This paper develops a dynamic freight network simulation-assignment platform for the analysis of multiproduct intermodal freight transportation systems. At the core of the platform is a model framework for the mode-path assignment problem in multimodal freight transportation networks. The framework consists of three main components: a multi-modal freight network simulation component, a multimodal freight assignment component, and a multiple product intermodal shortest path procedure. The freight network simulation component incorporates a bulk queuing model to evaluate transfer delay experienced by shipments at intermodal transfer terminals, classification yards, and ports. The multimodal freight assignment component determines the network flow pattern from a mode-path alternative set calculated by the multiple product intermodal shortest path procedure, based on the link travel costs and node transfer delays from the multimodal freight network simulation component. This model can represent individual shipment mode-path choice behavior, consolidation policy, conveyance link moving, and individual shipment terminal transfer in an iterative solution framework.