Research Of Subway Traffic Network Optimization Based On Space-time Accessibility

As the key of urban public transportation,the subway plays an important role in alleviating urban traffic congestion.There are many advantages to building developed subway network,such as punctuality,safety,comfort,convenience,and high economic benefits.It not only brings convenience to the residents' travel,but also improves the travel efficiency and service level in urban areas.It optimizes the city's travel service,improve passengers' travel conditions,and drive economic development along the site.With the people-oriented concept deeply rooted in people's minds,the time and space accessibility of residents' travel is even more important.In this paper,it focuses on the perspective of individual travel,and satisfies the expected travel time.The number of time-space unreachable OD is used as a measure in the subway network.By constructing the network optimization model,the Lagrangian relaxation algorithm is used to solve the model,which can provide route built proposes an optimization plan.This paper analyzes the relevant theories of subway network planning,which includes the functional positioning of the subway and the law of passenger flow operation,and studies and summarizes the scale and space structure of the subway.According to the distribution of important transportation hubs,passenger flow distribution points,transfer nodes and first and last stations of the city,distribution points are reasonably and orderly connected to facilitate the attraction of the subway to the passenger flow and increase the subway service level.A network optimization design model based on spatiotemporal accessibility is constructed.The network design problem is modeled as a linear integer programming model by introducing decision variables such as link selection variables and road construction variables.In order to maximize the overall time and space accessibility of the network as the optimization goal,under the condition of meeting the construction budget,find the optimal new line and join the existing network.The decision variables of the model include the road segment selection variables and the road segment construction variables.The constraint conditions include the space-time equilibrium flow constraint,the coupling constraint of the road segment to be built and the spacetime arc,and the construction budget constraint.This paper studies the algorithm for solving the network optimization model.First of all,the core ideas and basic forms of the Lagrangian relaxation method are expounded.By relaxing the complex constraints,the original problem is decomposed into subproblems,mainly the shortest path problem and the knapsack problem,which greatly reduces the difficulty of solving the original problem.As the Lagrangian relaxation problem expands the feasible domain of the understanding,there is a gap between the objective function value of the relaxation problem and the objective function value of the original problem.In order to narrow this gap,we solve the Lagrangian dual problem,update the complex constraint Lagrangian multiplier,shrink the feasible domain of the Lagrangian relaxation problem solution,and relax the relaxation problem and the original problem objective function value.The gap between them forces the solution of the dual problem to gradually approach the optimal solution of the original problem.According to Suzhou subway network,this paper verifies the feasibility of the model.Based on the already-operated lines 1,2 and 4,with the expected planning schemes for Lines 3 and 5 as the reference,under the premise of meeting the conditions of the network scale and construction cost,the new lines will get optimized.