Assessing the safety benefits of CACC+ based coordination of connected and autonomous vehicle platoons in emergency braking scenarios

TL;DR

The paper tackles the safety assessment of cooperative adaptive cruise control in vehicle platoons under emergency braking, comparing CACC (information from one predecessor) with CACC+ (information from multiple predecessors) within a constant time headway scheme and standstill spacing. It develops a vehicle-string model with uncertain actuation lag and a decentralized r-look-ahead controller, and then discretizes the dynamics using RK4 while evaluating safety via Monte Carlo simulations that estimate collision probability $\mathbb{P}$, expected collisions $\mathbb{N}$, and collision severity $\mathbb{S}$. A collision model is paired with a Monte Carlo safety evaluation pipeline, incorporating actuator saturation and random deceleration $D_i$ to reflect real-world variability. The results indicate that CACC+ generally reduces $\mathbb{P}$ and $\mathbb{N}$, and can match or exceed CACC safety performance at smaller standstill spacings, highlighting the practical value of information-sharing topologies for safe platooning in emergencies.

Abstract

Ensuring safety is the most important factor in connected and autonomous vehicles, especially in emergency braking situations. As such, assessing the safety benefits of one information topology over other is a necessary step towards evaluating and ensuring safety. In this paper, we compare the safety benefits of a cooperative adaptive cruise control which utilizes information from one predecessor vehicle (CACC) with the one that utilizes information from multiple predecessors (CACC+) for the maintenance of spacing under an emergency braking scenario. A constant time headway policy is employed for maintenance of spacing (that includes a desired standstill spacing distance and a velocity dependent spacing distance) between the vehicles in the platoon. The considered emergency braking scenario consists of braking of the leader vehicle of the platoon at its maximum deceleration and that of the following vehicles to maintain the spacing as per CACC or CACC+. By focusing on the standstill spacing distance and utilizing Monte Carlo simulations, we assess the safety benefits of CACC+ over CACC by utilizing the following safety metrics: (1) probability of collision, (2) expected number of collisions, and (3) severity of collision (defined as the relative velocity of the two vehicles at impact). We present and provide discussion of these results.

Figures (15)

• Figure 1: An illustration of the connected and autonomous vehicle platoon with V2V communication.
• Figure 2: An illustration of the saturation function $sat(u_i)$.
• Figure 3: The probability distribution of the maximum deceleration godbole1997tools.
• Figure 4: The admissible regions of $k_v$ and $k_p$.
• Figure 5: The probability of collision when $d = 2$ m.