Study On Capacity And Signal Control Methods Of Roundabout

The roundabouts that appear in19th century have many advantages, related tofacilitating management, less conflict points, safe driving and more continuous flows.Especially when traffic volume is low, the headway will obey negative exponentialdistribution or shift negative exponential distribution and the traffic is in a state of free flow.The roundabout is rather economic and efficient in term of traffic organization forintersections because of higher capacity than common cross-intersection; therefore it playsan important role in the development of urban transport. However, with the sustained andrapid development of China’s economy and society, traffic demand increase concurrently inurban road, which results in exposure of weakness of the roundabouts without signal control.In reality, the roundabouts, as urban transport important node, often lock and have too longentrance queue as the traffic volume increases rapidly. To take full advantage of roundaboutsto achieve the purpose of improving the entire road network capacity in spatial and temporal,one effective method is signal control matching with real-time traffic condition according toreal circumstance in roundabout, the signal control and roundabouts geometric featuresorganically combined. In the peak-hour of traffic, this method can eliminate the conflict andcongestion problems existed in roundabouts by signal control. At the same time, it retains theroundabouts’ advantages of optimization for traffic condition in flat peak-hour of traffic andadaptability in good traffic condition.Firstly, this thesis describes research background, analysis literature review at home andabroad about roundabouts and overviews current researches from the overall perspective.Then significance and purpose of this thesis are determined and thus the main content andoverall technical route are established.Secondly, several comparatively common calculation method of roundabouts capacityis summarized. And calculation method of design capacity is derived based on the capacityof weaving section, thus deduces the conditions of control methods about roundabout.Thirdly, this thesis introduces some calculation methods of signal cycle that are usedmore commonly at present. Due to the particularity of roundabouts, the existing signalcontrol methods can’t have a better adaptation, thus ALINEA algorithm is introduced intoroundabouts for traffic signal coordination control based on the capacity-demandrelationship in ring road. Then dynamic calculation methods of signal cycle are discussed.Finally, the survey by analyzing traffic situation on Xinmin Square shows that thepeak-hour traffic volume is greater than the design capacity of roundabout without signalcontrol. This thesis replans Xinmin Square by re-canalization and signal timing, then import the signal group into the VISSIM program for simulation. The result shows that if the signalcontrol is suitable, the method not only can greatly increase the capacity of roundabouts, butcan accommodate the increasing traffic demand to a certain extent in the future.