Transportation network design is one of today’s vital concerns in transportation field. Optimization of transportation networks results in increasing the performance of the network which is one of the most challenging issues for scientists nowadays. Therefore executive and cost effective constrains as well as structural differences of road transportation emphasizes the essential importance of development and improvement in railway transportation.
Optimization and improvement of the network with respect to its structure, along with considering executive and financial constraints of railway networks, is among the raised issues of increasing the railroad share of the network (railroad share over demand). On the other hand, producers (!) are looking for the most suitable mode of transportation among the verity of choices for their delivery. Among the different competing types of transportation (rail and road), companies choose their transportation type with considering the advantages of the network they choose as well as with respect to their own priorities. Conception of this competitive field in real life and the effect of companies priority of choice in mathematical optimization model, is another credible feature of this research.
As introduced earlier, this research proposes two mathematical optimization models. In each model the capacity of two-way block-section in each direction is considered separately. In the first proposed model, the goal is to minimize the total travel time of the network and determine the optimum corridors for two-way implementation and upgrading the network. With considering the external costs of transporting merchandise, second model focuses on minimizing these costs and determines the optimum ways for construction, two-way implementation and electrification of the block sections.
With analyzing the Iranian Railroad Network data, the proposed models were implemented and with the use of CPLEX solution, these models were resolved. The study and analysis of the first model’s results indicate the required budget for improvement of railroad and the two-way implementation of the chosen corridors. The second model confirms the amount of prevented external costs in the case of using railroad transportation. This model determines the optimum corridors and defines the type (two-way implementation, electrifying, or both) of their improvement