Study On The Computation Model Of Road Network Capacity In Small Mountainous Cities

In recent years,with the car ownership growing,traffic jams gradually spread from large and medium-sized cities in plain or coastal area to small mountainous cities.The main contradiction is the imbalance between traffic supply and demand.Within this context,investigate thoroughly the characteristics and supply capacity of the road network in small mountainous cities can provide a basis for solving the traffic problems of this kind of cities.However,the road network capacity that characterizing the traffic demand processing ability of small mountainous cities still needs to be improved according to its road and traffic characteristics.In this paper,the road network topology and the factors that affect the road network capacity are firstly discussed,and the influence mechanism of the road network own properties,the characteristics of urban traffic and traffic control on the road network capacity are expounded.And proceed from the above three aspects,this paper analyzes the road traffic characteristics of small mountainous cities such as road network characteristics,traffic travel characteristics and traffic management facilities,summed up the characteristics including relatively imperfect road cross-section composition,significant proportion of non-motor vehicle trips,relatively fixed traffic demand distribution,and an average travel time of less than 30 minutes.Secondly,the value of road network capacity is influenced by the traffic demand distribution and traffic distribution.The road impedance function determines the urban traffic distribution and then affects the road network capacity.In this regard,the traditional BPR model of road impedance function is modified according to the characteristics of imperfect road cross-section composition and large proportion of non-motorized vehicles,and the travel time modification model was proposed based on accumulative traffic flow analysis of mixed traffic road sections.Through the error comparison of measured data in same type of road,results indicate the traditional and modified BPR models respectively produce the average errors of 35.021%and 4.597%in travel time for arterial roads,and of 46.737%and 3.120%in travel time for access roads.It can be concluded that the estimation performance of the modified BPR model is better than that of the traditional BPR model.Finally,according to the road and traffic characteristics of small mountainous cities,the definition of small mountainous city road network capacity is proposed;On the basis of the modification of road impedance function in small mountainous cities,the process of traffic flow entering and exiting in different time periods is expressed by the accumulative traffic flow of road sections,and the road network capacity computation model for small mountainous cities is constructed.The upper section is road network capacity maximization model with capacity constraints,and the lower section is user equilibrium assignment model considering the inflow and outflow process of traffic flow.Based on the incremental assignment method two loading OD matrix,an algorithm is designed to solve this model.Through the distribution of current demand of road network in Songxi built-up area of Fujian province,the accuracy of the distribution in the model is verified.It is satisfactory that the errors in traffic assignment of most road sections are below 15%.Subsequently,the road network capacity of Songxi built-up area is computed to 4012 pcu for half an hour.Based on the bottleneck sections of road network which are distinguished by computation,the suggestions for improvement of road network are put forward.Compared with the traditional model,travel time modification model proposed in this paper is more suitable for road traffic states in small mountainous cities.The computation model and algorithm of road network capacity in small mountainous cities built in this paper takes full account of the road and traffic characteristics and the impact on road network capacity of small mountainous cities,which is more practical in the computation of road network capacity in such cities.