| In recent years,with the increasing number of motor vehicles in China’s cities,traffic congestion has become a normal problem in large and medium-sized cities.The road network structure of mountain cities is complex,and the land is usually divided into several clusters with a certain scale by mountains and rivers.Cities are usually built between large mountain areas with undulating terrain,and the road conditions are not so good as that in other cities.Among them,central business districts distributed within the cities form a core area where people and vehicles gather.The traffic control in the core area is difficult,and traffic congestion problems occur frequently.The essence of traffic congestion is the imbalance between traffic supply and demand.How to quantify the traffic supply and demand and improve the imbalance is the mainstream idea to solve the traffic congestion problem.This thesis starts with quantifying the road network supply capacity of mountain cities,and conducts relevant research around the road network capacity to provide theoretical support for solving the problem of traffic congestion in mountain cities.This thesis selects the mountain city CBD regional road network as the research object,analyzes the characteristics of mountain city CBD regional road network,and puts forward the definition of mountain city CBD regional road network capacity;Determine the main influencing factors of road network capacity in mountainous city CBD area;Based on the idea of cut set method,the problem of solving the road network capacity is transformed into the problem of solving the minimum cut set in the road network;The construction methods of estimating regional road network capacity of mountainous city CBD based on auxiliary map method and improved traffic assignment simulation method are proposed respectively;Chongqing Guanyinqiao CBD and surrounding road network are selected for example verification.The specific research contents are as follows:(1)Study on influencing factors of road network capacity in mountainous city CBD area.This thesis selects characteristic indicators from three aspects of road conditions,traffic modes and traffic control,analyzes the differences between mountain city and plain city CBD road traffic,finds that mountain city CBD regional road network has significant characteristic differences in these three aspects,and puts forward the definition of mountain city CBD regional road network capacity from the perspective of narrow road network capacity;Based on the Delphi method,statistical experts use the importance coefficient and dispersion coefficient to judge the rationality of the indicators for the scoring data of characteristic indicators;The weight of effective indicators is determined by using the analytic hierarchy process(AHP).Finally,five indicators,including intersection control mode,openings along the road,number of lanes,intersection spacing,and lane width,are selected as the main influencing factors of the road network capacity in the mountainous city CBD area.(2)Research on the capacity estimation model of mountain city CBD regional road network based on cut set method.In view of the limitations of cut set method,this thesis proposes a road network capacity estimation model based on auxiliary graph method and a road network capacity estimation model based on improved traffic assignment simulation method,and obtains the road network capacity through comparison.In order to reflect the actual road capacity of mountainous cities more accurately,the capacity model is revised in combination with the main factors affecting the capacity of mountainous cities’ CBD regional road network when building the capacity estimation model of mountainous cities’ CBD regional road network based on the auxiliary map method;In order to improve the auxiliary graph method,which can not solve the minimum cut set problem under multiple OD pairs,a method is proposed to abstract multiple OD pairs in the road network into a group of OD pairs,and further solve the road network capacity by using the auxiliary graph method.(3)Based on the improved traffic assignment simulation method,the research on the estimation model of the regional road network capacity of mountain city CBD.In order to achieve a more suitable traffic volume allocation for actual traveler route selection,this thesis improves the traffic allocation simulation method from two aspects: calibrating the road resistance function in mountainous city CBD area and proposing the minimum cut set judgment standard.In order to accurately simulate the traffic volume distribution of the road network,it is necessary to accurately master the road resistance function of each section.By studying the relationship between road resistance and traffic load,the road resistance function after each distribution is modified to make the distribution of road network flow more reasonable;Based on the principle of traffic simulation method,the judgment standard of the minimum cut set of regional road network is constructed,and the capacity estimation model of mountain city CBD regional road network based on the improved traffic assignment simulation method is further obtained.(4)Instance validation.Chongqing Guanyinqiao CBD and surrounding road network are selected as the research object.The auxiliary graph method is used to solve the road network capacity based on the road section capacity data,and the result is 30137 pcu/h.Using the improved traffic assignment simulation method,based on the OD traffic volume data between traffic zones,the outlet network capacity is 38,776 pcu/h.The road network capacity results obtained by the two methods are analyzed.The results obtained by the auxiliary graph method are set as the lower limit of the road network capacity,and the results obtained by the improved traffic assignment simulation method are set as the upper limit of the road network capacity.The principles and purposes of the two methods are different.In the process of practical application,these two methods can be selected in combination with the specific conditions of the problems studied. |
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