The Study Of Two-lane Roundabout Traffic Flow Characteristics Based On Cellular Automaton

With the social economics development, the conflict between the traffic demand growth and the relative backwardness of transportation construction has become more and more serious. The traffic congestion problem and traffic accidents such as vehicle rear-end collision have caused many troubles in the process of urban traffic development, and it makes domestic and foreign experts put forward many traffic models helping alleviating traffic congestion and reducing traffic accidents. Among the traffic-flow models, the Cellular Automata (referred to as CA) model is well known for its simplicity, finiteness and easy to realize on the computer. CA can simulation many kinds of complex natural and physic phenomena just with some simple rules, and the simulation results are good. Also it is applied in simulating traffic problems.The foreign study on the roundabout traffic flow only considers two perpendicular lanes and the vehicles on the lanes just going straight not turning. Its simulation result shows that the delay time is influenced by the roundabout size. Based on the domestic and foreign roundabout traffic flow study, assuming that the vehicles enter and leave the roundabout from four different directions, the roundabout traffic behavior characteristics are analyzed through CA simulation. First the single-lane roundabout simulation results shows that the roundabout size, the driver attribute, the roundabout limit speed and the turn probability have few influences on the total delay time. But these results seems to be different form the actual roundabout traffic flow characteristics in intuition, the reason is that there is no the vehicle lane changing behavior in the single-lane roundabout which cause the above parameters have nothing to do with the total delay time. So it is necessary to analyze the double-lane roundabout traffic flow behavior. By finding vehicle's anticipant driving line in roundabout on condition that the flow is unlimited, the critical space and limit positions are got when the vehicles change its lane in the double-lane roundabout. Further, on condition that the flow is unlimited, the vehicle lane changing rule is described, and based on this, a CA model of double-lane roundabout is established, and through numerical simulation, the traffic flow typical characteristics are got, it shows that the roundabout size, the driver attribute, the roundabout limit speed and the turn probability influences the total delay time because of the vehicle lane changing behavior. Because of there is a certain limitation in using single-lane roundabout to simulate roundabout traffic flow characteristics. It is necessary to obtain the traffic flow characteristics through double-lane roundabout simulation. Of course, the above research achievements can be applied in planning and designing the roundabout organization.