Abstract
For uninterrupted traffic flow, it is well-known that the fundamental diagram (FD) describes the relationship between traffic flow and density under steady state. To study the characteristics of interrupted traffic flow on a signalized link, a link fundamental diagram (LFD) for urban roads is proposed in this paper. First, a new variable, which synthesizes traffic flow with the speed of each vehicle, is defined. Then, the link fundamental diagram is obtained by drawing a scatter-plot of the velocity-weighted flow versus queue length, which takes on a unimodal curve with an approximately symmetric shape. Finally, simulation studies are conducted by modeling an urban link based on the traffic simulation software VISSIM. Compared with the traditional fundamental diagram, the proposed link fundamental diagram is more intuitive for showing the relationship between traffic condition and queue length. The impacts of the cycle time, green time, and split on the proposed link fundamental diagram are studied. Simulation results show that the shape of the link fundamental diagram fundamentally is determined by the split. The critical point is correlated to split values, and the green time exerts a great influence on both the velocity-weighted flow and the critical queue length. The cycle time has little effect on the critical queue length but has a great influence on the velocity-weighted flow.
Highlights
Fundamental diagrams (FDs) show the speed-density or flow–density relationship, which has been considered as the foundation of traffic flow theory
A new kind of link fundamental diagram (LFD) based on the velocity-weighted flow and queue length is presented in this paper, which can show the relationship between traffic condition and queue length
We have studied the link fundamental diagram under a condition where the cycle time is fixed with different green times
Summary
Fundamental diagrams (FDs) show the speed-density or flow–density relationship, which has been considered as the foundation of traffic flow theory. A non-equilibrium traffic model considering the vehicle velocity was presented, which is hyperbolic and has two characteristic fields, and it is shown to exhibit correct queue-end behavior and can explain some of the observed traffic phenomena that challenge old models [11] To date, FDs have been used for traffic state evaluation, ramp control, variable speed limit control, highway capacity analysis, and level of service [12] Most of these studies on FDs have focused on uninterrupted traffic flows (e.g., freeway traffic flow), there is limited related research on interrupted traffic flows (e.g., an isolated signalized intersection, a signalized coordinated link, a network with signalized intersections). A new kind of link fundamental diagram (LFD) based on the velocity-weighted flow and queue length is presented in this paper, which can show the relationship between traffic condition and queue length.
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