Modeling For Traffic Overflow And Its Simulation On Urban Arterial Road

With the development of urbanization speeding up, car ownership of per urban person rises rapidly and causes unprecedented pressure to urban traffic network with extremely limited space. In recent years, although transportation engineering science and information technology have made obvious progress and brought great development prospects to the Intelligent Transportation System (ITS), traffic problems still can’t be solved and congestion is still the crucial ill of urban traffic and energy waste, environment pollution and safety incidents are consequent derivative problems.Traffic congestion is one of the hot issues for domestic and foreign traffic region researchers in recent years. To solve the traffic congestion problem, the key is to dig the generation mechanism of traffic congestion deeply, establish a scientific and reasonable mathematical model to portray the complex and changeable traffic generation process, and then select the targeted control strategies, to realizes the dynamic equilibrium between supply and demand of traffic. The key point to restrict traffic capacity of the arterials is intersection. The traffic capacity of an intersection is lower than a link because of the bottleneck effect and excessive traffic demand will lead to congestion. The traffic spillover is an extreme phenomenon of intersection traffic congestion and it will lead to four directions grid lock as the center of the original congestion intersection. With the increase of the grid lock intersection occurs, the entire road network will happen large scale congestion. Therefore, to explore a reasonable control method to avoid traffic spillover is very meaningful.Queue length is the key factor to traffic spillover and is the start point of the traffic spillover formation mechanism research. Based on the above basic ideas to solve the traffic congestion, this paper studies the dynamic process of queue growth and dissipation deeply, shockwave theory is used to analysis the queue process of a single intersection, and the traditional shockwave theory is improved, real-time queue length is obtained by the video detector, shockwave theory based on queue is proposed and the accuracy of queue length estimation based on shockwave theory is improved. The shockwave theory and cumulative input-output method are combined to analysis the queue process of a link, shockwave theory based on queue is used to estimate queue dissipate velocity, queue length of a link after sometime is estimated according to the cumulative principle, the shortcoming of stable traffic flow acquired of traditional traffic-wave theory is conquered and robustness of the model is increased. At last, traffic spillover formation mechanism is present according to above researches and spillover formation mechanism model based on physical queue is proposed. Estimate method of spillover duration time and average overflow queue length are also proposed. The simulation shows the basic idea of the method is relatively consistent with the actual traffic overflow status.Moreover, this paper also presents the spillover control model. A signal offset optimal ideology aimed to avoid spillover of arterials under coordinated control strategy is proposed based on previous single-point signal timing and coordinated control strategy researches. According to arrival vehicles from start time of a cycle to the maximal queue time of the downstream intersection add initial queue vehicles equals vehicles dissipates from the downstream, the threshold of offset is derived when a spillover is happening based on shockwaves theory and cumulative input-output method. Example analysis is implemented by change traffic flow and queue, offset thresholds are calculated respectively. Results shows the model can avoid traffic spillovers visibly.This paper presents a traffic spillover formation mechanism model and a traffic spillover control model, revealed the reasons for the formation and control methods of traffic grid lock congestion, provides a theoretical basis to solve the traffic grid lock congestion, riches the microscopic traffic flow theory and provide a new theoretical method for microscopic traffic flow theory and control strategies.