Impact of Acceleration/deceleration Limits on the String Stability of Adaptive Cruise Control

TL;DR

This paper investigates how acceleration and deceleration limits in adaptive cruise control systems affect string stability, safety, and traffic congestion, revealing that constraints can cause amplification of speed perturbations and safety risks.

Contribution

It demonstrates the significant impact of acceleration/deceleration limits on ACC string stability and safety, and suggests expanding parameter space to improve system performance.

Findings

Constrained acceleration/deceleration can cause speed overshoot and safety issues.

Marginally string stable ACCs reduce congestion and queue length.

Sequence of vehicle limits affects congestion waves and safety in mixed ACC platoons.

Abstract

This paper demonstrates that the acceleration/deceleration limits in ACC systems can make a string stable ACC amplify the speed perturbation in natural driving. It is shown that the constrained acceleration/deceleration of the following ACCs are likely to cause speed overshoot to compensate for an extra large/small spacing. Additionally, we find that the constrained deceleration limits can also jeopardize safety, as the limited braking power produces extra small spacing or even crashes. The findings are validated through experiments on real cars. The paper suggests that the ACC parameter space should be extended to include the acceleration/deceleration limits considering their significant role exposed here. Through numerical simulations of ACC platoons, we show i) a marginal string stable ACC is preferable due to the smaller total queue length and the shorter duration in congestion; ii) congestion waves in a mixed ACC platoon largely depend on the sequence of vehicles provided different acceleration/deceleration limits, and iii) the safety hazard caused by the constrained deceleration limits is more significant in mixed ACC platoons when string unstable ACCs exist.