Study On The Traffic Efficiency Of Urban Underground Fast Channel Under Uncertain Demand

With the rapid development of China’s cities,citizens have higher requirements for inter-regional travel time.In order to meet the needs of citizens,large cities which are limited by land use,rivers,lakes,seas,mountains and other restrictions,increasingly favor the construction of urban underground fast channel.The current research on the planning of urban underground fast channel only considers the traffic demand in a static and single state without considering the uncertainty of the actual traffic demand,which may easily lead to local congestion of urban underground fast channel and reduce the traffic efficiency of the whole underground channel.Based on this,considering the uncertainty of demand,the traffic efficiency of urban underground fast channel under uncertain demand is studied,so as to ensure the full utilization of the traffic efficiency of underground channel.According to the meaning and traffic characteristics of urban underground fast channel,the relationship of surrounding road network OD and underground channel traffic demand is analyzed.By researching the sources and influencing factors of underground channel traffic demand uncertainty,this paper find that land use change can cause lasting change of traffic demand and has a long-term effect on uncertainty.In engineering practice,people usually consider daily demand status.So mainly considering uncertainty on the direction and number influenced by land use change,track the traffic source area of underground channel exit,then combining the source area’s land use uncertain situation,analysis the direction uncertainty demand of underground tunnel;in order to adapt to the lack of historical data,discrete distribution model and subjective probability method are selected to construct the model of the quantitative uncertainty of traffic demand.In addition,a method to analyze the traffic efficiency of underground channel is proposed with single OD uncertainty and multiple OD uncertainty.According to the traffic function(quickness,long distance and large volumes)of underground channel,put forward the traffic efficiency measure index: turnover and passing rate respectively in the form of absolute and relative form measure underground tunnel’s service efficiency,delay and average maximum queue length respectively from the angle of time and space,measure the quickness of underground tunnel,which can meet the demand of road users and administrators at the same time.According to the characteristics of underground traffic,the microscopic analysis model of underground channel is constructed to obtain the traffic efficiency index.Taking the Lianghu Tunnel in Wuhan as an example,a traffic demand uncertainty model with the minimum exit capacity was constructed,and the change of traffic efficiency under uncertain traffic demand was analyzed.According to the traffic efficiency index,it is found that the local congestion in the intersecting area of the Lianghu Tunnel reduces the whole traffic efficiency.Based on this,an optimal scheme for the extended interleaving zone is proposed and it is found that the optimal scheme has higher traffic efficiency under various traffic demand.In this paper,a set of content and method system of uncertainty analysis of traffic demand for urban underground fast channel is proposed for engineering practice,which provides reference for the planning,design and optimization of underground channel,so as to make full use of the traffic efficiency of urban underground fast channel and give play to its traffic service function.