Rhythmic Control of Automated Traffic—Part II: Grid Network Rhythm and Online Routing

Connected and automated vehicle (CAV) technology is providing urban transportation managers tremendous opportunities for better operation of urban mobility systems. However, there are significant challenges in real-time implementation as the computational time of the corresponding operations optimization model increases exponentially with increasing vehicle numbers. Following the companion paper (Chen et al. 2021), which proposes a novel automated traffic control scheme for isolated intersections, this study proposes a network-level, real-time traffic control framework for CAVs on grid networks. The proposed framework integrates a rhythmic control method with an online routing algorithm to realize collision-free control of all CAVs on a network and achieve superior performance in average vehicle delay, network traffic throughput, and computational scalability. Specifically, we construct a preset network rhythm that all CAVs can follow to move on the network and avoid collisions at all intersections. Based on the network rhythm, we then formulate online routing for the CAVs as a mixed integer linear program, which optimizes the entry times of CAVs at all entrances of the network and their time–space routings in real time. We provide a sufficient condition that the linear programming relaxation of the online routing model yields an optimal integer solution. Extensive numerical tests are conducted to show the performance of the proposed operations management framework under various scenarios. It is illustrated that the framework is capable of achieving negligible delays and increased network throughput. Furthermore, the computational time results are also promising. The CPU time for solving a collision-free control optimization problem with 2,000 vehicles is only 0.3 second on an ordinary personal computer.

WDM Long-Haul Networks

Ever-increasing traffic in the long-haul networks called for WDM-based transmission, all the more when compared to the metro and access segments. Further, although the interconnected WDM rings served the needs of long-haul networks for some time, mesh-connected WDM networks appeared as a natural and more effective solution, with enhanced connectivity and resilience against network failures. In this chapter, we first examine the basic design challenges and the candidate node configurations for WRON-based mesh networks. Next we present various offline design methodologies for this class of networks using LP-based and heuristic schemes. Impact of wavelength conversion (WC) in mesh-configured WRONs is also examined by using analytical models, and the gain in bandwidth utilization is assessed in WRONs with full WC as compared to those without any WC. Finally, we examine some online routing and wavelength assignment schemes that can be used for operational WRONs. (143 words)