On the Urban Link Fundamental Diagram Based on Velocity-Weighted Flow and Queue Length

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.

Improving the performance of unsignalized t-intersections within CAVs mixed traffic

“…Due to the stochastic nature of traffic arrivals, a minimum of 10 simulation runs were performed with different random seed numbers to ensure that the values reported incorporating the stochastic changes in traffic flow. Since the car-following behavior has a direct impact on creating gaps by reducing speed and traffic flow, the Wiedemann 99 model has been chosen in this work because it is more advanced and flexible than Wiedemann 74 [40]. the Wiedemann 74 is recommended by the VISSIM user manual to be used in urban areas where Wiedemann 99 can be used on freeways and multilane highways [41].…”