# Coordinated Multi-Platooning Planning for Resolving Sudden Congestion on Multi-Lane Freeways
## 1 Introduction  
Resolving bottlenecks on the freeways has been a challenge in modern society [1]. The goal is to quickly release the vehicles stuck in a congested area, maintain the safety for the approaching vehicles to pass through, and further improve the road usage efficiency. There are two approaches used to solve this congestion problem. The first one is to let vehicles voluntarily line up to drive through the congestion area. However, when many vehicles are stuck in chaos in the congestion area, drivers tend to adopt the \"me-first\" exit strategy, which often leads to the further deterioration of traffic. For example, the unpredictable behavior of an aggressive driver, who attempts to exit the blockage point arbitrarily, can worsen the congestion. Consequently, the vehicles may have a long wait before being able to leave the congestion area. In the second approach, the vehicles on the freeways must communicate with each other, e.g., through Dedicated Short-Range Communication (DSRC), to build a consensus movement plan. In the literature, there are several existing studies that adopt this approach [2; 3; 4; 5]. For example, [PERSON] et al. [2] summarized the methods for the coordination of connected and automated vehicles at the intersections and merging at highway on-ramps. The idea of forming platoons to improve traffic flow was first introduced in this study. The authors in [6] presented a method to reserve virtual slots,and the drivers pay the fee depending on their traveling needs. Generally, these models aim to coordinate traffic in intersections or known crowded areas. Cooperative Adaptive Cruise Control (CACC) is one of the promising protocols used to resolve potential conflicts [3,4]. However, the configuration for the protocol must be pre-defined. In the temporary traffic bottleneck cases, the vehicles must be grouped first before the control can be activated. This is because the vehicles are already in chaotic order and should be sorted before CACC can run smoothly. In addition, releasing congested traffic and handling approaching vehicles must be controlled simultaneously to avoid a worse situation, such as tailgating. The congestion resolution's key point is finding an optimal plan for individual vehicles to exit the accident spot reasonably. In this case, maintaining two goals (traffic congestion resolution and vehicle safety movement) for reducing localized traffic disruptions is a critical issue but is yet to be well-explored. Recently, the 3 rd Generation Partnership Project (3 GPP) has proposed technical specifications for Vehicle-to-Everything (V2X) [7], particularly in the Fifth Generation (5G) networks [8], to enhance communications for connected vehicles. However, vehicle merging and lane-changing are among the dangerous maneuvers which are often complicated to control without proper coordination [9]. To address the challenge, we further explored previously published literature [10] to build a novel decentralized Coordinated Platooning Planning (CPP) method. In this model, the vehicles automatically exchange messages (via vehicle-to-vehicle communications) to form platoons and cooperate to move in order without communicating with core network infrastructure (e.g., a centralized server). In contrast to the decentralized model, the centralized model usually requires a central system to collect a large amount of information and high-performance hardware to assist platoon forming and vehicle control. Our decentralized approach is highly suitable for traffic coordination on highways in which cellular networks are not always reachable. In particular, inspired by the recent development of 5G Vehicle-to-Vehicle (V2V) communications [11], our method aims to maintain multiple goals (e.g., road capacity improvements, collision prevention, lane-changing coordination, and waiting for time reduction for the vehicles to exit the bottleneck spot) for alleviating traffic jams caused by lane closure or accident events on the freeways.