Theory And Methods For Adjusting The Diversion Of Freight Flow Between Highway And Railway Network Considering Carbon Emissions

As the problem of air pollution is becoming increasingly severe,developing low-carbon economy has attracted widely attention from the international community.For China,in order to accord with the international action and promote the continuable development of our economy and society,the governments pay much attention to carbon emissions reduction.Among the many sources of carbon emissions,the transportation industry is a large one.Thus,promoting the development of low-carbon transport will greatly benefit the carbon emissions reduction.Compared to highway transport,railway is better choice for developing green transportation because of its large volume and low carbon emissions.Therefore,increasing the share ratio of railway workload in the transportation system is an effective way to optimize the transportation structure and develop low-carbon transportation.However,in practice,since the relative policy and the optimization of transportation resource allocation are not enough,there is still much long distance freight flow which is suitable for railway transportation goes through highway.This causes that the proportion of freight flow distribution between railway and highway network deviates from the optimal one,and the load of some highway section and carbon emissions are higher than expection.Thus,designing adjusting measures to divert some freight flow from highway to railway is an important problem.Nonetheless,in theory,the research for this problem is insufficient.Hence,by referring to the existing achievements and considering the characteristics of railway and highway transport,this paper made deep research and discussion on the theory and methods for adjusting the diversion of freight flow between highway and railway network under the background of low-carbon emissions.The main contexts are shown as follows:1)Firstly,the difference between railway and highway freight transport is analyzed based on their current situations and operation modes.Then the mechanism of forming the distribution of freight flow on railway and highway network is analyzed according to the participants in the freight transportation and the related processes.Furtherly,the reason of the unreasonable distribution of freight flow on railway and highway network is studied.Based on the study,the basic strategy which contains two aspects is put forward.The first one is guiding the shippers changing their mode choices and the second one is optimizing the allocation of transportation resources.2)Based on the mechanism of forming the distribution of freight flow on railway and highway network,the method based on mathematical programming for calculating the freight flow distribution on railway and highway network under certain situation is designed.The method includes calculating the transportation demand OD based on shippers' mode choices,calculating the freight flow distribution on railway network,calculating the infeasible flow of railway,modifying the demand OD of highway network,freight flow assignment on highway network and so on.The linearization method for the non-linear flow assignment model is also developed.3)According to the externalities and internalizing externalities theory in the field of economics,the carbon-tax-based measure is designed to adjust the transportation demand of railway and highway.Thus the environmental cost is correlated with the shippers' benefit and it can influence the shippers' mode choice behavior.Then,based on the measure,the models for calculating the freight flow distribution are modified.Finally,the quantitative effect of the measure is studied with the method of sensitivity analysis.4)To address the problem that the diversion is restricted by the bottleneck section in railway network,the strategy of diverting part of the journey of the freight flow from highway to railway by multi-modal transportation is put forward.Then,based on the general network which contains highway transportation,railway transportation,transferring,loading and unloading,the mathematical model of optimizing the multi-modal plan is put forward.The model considers the carbon tax and traffic congestion cost as well as the basic travel time and expenditure cost.A linearization method is also introduced to transfer the non-linear model into a linear one so that the model is easy to solve.The effect of implementing multi-model transportation on the total carbon emissions is also analyzed quantitatively.5)To reduce the negative influence of bottleneck section in railway network on diverting freight flow from highway to railway,the method of diverting some railway freight flow on full-loaded section to non-shortest path to release more capacity to attract more freight flow from highway is studied.For this,the mixed integer programming model for railway freight flow assignment which considers infeasible flow is established.In order to coordinate the object of maximizing the diversion between railway and highway and minimizing the total transportation cost of railway,the model take maximizing the total profit(including carbon tax)of railway as the objective function.In terms of the constraints,the no-split rule of single freight flow,and detour ration restriction are considered.For the non-linear item in the model,the method of employing assistant decision variables and formulating assistant constraints is put forward to linearize it.Finally,the quantitative effect of optimized railway freight routing plan on the diversion of freight flow between railway and highway is analyzed according to the solution of the model.6)To address the problem that there may still be bottlenecks which restrict the diversion in railway network after optimizing the operation plan,the railway network plan model is studied.In order to describe the influence caused by the change of railway network structure on shippers' mode choice,the model is formulated as a bi-level programming one.The upper level is for railway network improve decision and freight flow assignment,and the lower level is for calculating the shortest path after the railway structure is changed and modifying the transportation mode split.Then,based on the character of the model,a two-stage strategy is designed to solve the model.Based on the solution of the model,the method of formulating integrated objective function which considers carbon emissions is developed to analyze the impact of considering carbon emissions on the final decision.This paper studied the basic principle and main idea for diverting freight flow from highway to railway from several aspects,and developed mathematical model for the related optimization problem.The quantitative methods for analyzing the adjusting methods are put forward based on the case studies.The above achievements will provide theoretical reference for the policy study of related decision makers.