This article analyzes an intermodal transportation network for international container cargoes in Korea. The actual transportation situation in Korea is formulated by a linear programming model. The model is validated first by comparing the model output with actual performance, and then the model is extended by incorporating various externalities arising from inland transport modes such as air pollution, congestion, accidents, noise pollution, and wear and tear. Moreover, the model is extended for assessing the effects of complying with carbon taxation and emission trading schemes, which loom large in international shipping communities. Test results of the models using the data obtained from reliable sources are presented and policy directions are discussed from an environmental perspective.