Network traffic instability in a two-ring system with automated driving and cooperative merging
For traffic engineers and researchers, it reveals that cooperative merging is crucial for network stability when AVs are widely deployed, while non-cooperative AVs can degrade performance.
This paper models network traffic instability in a two-ring system with automated and connected vehicles, finding that cooperative merging improves stability but non-cooperative AVs worsen instability at high turning probabilities, causing NFD bifurcation before critical density.
In this paper, we characterize the effects of turning and merging maneuvers of connected and/or automated vehicles (CAVs or AVs) on network traffic instability using the macroscopic or network fundamental diagram (MFD or NFD). We revisit the two-ring system from a theoretical perspective and develop an integrated modeling framework consisting of different microscopic traffic models of human-driven vehicles (HVs), AVs, and CAVs. Results suggest that network traffic instability due to turning and merging maneuvers is an intrinsic property of road networks. When the turning probability is low, CAVs do not significantly change the NFD bifurcation, but scatter in both the simulated link fundamental diagrams (FDs) and NFDs reduces leading to higher and more stable network flows. When the turning probability is high, non-cooperative AVs worsen network traffic instability - the NFD undergoes bifurcation long before the critical density is reached. Results highlight the important impact of cooperative merging on network traffic stability when AVs are widely deployed in road networks.