Traffic Operation Characteristics Of Roundabout

The present paper which is mainly depends on the State Natural Sciences Foundation key project "Research on essential theory and the technique of simulation for the urban road network dynamic traffic control" and Liaoning Province education department project "Study of roundabout capability and the transportation organization ", has conducted the deep research to the traffic flow operating characteristic on the roundabout.The roundabout which sets a big radius island at the central of plane intersection, makes all the direct, left vehicles moving counterclockwise around the central island and also makes the conflict spot becoming weaving spot in its travel process, thus guarantes traffic safety of the road intersection at the result of improving capability of the road intersection. Actual investigation and analysis on operating characteristic has important significance to the theory and practice, and also provide important theoretical basis for the roundabout capability, the delay and the service level analysis, the road intersection channelized layout, the transportation organization and so on. This paper has analysed the basic characteristic and rule of roundabout traffic flow movement, has proposed the related analysis's method and also has provided the basis to establish the roundabout analysis, organization, design method to suit our country transportation environment by long-term traffic survey on Dalian ten roundabouts. The paper is mainly constituted by following three parts:1) The roundabout geometry characteristic and the vehicles movement behavior The geometry characteristic is inherent attribute of the roundabout and decides the roundabout vehicles' movement behavior directly. This part first has summarized roundabout's related geometry characteristic, calssified the roundabout type, made the detailed division to the roundabout crossing region, and thoroughly analysed various regions vehicles operating characteristic. Based on this, lanechange rate as the main object, The paper studied the behavior characteristic of roundabout vehicles, researched the relations with parameter such as the traffic volume, the leg number, and weaving area length. It has established the quota relational model through the measured data to lay the foundation for traffic flow characteristic's following research.2) The roundabout traffic flow characteristic parameter The massive operation data on roundabout of Dalian urban district has been accumulated through the multi-criteria and long time field investigation. Through analysing the arriving, depart rule of leg vehicles and arriving characteristic of interweaves area vehicles, the paper established arriving distribution model. The paper has analyzed diffient space position's flow fluctuation characteristic of the roundabout from the macroscopic angle, and has also studied the influence on the entry volume of the radius of turn, the entrance traffic lane width, the entrance traffic lane number, interweave area length, central island radius, outer ring radius, circling traffic flow parameters and so on from the microcosmic angle,as well as estabilished the linear regression model. Through the quantity's cluster analysis on the roundabout speed characteristic data under the different space and time criterion, the paper has obtained the conclusion that the vehicle speed distribution at the same position traffic lane of the different roundabout tends the consistent. Then through the applying nuclear density estimate law to established velocity distribution model, the paper has got the velocity distribution characteristic.Through the nuclear density velocity distribution model, the paper has carried on the comparative analysis to each roundabout vehicle speed distributionn at the different lane, has carried on the qualitative analysis on influence from the different positon,the leg number, the geometric measurements,as well as has confirmed the above conclusion from the quota angle through the application variance analysis method to the vehicle speed. Through analyzing the traffic data of the crowed and unimpeded condition, the paper has proposed the application compound distribution model to descript roundabout complex headway distribution. Supposed headway distribution obedience negative exponent distribution under the free state, obedience logormal distribution under the crowded condition, the paper has established headway distribution model and estamited the parameter value appling the EM algorithm determination model. Through the contrast with the index distribution, Erlang distributes and the M3 distribution model, the paper has indicated that compound distribution's fitting precision is higher than other distribution models in view of the complex measured data.3) The roundabout operating efficiency According to mutual influence between different host road stream of vehicles, using three pattern separately which are one traffic lane pattern, the superimposition two-lane pattern and the synchronized two-lane pattern on processing,and has established invalid data rejection rule under the synchronized multiple track pattern. The paper proposed the multiple lane critical gap estimated method under three kind of patterns, based on the maximum likelihood estimated method. Through the analysis on the microscopic choice characteristic of leg vehicles pilot crossing the main road stream of vehicles, the paper took the risk function of time and the waiting time function as the foundation, proposed functional relations model about the critical gap and volume of the main road stream.This model which had thoeretically considered the main road stream running status' influence on the main road stream of vehicles critical gap's, can better tally with the actual situation. Taking Dalian's actual observation data as the foundation, the paper analyzied the statistical regression model between critical gap and the standby period curve.Based on this, the paper proposed the generall capability model with analysis on rounabout operating efficiency influencing factor', and has carried on the demarcation to the model related parameter. Taking the queue theory as the link, the paper inferred relational model between the delay and the traveling capability, and confirmed the model's high precision by using Wusi squares and Longquan square's actual data.In the end, the paper summaried the done work, analyzed the progress and the achievement obtained, and brong forward issues for further study.