A Cyber-physical Approach for Emergency Braking in Close-Distance Driving Arrangements

Abstract

In addition to fuel/energy savings, close-distance driving or platooning allows compacting vehicle flows and, hence, increasing throughput on congested roads. The shorter the inter-vehicle separation is in such settings, the more the benefits. However, it becomes considerably harder to guarantee safety, in particular, when braking in an emergency. In this paper, we are concerned with this problem and propose a cyber-physical approach that considerably reduces the stopping distance of a platoon with inter-vehicle separations shorter than one vehicle length (i.e., 5 m ) without sacrificing safety and independent of the road profile, i.e., whether on a flat road or in a downhill. The basic idea is to implement a cooperative behavior where a vehicle sends a distress message, if it fails to achieve an assigned deceleration when braking in a platoon. This way, other vehicles in the arrangement can adapt their decelerations to avoid collisions. We illustrate and evaluate our approach based on detailed simulations involving high-fidelity vehicle models.

Characterization of Transient Communication Outages Into States to Enable Autonomous Fault Tolerance in Vehicle Platooning

“…In our previous work [19], we showed that this communication latency must be accounted for to avoid collisions within the platoon during emergency braking in a dense vehicle scenario that induces both high levels of data and road traffic. Murthy and Masrur propose leveraging the space buffer between vehicles in a heterogeneous platoon during emergency braking on a flat road [10] or in a downhill [18]. To this end, the authors propose that if a platooning vehicle cannot brake at its assigned deceleration rate on a downhill road, it sends distress messages so that the other vehicles can adapt their deceleration rates to the one under distress.…”

“…In contrast, instead of dissolving the platoon, we propose to switch between controllers and/or adjust inter-vehicle gaps proportionally with the levels of communication outages in this paper. The works in [10], [19], and [18] emphasize minimizing the stopping distance of the LV in addition to avoiding collisions between the FVs to attain a fail-safe state. However, to the best of our knowledge, the transition from fail-operational states to emergency braking states leading to a fail-safe state is not considered in previous works.…”

“…Liu et al in [45] and Fernandes and Nunes in [46] show that delaying the actions of the vehicles in a platoon for a short period can help achieve synchronization, which leads to string stability in the cruising states. Murthy and Masrur also use the concept of delayed action for achieving synchronization [10], [18]; however, in the context of emergency braking rather than string stability. The authors propose that all vehicles in a platoon should wait for 20 ms before braking simultaneously.…”

“…However, it is not beneficial to maintain large inter-vehicle gaps when in a fail-safe state if it takes longer time to reach it or if it causes the LV to traverse longer. In [10], [13], [18], and [19], the authors focus on precisely this: minimizing the stopping distance of the platoon. However, until now, reaching the fail-safe state from any degraded but fail-operational state due to previously encountered problems with the wireless connectivity has not been considered.…”