Capacity Analysis Of Signalized Intersections Under Mixed Traffic Conditions Based On The First Discharge Headway

Mixed traffic is one of the main characters of China's urban traffic.It often causes signalized intersections to be out of order and the control systems with low efficiencies.The intersection capacities are declined as well.With the high-density mixed traffic conditions and checkerboard layout of road network,some fine traffic theories and methods of developed countries cannot be directly applied in Beijing's road traffic system.In view of the traffic characteristics of metropolis including Beijing city, the current study focuses on the signalized intersection capacity under mixed traffic conditions,modifies the existing model using the first discharge headway,and estimates the parameters in the model.In view of the domestic and international research status on signalized intersection capacity,the study analyzes the traffic characters of Beijing city with investigation and data collection.The existing model is modified by determining the first discharge headway.The main work of the study is as following:(1) Analysis of the traffic composition and interference ratio of different lanes.In different intersections,the first discharge headways of different vehicle types are analyzed by lanes(left-turning lanes,inside through lanes,and outside through lanes). The difference of the first discharge headways is mainly determined by the traffic flow composition,type of interference,and the drivers' actions in response to traffic lights.Referring to the traffic composition in different lanes,the outside lanes always hold more large-sized vehicles,especially buses.The number of cars is larger in left-turning lanes than through lanes.In the case of interference,vehicles in left-turning lanes suffer much serious interference than through lanes,and the outside lanes receive much interference than inside lanes.The main interference came form non-motor vehicles and pedestrians.(2) Modeling the first discharge headway model of different lanes.With data analysis and model fitting,the functions of the first discharge headway of the left-turning lanes,inside through lanes,and outside through lanes are demonstrated to be Logistic model,Compertz model,and Logsitic model,respectively.By further calculation,the first discharge headways of the left-turning lanes,inside through lanes, and outside through lanes are 3.98 s,4.60 s,4.85 s,respectively.The modified first discharge headway has a high increase as 100%than before. The modified first discharge headways increase from left-turning lanes,inside through lanes,to outside through lanes,which indicates that the outside lanes often suffer the interference more easily.(3) Error comparison of modified capacity model and the traditional one.The errors of modified capacity model and the traditional one are calculated out using the actual data of five intersections.The error of modified model decreases sharply than the traditional one.Referring to the capacity calculation of the whole intersection,the error decrease from 8.61%to 4.45%,which located in a fine confidence interval.