Safety analysis of freeway on-ramp merging with the presence of autonomous vehicles

Jie Zhu,Ivana Tasic

doi:10.1016/j.aap.2020.105966

Abstract

Freeway on-ramp merging areas are high-risk areas for motor vehicle crashes and conflicts due to the variety of driving styles, the difference in mainline and ramp traffic states, and factors related to roadway design and traffic control. The emerging Autonomous Vehicle (AV) technologies are expected to bring substantial improvements in ramp merging operations in general, including the possibility to reduce traffic conflicts and crashes by partially or fully eliminating the critical factors related to the human drivers. In order to investigate the potential safety impacts of AVs at on-ramp merging, this study first proposes a novel conflict index in theory as a specific indicator for ramp merging safety. Then, a merging conflict model is introduced to estimate the index value in various cases by considering the interactions between the mainline and ramp vehicles. In order to account for real-world uncertainties and variations in various crash-contributing factors, the proposed approach incorporates Monte-Carlo method and probabilistic distributions calibrated on the empirical freeway data. The developed approach is later applied in a case study with incremental AV market penetration rates to investigate AV safety impacts at on-ramp merging. The results show clear benefits of AVs in reducing the frequency and severity of the critical merging events. In addition, a sensitivity analysis on essential model parameters shows that the merging safety of AVs is closely related to their gap acceptance policy and the proper functioning of the driving systems, providing further insights into the future development of AVs.

Highlights

The results of Shapiro-Wilk tests reject the normality of the Con flicting Merging Headway (CMH) distributions (Table 3a), and the results of the two-sample Kolmogorov–Smirnov tests show that the distributions under different Autonomous Vehicle (AV) penetration rates are statistically different from each other (Table 3b)
This paper proposes a method to capture and assess the risk of critical events at freeway on-ramp merging with a consideration of AV presence in the traffic flow
A new conflict index that is primarily designed for the lateral merging conflicts, called Conflict Merging Headway (CMH), is proposed in theory, and a merging conflict model is developed to esti mate the value of CMH by considering the interactions between an Ramp Merging Vehicle (RMV) and an Mainline Following Vehicle (MFV) in various situations

Summary

Introduction

Many studies have been conducted to assess the safety impacts of AVs in various situations, such as the (signalized or unsignalized) in tersections (Li et al, 2013; Morando et al, 2018), roundabouts (Mor ando et al, 2018), freeway corridors (Jeong et al, 2017; Papadoulis et al, 2019), and at the traffic network level (Kockelman et al, 2016). All these studies report a remarkable reduction in the number of traffic conflicts with the presence of AVs, especially at a high AV market penetration rate. AVs’ safety perfor mance in various types of traffic bottlenecks have been well discussed in the literature, there are only very few studies focusing on AVs’ driving behaviors and the resulted safety consequences in the freeway on-ramp merging bottlenecks

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Results

Conclusion