Connected and Autonomous Vehicle Platoons and Traffic Bottlenecks: Effects on Recurrent and Non-Recurrent Congestion in Mixed Traffic Conditions

Connected and autonomous vehicles (CAVs) are expected to play a transformative role in highway traffic, particularly through platooning strategies. Specifically, they are expected to enhance operational conditions at bottlenecks by reducing the propagation of congestion and the emergence of safety-critical conflicts. In these contexts, CAV platoons might increase flow capacity by operating with shorter headways, while they could enhance safety by adopting more coordinated maneuvers. While existing research has shown the potential of CAVs to enhance traffic performance, significant gaps remain regarding how platoons behave under bottleneck conditions, especially in mixed traffic with both CAVs and human-driven vehicles (HDVs). This chapter explores the impacts of CAV platoons on highway traffic performance under mixed traffic conditions, focusing on their role at bottlenecks. Two cases are considered: (i) a recurrent bottleneck in a highway merging area, where the interaction between entering and mainline flows typically generates congestion, and (ii) a non-recurrent bottleneck produced by a vehicle breakdown, causing temporary capacity reduction. Using microsimulation-based analyses, this study investigates how platoon size and CAV market penetration rate (MPR) influence traffic capacity, travel times, and environmental impacts. Results show that CAV platoons may reduce congestion in recurrent situations and improve resilience under non-recurrent disruptions: specifically, in highway merging areas, platooning increases flow capacity and reduces travel times, while in the case of vehicle breakdowns, platoons help mitigate capacity drops and limit delays, particularly at higher MPRs and moderate platoon sizes. These findings contribute to a deeper understanding of the opportunities and challenges of CAV platoon deployment.