well-recognized existing optimization models are suggested as being useful for some of the related tasks. Small numerical examples are used to illustrate some of the ideas.