Leveraging cooperative connected automated vehicles for mixed traffic safety

The introduction of connected and automated vehicles (CAVs) is expected to reduce congestion, enhance safety, and improve traffic efficiency. Numerous research studies have focused on controlling pure CAV platoons in fully connected automated traffic, as well as single or multiple CAVs in mixed traffic with human-driven vehicles (HVs). While cruise control designs for CAVs have been proposed to stabilize car-following dynamics, few studies have addressed their impact on safety, particularly the trade-offs between stability and safety. In this paper, we study how cooperative control strategies for CAVs can be designed to enhance the safety and stability of mixed traffic, under various levels of connectivity and automation. Considering mixed traffic where a pair of CAVs travels amongst HVs, we design cruise control strategies for the head and the tail CAVs to stabilize traffic via cooperation and, possibly, by also leveraging connectivity with HVs in-between. We introduce the definition of CAV safety, HV safety, and platoon safety, and investigate the real-time safety impact of the CAV controllers using control barrier functions (CBFs). Safety-critical control strategies are then derived by incorporating CBF safety constraints for online computation. Both theoretical and extensive numerical analysis have been conducted to explore the effect of CAV cooperation and HV connectivity on the stability and safety of mixed traffic. The cooperative strategy for CAV control improves stability, and potential safety issues are successfully resolved with the proposed safety-critical design. Moreover, connecting CAVs with the HVs between them offers additional benefits: if HVs are connected to the tail CAV, traffic stability is further improved compared to when they are connected only to the head CAV; whereas if HVs are connected to the head CAV, their safety can be enhanced.