Modeling the railway network design problem: A novel approach to considering carbon emissions reduction

- To take the environmental benefit of building railways into consideration when designing railway network, we developed a bi-level 0-1 programming model to balance the investment, transportation cost and environmental cost.
- To avoid the error caused by neglecting the empty car flows when estimating the railway network's utilization ratio, we modified the O-D matrix by adding the equivalent virtual freight flows according to the distribution of empty cars.
- Railway network design usually focuses on corridors that consist of several links. Since the links in one corridor mostly need to be same-level, we made the model practical by considering the relevance of the links in one corridor.
- Based on a numerical analysis, we find that the pattern of the planned railway network is influenced significantly by the weight coefficient of carbon emissions.

In recent years, air pollution has become a severe environmental problem. Many countries are seeking effective methods to reduce carbon emissions. Among the sources of air pollution, the transportation industry is a large one. Thus, developing low carbon emissions transportation is a new trend. Since railway transport possesses the advantages of high volume and low emissions, a new idea for transportation development is to divert truck freights to railway by improving the capacity of the railway. Based on this situation, this paper analyzes the carbon emissions of railway and highway transport and estimates the environmental benefit of building a railway. Next, a bi-level programming model for railway network design is recommended. Different from the classical model, the opportunity cost and carbon emissions of the infeasible flows, which cannot be transported by railway and will be served by highway, are considered in the objective function, enabling the model to balance the investment and carbon emissions. To comply with the practice of railway planning, we introduced the method to deal with passenger flow, empty car flow and relationships among the links in a corridor. In the end, a numerical example is conducted to test the model and compare the final decisions when different weights are set on the carbon emissions.