Reachability Analysis for FollowerStopper: Safety Analysis and Experimental Results

TL;DR

This paper uses reachability analysis to verify and improve the safety of the FollowerStopper traffic control algorithm, demonstrating its limitations and proposing a safer, more human-like version based on empirical data.

Contribution

It applies reachability analysis to assess and enhance the safety of the FollowerStopper, extending previous bounds to higher speeds and proposing a modified controller for better safety.

Findings

FollowerStopper is safe under distance-based criteria.

It follows too closely compared to human drivers at higher speeds.

A modified FollowerStopper aligns better with human driving behavior.

Abstract

Motivated by earlier work and the developer of a new algorithm, the FollowerStopper, this article uses reachability analysis to verify the safety of the FollowerStopper algorithm, which is a controller designed for dampening stop- and-go traffic waves. With more than 1100 miles of driving data collected by our physical platform, we validate our analysis results by comparing it to human driving behaviors. The FollowerStopper controller has been demonstrated to dampen stop-and-go traffic waves at low speed, but previous analysis on its relative safety has been limited to upper and lower bounds of acceleration. To expand upon previous analysis, reachability analysis is used to investigate the safety at the speeds it was originally tested and also at higher speeds. Two formulations of safety analysis with different criteria are shown: distance-based and time headway-based. The FollowerStopper is considered safe with distance-based criterion. However, simulation results demonstrate that the FollowerStopper is not representative of human drivers - it follows too closely behind vehicles, specifically at a distance human would deem as unsafe. On the other hand, under the time headway-based safety analysis, the FollowerStopper is not considered safe anymore. A modified FollowerStopper is proposed to satisfy time-based safety criterion. Simulation results of the proposed FollowerStopper shows that its response represents human driver behavior better.