Study On Freight Flow Distribution In Certain Railway Network With New Lines

In order to implement the national decision of increasing investment to railway construction and expanding freight transport demand, a lot of new railway lines are built efficiently and orderly. However, freight flow distribution in certain network with new lines is mainly through manual adjustment and qualitative forecasting currently, which confronts great difficulty in computational efficiency and forecasting accuracy. Therefore, it is significantly important to study freight flow distribution in certain network with new lines. Freight flow forecasting in railway design departments can be divided into two parts:one is forecasting newly induced freight flows from neighborhood; the other is forecasting transferred freight flows from neighbor rail lines. This paper chooses the second part to study.Firstly, based on the influencing factors analysis, Bi-level programming model of regional freight flow distribution is proposed, in which individual optimum for single freight flow and global optimum for all freight flow are taken into account. Specifically, interactive mechanism between freight flow distribution in certain network (the upper layer) and route choice of single freight flow (the lower layer) is explored, and the relationship between principal and subordinate in Bi-level programming model is considered as well. Then, global optimum for all freight flow is taken as the primary goal and individual optimum for single freight flow is employed as the secondary goal. In this way, the system optimum of freight flow assignment with new lines opening is achieved.Secondly, solution algorithm is put forward for the bi-level model. For "big to small for same kind freight flow and exploring shortest route", freight flow is distributed on the basis of individual attribute, and the larger freight flow is given priority to choose shortest route. With regard to "distribution based on least impedance and adjustment according impedance factor", interval or station impedance is enlarged, so part freight flow of saturating interval or station is distributed to the sub-optimal route, which makes freight flow within the capacity and minimizes the freight turn-round flow. Since the latter algorithm has high timeliness and good convergence, meanwhile, the algorithm limitation has little effect on the result and the effect can be reduced through decreasing the impedance value, it is applied in the software development.Finally, regional freight flow distribution software is developed, which can achieve dynamic adjustment and fast computation of freight flow distribution. Therefore, theoretical support can be provided to the analysis and decision for relevant departments. Qinglian Line is taken for example. Through the software, the influence of Qinglian Line on freight flow distribution in neighborhood network is analyzed. The result indicates consistency across the function position of Qinglian Line, which verifies the validity and applicability of the proposed model and algorithm.In addition, on the basis of freight transport demand, freight flow is first classified into four types and distribution order of each type is confirmed. Then, each type of freight flow is distributed respectively, which satisfies the route demand of each freight flow to a great extent within the limited capacity and achieves the global optimum. If there is no classification data of freight flow, freight flow can be taken as the same type and the solution approach stays unchanged.