Urban Elevated Expressway Traffic Congestion Analysis And Control Based On VISSIM Traffic Simulation

Along with the growth of China’s economic strength and the surge in the number of motor vehicles, urban traffic has developed gradually from plane transportation to three-dimensional transportation. In order to ease the traffic pressure, many cities have constructed elevated expressway. But, with the continued growth of motor vehicles, the traffic flow of elevated expressway exceeds the load, which leads to urban elevated road congestion, especially intermittent elevated expressway. Therefore, it is necessary to solve the congestion of elevated expressway. This research mainly does the following work.Firstly, this paper does some theoretical research in the elevated congestion reasons and control methods. It mainly analyses the characteristics of traffic flow and ramps and weaving area in the first place, and this paper introduces the density to the service level evaluation, which lays the theoretical foundation for the cause of traffic congestion in the simulation experiment. Then, according to the characteristics of the elevated expressway congestion, this paper introduces some relevant solution strategy and control methods and mainly studies the main parameters and the process of the induction control.Secondly, this paper analyzes the reasons of viaduct congestion by traffic simulation. It selects Tumen’s elevated expressway as the research object, which is intermittent near the West Second Ring Road in Xi’an. The weaving area is more complicated. According to analysis of actual survey data, the parameters of the VISSIM software is demarcated, and then simulation model is established. The simulation experiment result shows that the maximum length of the queue on the exit ramp is less than the length of the ramp and the exit ramp queuing vehicles will not overflow to the elevated and interfere with the traffic. The reason of the congestion will to be summarized according to the simulation results. Flat peak moment, weaving area appears accidental congestion because of the traffic demand of the entrance ramp accidentally increasing. Rush moment, the elevated road traffic paralysis, the main reason is that elevated expressway traffic flow is saturated and traffic inflow reaches 1545veh/h, which will seriously interfere with the traffic on the elevated expressway. And its continuous flow into the elevated expressway will make it paralyze.Finally, in view of different reasons of the congestion in the flat peak hour and rush hour, this paper makes the different measures. And the measures should be verified in the simulation experiment. As the queuing vehicles will not overflow to the elevated expressway in the exit ramp, so it will not interfere with traffic in the elevated expressway. Therefore, there is no need to control by induction at the junction of the exit ramp and ground road, and it is only need to control the entrance ramp. It takes the entrance ramp control of induction in peak time, which uses ALINEA algorithm. And the program is written in the simulation software by the VisVAP. The strategy is forbidding the ground traffic vehicles to enter the elevated in rush hour. The simulation results by VISSIM show that: to take the entrance ramp control method to accidental congestion mitigation effect is obvious in flat peak moment; to take the entrance ramp provisional close control method to crippling congestion is remarkable in rush hour.