The ever increasing need of developing efficient solutions for the transport of cargo, able to reduce transport costs while complying to green policies has promoted the use of multimodal transport during the last decades. Multimodal transport consists of the use of at least two modes of transportation for the transport of cargo from origin to destination. Governments and transport authorities (network planners) seek to make the optimal investment decisions when choosing where to allocate their budgets. To accomplish this they need to predict the response of the formulated policies on the cargo flow distributions over a multimodal network. Cargo flows over a multimodal network are in turn dependent on the behavior of water and land transport companies (network users), aiming in minimizing their own total costs of transportation. This research has developed a Decision Support Tool that is able to model cargo flows over a multimodal network, and predict the changes of cargo flows as a response to network planners policies. The research has used the freight transport network of Brazil as a testing ground for the model, and focused on improvements on the railway infrastructure. The results of the model suggest that the establishment of new railway connections and higher railway operating speeds can reduce the total costs and environmental footprint of transportation over a multi modal network. Finally, according to the model assumptions, it was concluded network users have a preference towards faster railway services.