Observing the literature, still many opportunities for future research exist. Capacity limitation on links and hubs is a first example. Capacity in consolidation systems causes significant congestion at hubs. Inclusion of congestion in hub location problems leads to more balanced distribution of flows throughout the network and decrease the operational costs of the crowded hubs. Elhedhli and Hu, 2010, Rodríguez et al., 2007 and Ishfaq and Sox, 2012 model the service at a given hub as queueing networks and include the congestion as the flow beyond the capacity. These are the few cases explicitly considering congestion leading to an interesting research direction in studying high-volume capacitated systems.