Research On The Location Of U-turn Openings At Urban Signalized Intersections

As the important means to ensure the traffic operations smoothly and orderly,the U-turn organizations,which generally including the road U-turn opening and the intersection U-turn opening two forms,have been widely applied.As the increasing U-turn demands,thanks to the advantages in traffic flow organization and security,the intersection U-turn opening organization has currently become the main application mode of urban road network.Currently,due to the lack of design standards for the location of U-turn openings,many traffic engineers are usually based on their experiences to make design schemes.Because of this phenomenon,the mutual influences between the left-turn vehicles and U-turn vehicles are becoming more and more serious,and the U-turn organization efficiency cannot be fully utilized,at last the efficiency of the intersection has been decreased.Thus,according to the signalized intersection U-turn demands,maximizing traffic efficiency is regarded as the goal to research the intersection U-turn opening location.The main research contents include the following sections:Firstly,the U-turn demands and organization methods of the signalized intersections are researched.The source of the intersection U-turn demands and the operational characteristics of U-turn vehicles are analyzed.Then the various common design patterns of U-turn organization and various signal control methods are summarized.On the basis of those,the research objects of this paper are determined.Secondly,the location of U-turn openings at intersections with single left-turn lane is researched.The loss time model of the left-turn and U-turn shared lane is first established.Based on that,the mutual influence mechanism between the U-turn vehicles and left-turn vehicles on the shared lane under different traffic conditions are revealed.Then combined the vehicles arrive rates and the probability distribution function of vehicles with different directions,the traffic capacity calculation model of the left-turn and U-turn shared lane is established.Finally aiming at getting the largest capacity,the method of selecting location of U-turn openings at the intersections with single left-turn lane is established.Thirdly,the location of U-turn openings at intersections with double left-turn lanes is researched.Based on the theory of traffic starting wave model,two expected transit time models respectively for the special left-turn lane and the left-turn and U-turn shared lane are established.Then combined the User-Optimized Equilibrium contained in Wardrop equilibrium theory,the comprehensive traffic capacity calculation model of double left-turn lanes is established.Finally aiming at getting the largest comprehensive capacity,the method of selecting location of U-turn openings at the intersections with double left-turn lanes is established.Finally,two examples are analyzed and verified by simulation.Two intersections with U-turn openings in Zibo city are selected,respectively as the instances setting single left-turn lane and double left-turn lanes to make surveys.With the calculation methods introduced in this paper,the optimal locations of U-turn openings at those intersections are found out.The results show that the methods can improve the traffic capacity of the shared lane from 432 to 509 pcu/h by 17.82%,and can improve the comprehensive traffic capacity of double left-turn lanes from 643 to 691 pcu/h by 6.95%.Then VISSIM simulation software is applied to establish the simulation models of two intersections,at last the simulation results are basically consistent with the results of model calculation.