Study On Principles Of Operation On Protected Left-turn Phase At Signalized Intersection

Title: Study on Principles of Operation on Protected Left-turn Phase at SignalizedIntersectionMajor: Traffic Information Engineering & ControlAdviser:Prof. Wang DianhaiThe left-turn flow is the flow that has the most conflict at the signalizedintersection. So it's an important question in the study on signalized control thathow to control the left-turn flow. The control methods of the left-turn flow ismainly operating the protected left-turn phase. Because it can avoid the conflict ofthe left-turn flow and the opposing straight flow on the time, and then improve thesecurity degree of the signalized intersection.The lack of the specific principles of operation on protected left-turn phasealways results in the following two irrational instances at the signalized intersection.Firstly, There is no protected left-turn phase at the intersection when the flow islower, resulting in a directional flow is zero, however, another directional flow isqueuing. Secondly, There is protected left-turn phase at the intersection when theflow is greater, leading to the reduced intersection's capacity and the increaseddelay of the vehicles because the conflicts between the left-turn flow and theopposing straight flow become more serious. The main reason of that contributes tothe above instances is that lack of the specific principles of operation on protectedleft-turn phase on the design for the traffic signal. For the sake of providingspecific principles for signal timing design, this paper focuses on the capacity ofleft-turn vehicles, the Conflict delay of the left-turn flow and the straight flow atthe typical two-phase intersections, in combination with the researches on theprinciples of operation on protected left-turn phase based on the Key Project ofNational Natural Science Foundation "Research on the principal theoretical modeland simulation technique of dynamic traffic management and control in urbannetwork", the Project of National Natural Science Foundation "Research onConflict Mechanism and Essential Parameters in Mixed Traffic", the joint researchproject for Hisensoft Network Science Co. Ltd "Research on the theory, algorithmand simulation of self-adapted control technique theory and simulation technical inmixed traffic situation".This paper analysed the conflict mechanism of the left-turn flow, the opposingstraight flow and the defects in the traditional methods. A new model is developedfor left-turning crossing the opposite through vehicles with limited priorityaccording to the traditional model of gap acceptance. Then a model for calculatingthe left-turn vehicles' capacity is built. By applying field data, the model provesfeasible in practice to compute the capacity of left-turn vehicles for typicaltwo-phase intersections.According to the running characteristic of the left-turn flow and the opposingstraight flow, the delay is divided into two parts: the control delay and the conflictdelay. This paper focuses on the conflict delay of the left-turn flow and the straightflow. Firstly, A new model is developed for calculating the conflict delay of theleft-turn flow based on the traditional delay model about unsignalized intersection.Then another model is developed for calculating the conflict delay of the straightflow by making use of the queueing theory and the probability theory.The average delay is one of the most important variables that reflects theperformance of traffic operations at an intersection. The rule of signalized control isthat the least delay and queue lengths with the enough capacity. Based on the abovedelay models, this paper deduced the average delay of all vehicles at anintersection in the situation of before and after operating the protected left-turnPhase. Then, the minimum of the left-turn flow for operating the protectedleft-turn phase when the straight flow is fixed, is the principles of operation onprotected left-turn phase.The models that were provided in this paper have been tested by field data,and prove feasible in practice. The results have the reference and application valuefor the traffic control.