Safe and Efficient CAV Lane Changing using Decentralised Safety Shields

--Lane changing is a complex decision-making problem for Connected and Autonomous V ehicles (CA Vs) as it requires balancing traffic efficiency with safety. Although traffic efficiency can be improved by using vehicular communication for training lane change controllers using Multi-Agent Reinforcement Learning (MARL), ensuring safety is difficult. T o address this issue, we propose a decentralised Hybrid Safety Shield (HSS) that combines optimisation and a rule-based approach to guarantee safety. Our method applies control barrier functions to constrain longitudinal and lateral control inputs of a CA V to ensure safe manoeuvres. Additionally, we present an architecture to integrate HSS with MARL, called MARL-HSS, to improve traffic efficiency while ensuring safety. We evaluate MARL-HSS using a gym-like environment that simulates an on-ramp merging scenario with two levels of traffic densities, such as light and moderate densities. The results show that HSS provides a safety guarantee by strictly enforcing a dynamic safety constraint defined on a time headway, even in moderate traffic density that offers challenging lane change scenarios. Moreover, the proposed method learns stable policies compared to the baseline, a state-of-the-art MARL lane change controller without a safety shield. Further policy evaluation shows that our method achieves a balance between safety and traffic efficiency with zero crashes and comparable average speeds in light and moderate traffic densities. I NTRODUCTION Autonomous V ehicles (A Vs) were expected to be commercially available by 2020, but recent reports suggest that wider adoption of A Vs can only be expected after 2030 or beyond due to societal, regulatory, and technical challenges [1]. Complex technical problems, such as localisation, mapping, perception, route planning, and motion control, are yet to be solved to enable commercial A V deployments [2].