Study On Practical Method For Optimization Of Multi-level Bus Network In Megacities

Under the context of acceleration of urbanization process and in the face of problems in the city transportation such as intensified traffic congestion,frequent occurrence of traffic accidents,deteriorated urban environment and grave energy consumption,due to rapid economic development and constant growth of ownership of private cars,sustainable development of megalopolis can be achieved only if the development of public transportation is prioritized and the road of Transit City is followed.In recent years,the construction of rail transit and bus rapid transit has been also accelerated and the service level of public transportation has been improved.But with the rapid growth of proportion of mobility by cars,the operational environment of group public transportation is getting worse and worse,especially in megacities,and in the context of expansion of city sizes and diversification of mobility requirements,with its existing network layout,ground public transportation is hard to adapt to needs in a new period and even suffers from the impact from new public transportation modes like public bikes and shared bikes,leading to continuous decrease in passenger flow and share rate,and under the new situation,conventional ground public transportation enters a new period when changes are urgently needed.This paper outlines the new location of ground public transportation in a new period from the perspective of the relationship between demand and supply by analyzing the mobility characteristics and public transportation system functions of megacities,proposes a new idea taking Transit City as a guidance,establishment of an "open,diversified,integrated” public transportation system as an aim,and with “service via a single network”,studies the problem of optimization of ground public transportation network of megacities based on the initial formation of rail transit network,fully considers the shifting of functional location of ground public transportation after the networking of rail transit,and builds optimization modes and arrangement methods on the principle of “zoning and delamination ” from an angle of overall mobility chain.First,this paper starts with analysis of mobility requirements for public transportation in megacities,analyzes the requirements of megacities of megacities in three aspects of city size and spatial form,urban transportation structures and passenger needs respectively,manages changes in mobility characteristics of megacities,studies the interactive relationship between the trend of those changes and public transportation and sorts demand basis for the functional structure of public transportation system in megacities.Second,this paper studies the function mechanism and development demand of public transportation network on the basis of demand analysis,proposes a construction requirement of the development of Transit City oriented public transportation system,relocates ground public transportation needs though characteristic analysis of subsystems of public transportation,with "service via a single network" and from the perspective of the whole process of mobility,puts forward a new idea of networking of multi-level ground public transportation for passenger flow needs,points out two important directions for optimization of ground public transportation at the present stage: integrated development with ground public transportation network and hierarchical function arrangement for its own network structure.Next,this paper analyzes the structural characteristics of ground public transportation network in megacities based on functional location of ground public transportation,studies the structural relationship between ground transportation network and rail transit network as well as the hierarchical relationship within conventional ground public transportation systems themselves,proposes an idea and a method for the zoning of public transportation service and hierarchical division of ground public transportation network function,simultaneously analyzes the topological relation between ground public transportation network and rail transit network,divided ground public transportation routes into parallel collection,joint collection and non-related collection with rail network,and brings up a determination method for parallel collection and joint collection as well as network characteristics of integration of two networks at different stages.Finally,this paper proposes an optimization method and checking examples based on rail transit network,gives a generation algorithm of optimized candidate routes for routes with parallel relationship and non-related relationship formed by ground public transportation and rail transit in topological relation with respect to the integrated network of rail transit and ground public transportation and based on the hierarchical indexes of ground public transportation;on this basis,the paper establishes a multi-purpose optimization model taking into account not only customer interest but also corporate benefits,performs mathematical calculations by taking West-Mid Rive and Northern Region of Nanjing as an example,and explains the practical value and meaning of researches.