Cooperative Automated Emergency Braking for CAVs under Time-Varying Communication Delays

Connected and Automated Vehicles (CAVs) have the potential to significantly improve road safety, fuel efficiency, and traffic flow by forming platoons with short inter-vehicle gaps, enabled by vehicle-to-vehicle communications and onboard sensors. However, wireless connectivity for CAVs is subject to time-varying delays, which can significantly impact platoon safety during emergency braking. To this end, this paper evaluates the communication delays incurred by platoon vehicles during emergency braking under various data and traffic densities. Additionally, an emergency braking strategy named adaptive emergency braking is proposed and compared with five other strategies based on their ability to meet the functional requirements of collision avoidance and minimizing the stopping distance of the platoon lead vehicle, which are crucial for transitioning a platoon to a fail-safe state. Moreover, the emergency braking strategies are evaluated through rigorous simulations, considering non-functional criteria such as required inter-vehicle gaps, maximum allowable deceleration rates, and their robustness under time-varying communication delays.

I. Introduction

Platooning is a promising application of Connected and Automated Vehicles (CAVs) that has garnered significant attention from the automotive industry and traffic authorities worldwide [1]. In platooning, a Lead Vehicle (LV) leads a group of Following Vehicles (FVs), which rely on Vehicle-to-Vehicle (V2V) communications and sensors to track the LV's movements in both the lateral and longitudinal directions. The LV periodically transmits time-triggered messages containing essential data, including its position, speed, acceleration, and steering angle, to enable the FVs to maintain autonomous control. In case of an emergency, the LV can send out event-driven messages to trigger, e.g., emergency braking, specifying the hazard's type and severity, when and how to brake, and the necessary deceleration rate to avoid the hazard. These event-driven messages must be delivered with high reliability to all vehicles in the area of interest and, therefore, are repeated periodically at a certain frequency for the duration of the event. Frequency (Hz) can be defined as the number of times time-triggered or event-driven messages are transmitted per second.