Research On The Signal Warrant For Roundabouts

At present, roundabouts are mostly non-signal control in our country, relying on vehicles’ self-organized to operate. The biggest drawback of non-signal control roundabout is that when the traffic volume becomes large, the capacity of self-organizing roundabout gets low, the conflicts between vehicles become large and chaos. These will cause a reduced capacity, a lower operating efficiency, and the inner ring of roundabout "lock" phenomenon more seriously. Vehicles at the exit are blocked and hard to exit while the vehicles at the entrance are difficult to enter. Thus, roundabout can deal with the traffic congestion which caused by increasing traffic flow. There will be some advantages if the roundabout is controlled by signal: a. The improvement of traffic order of the intersection. When the flow of non-signal control roundabout approach or exceed the capacity of the intersection, the traffic will be blocked and congested. But if the signal control is taken, the conflicts between the vehicles will be separated from both time and space. b. Improve the capacity of roundabouts. Vehicles of roundabouts intertwined freely on the ring road, the interleaving behavior limits the capacity. If taken signal control, the weaving section will be shorten, and interleaving behavior will be reduced, too. Thereby the average delay will be reduced. 3. Improve the safety of mixed traffic flow. After taking signal control, the conflicts between vehicles, non-motor vehicles and pedestrian is eliminated, which will ensure the traffic flow of intersections conduct orderly. Besides, it will ensure the safety of pedestrians and non-motor vehicles. However, when traffic flow is low at the intersection, the stopping-delay of vehicles will increase the average delay. Therefore, it’s necessary for the roundabout to set a reasonable warrant to decide whether or not taking signal controlOn the basis of the sum up the research results, this paper uses theoretical modeling and simulation analysis as the main means, combining Changchun’s actual intersection to verify, proposed a signal warrant for roundabouts. The main parameters are the capacity and average delay time. This paper improved the current capacity model and the delay model based on distribution theory and gap acceptance theory to make it adapt to the signal control roundabouts’ operating rules. Mainly completed work and conclusions are summarized as follows:(1)vehicle headway distribution analysis of roundaboutsThis paper investigated of the actual distribution of roundabout, organized and substituted into the theoretic model to verification, finally get the headway distribution which comply with the actual situation.(2)building the capacity model of signal control roundaboutsBased on gap acceptance theory and the headway distribution, signal timing, geometry of the roundabout, this paper built a capacity model, tested and verified the model using the actual roundabout’s data. It also analysis the influence of different parameters on the capacity, such as follow-time and the signal cycle, and the conclusion is consistent with the actual situation.(3)signal warrant for roundaboutsBasedon non-signal control and signal control roundabout’s average delay under the same conditions, this paper finds the critical flow when the delay is same. When traffic flow rate is less than the critical flow rate, signal control is not necessary to take, but when the flow exceeds the critical flow, signal control should be taken to ensure the efficiency of the intersection.In this paper, the capacity,the average delay and the signal warrant of roundabouts under signal control is discussed deeply. But with the limit of date and vigor, the research has some limitations, so the paper concludes with prospects and future research plans at the end of the paper.