In this chapter, the authors develop a container cargo assignment model on the intermodal international shipping network, including worldwide maritime network and regional land network. It was applied in Central America to several countries sharing a border, in order to simulate the impact of policies on port maintenance and other related logistics. The authors apply the same model by focusing on the Lower Mekong region and the route choice problem of the Cambodian international container cargo. The model is developed from the viewpoint of cargo owners. Each shipper is assumed to choose the ports to be used for export and import, given the freight charges for maritime and land transport, and shipping time, on the intermodal network, including both land and maritime shipping. Maritime shipping network is basically developed from the MDS database. From the MDS database, data are acquired not only on making the network, but also on vessel speed, average vessel capacity, and frequency of each service.