Research On Speed-Flow Relationships Of The Urban Roads In Beijing

With the rapid increase of vehicles, the improvement of transport systemconstruction, as well as the application of ITS of Beijing, traffic system operatingenvironment had changed significantly. As a result, systematic studyof traffic flow isnecessary. Studyonspeed-flowrelationshipis thebasicoftraffic flowcharacteristics.It's thebasic elementto detemine capacityofroadway,andis the necessaryconditionto measure level of service. It has a wide range of applications in traffic planning,road construction, traffic management and control. Therefore, there is enormoustheoretical and practical significance to do a systematic research on speed-flowrelationshipsoftheurban artrrialsinBeijing.This paper is based on the collaborative research projects of Beijing Universityof technology and Beijing Urban Planning and Design Institute. The name of theproject is "Study of Capacity and Planning Parameter Calibration of Beijing'sRoadingNetwork".Using video camera method, traffic data of major/minor roads is collected andprocessed by Autoscpoe2004. The traffic flow at basic sections of the urban arterialhasdiscontinuouscharacteristics.Andtrafficflowstatisticsintervalisdetermined.Based on the classic speed-flow model andusing subdivided-modeling methods,Greenshields speed-flow model is established. Based on the survy data, it can befound that this model does not conform to the realityof the situation. So the modifiedGreenshields speed-flow model is established. Greenshields-LN model and LN-Linemodel are established by analyzing congested and free traffic flow operationconditions mechanism. Based on the comparative analysis of capacity, minimumspeed, the speed of maxmum flow and maxmum speed, Greenshields—LN model isconsidered as the best one to describe the Speed-flowrelationship of the urban roadsinBeijing.Finally,maininfluencingfactorsofthemodel are analyzed.Theinfluence ofbusstops is discussed.The impact of speed-flow model of the distance from theintersectionisstudied byanalyzingthesurveydataandsimulationdata.