In rail transportation networks, the high demand of cargo to transport from the origins to different destinations, along with the capacity limitation of the corridors would have created a substantial concern for the system operators in optimizing usage pattern of the rail infrastructure and prioritizing OD-commodity tuples of the network. In the present study, a novel approach for freight flow policy-making in the rail transportation networks, with focus on determination of the prioritized origin-destinations is presented. In this approach, two objectives, including maximizing total revenue of the rail company and maximizing portion of rail demand, are applied. The approach consists of two parts. In the first part, due to the capacity limitation of the railway corridors, the demand of the OD-commodity tuples of the network, and the cost of transporting different goods, we analyze the priority of the OD-commodity tuples to occupy the capacity of the corridors, and accordingly, the maximum railway revenue is calculated. In the second part, a new approach is proposed as a government policy to allocate subsidy, with simultaneous consideration of railway revenue management, portion of rail transportation market, and external costs reduction. In order to solve the problem defined in the present study, a bi-objective linear programming model has been developed. The output of the model determines the optimal economic pattern of freight flow in the railway network, based on the maximum revenue of the network operator along with maximization of rail demand portion. The proposed mathematical model has been implemented for the Iranian railway network. Also, in order to increase the portion of the railway system, different scenarios for promoting the corridors’ capacity have been examined and their results have been eva‎luated based on the imposed external costs. According to the results of the present study, the competitive nature of rail and road transportation modes would cause restriction of increasing railway network revenue. Hence, we can determine a specific value of the increase of rail transportation prices as the optimal point at which the highest railway revenue is obtained. In addition, with a gradual increase in the capacity of the railway block sections, the railway revenue increases; however, the rate of this increase would reduce. Although the choice of OD-commodity tuples with more profit demands leads to higher rail revenues, the results show that this will not always be true. So, according to the mentioned result and based on prioritization of the OD-commodity tuples to pass through the network, a new concept so called "Economic Capacity" can be developed for each block section. Accordingly, prioritizing the OD-commodity tuples in passing through a railway network is assessed based on the economic capacity of the block sections of that network. the priority of OD-commodity tuples in the proposed model for the first problem in the Iran railway network and according to the predicted demand in 2035, the accepted demand for railways than the existing demand will increase by about 21.5%. Also, in the present study, an effective method for calculating the governmental subsidy granted to the green rail transportation mode is presented. The method, not only maximizes the railway revenue, but also significantly reduces the external costs imposed on the entire rail and road transportation systems. The research findings provide an appropriate tool for the managers and policy makers to determine the optimal pattern of capacity allocation in railway transportation network.

محمد تمنايي، رامين جوادي

احمد رضا جعفريان مقدم، حسين حق شناس