Safety Effects of Connected and Automated Vehicle-Based Variable Speed Limit Control near Freeway Bottlenecks considering Driver’s Heterogeneity

Ye Li,Yuntao Shi,Baojie Wang,Chen Yuan,Jaeyoung Lee

doi:10.1155/2022/7996623

Abstract

A control strategy using variable speed limit (VSL) is a proven solution to reduce freeway collision risks and improve safety. However, the heterogeneity of human drivers restricts the effectiveness of traditional VSL controls, which may be made up by recent advanced technologies of connected and automated vehicles (CAVs). This study aims to propose a CAV-based VSL control system to address the limitations caused by human drivers on VSL control’s effectiveness. First, the heterogeneity of human drivers is analyzed, and its impact on the safety performance of VSL is examined. Specifically, a microscopic simulation platform is established, and two vehicle dynamic models developed for CAVs and human-driven vehicles (HDVs) are incorporated into the simulation platform. Based on a widely utilized surrogate safety measurement, time-to-collision, its derivative metrics are applied to evaluate collision risks, and the total travel time is used to assess operational efficiency. Extensive simulations are conducted to examine the performance of the proposed CAV-VSL system. The results indicate the following: (1) the heterogeneity of human drivers negatively affects the performance of the VSL; (2) the performance of the proposed control system in a mixed flow can be improved by advanced wireless communication technology; (3) CAVs are able to implement the VSL control strategy effectively resulting in the proactive reduction of the heterogeneity.

Highlights

Freeway bottlenecks have attracted considerable attention from transportation researchers since the bottlenecks drastically reduce both efficiency and safety [1,2,3,4,5]. e formation of traffic bottlenecks is caused by a variety of reasons, such as lane capacity reduction, temporary lane closure, and crashes. e speed of vehicles downstream reduces when approaching the bottleneck area and a shockwave is propagated to the upstream, which increases rear-end collision risks of upstream vehicles
Results of the Safety Impact of the connected and automated vehicles (CAVs)-variable speed limit (VSL) System. e traffic flow consisting of all human-driven vehicles (HDVs) without any control strategies was firstly simulated as the base case. en, different CAV market penetration rate (MPR) and VSL control were tested and results of safety impacts are displayed in Figure 5. e horizontal axes are time exposed TTC (TET)∗ and time-integrated TTC (TIT)∗, which are normalized results of TET and TIT and can be calculated as follows: TET∗
When CAV MPR is 0%, the VSL control achieves the reductions of 56% and 59% in TET∗ and TIT∗, respectively. e above results indicate that both CAV and VSL

Summary

Introduction

Freeway bottlenecks have attracted considerable attention from transportation researchers since the bottlenecks drastically reduce both efficiency and safety [1,2,3,4,5]. e formation of traffic bottlenecks is caused by a variety of reasons, such as lane capacity reduction, temporary lane closure, and crashes. e speed of vehicles downstream reduces when approaching the bottleneck area and a shockwave is propagated to the upstream, which increases rear-end collision risks of upstream vehicles. E speed of vehicles downstream reduces when approaching the bottleneck area and a shockwave is propagated to the upstream, which increases rear-end collision risks of upstream vehicles. In order to mitigate the rear-end collision risks caused by freeway bottlenecks, various safety management countermeasures have been implemented in practice, such as variable speed limit (VSL) control, ramp metering, managed lanes dynamic routing, and hard shoulder running [2, 4,5,6,7,8,9,10,11]. E core idea of VSL is to proactively adjust vehicles’ speeds upstream and reduce the speed difference of vehicles between the upstream and downstream parts, so as to decrease rear-end collision risks [13, 14]. Some drivers do not comply with the variable speed limit, while other conservative drivers have an overcompliance behavior and reduce to an excessively low speed. e abovementioned heterogeneity issues may negatively impact the performances of VSL control strategies in practice

Objectives

Results

Conclusion