Safety and experience of other drivers while interacting with automated vehicle platoons

Aramrattana, Maytheewat; Habibovic, Azra; Englund, Cristofer · 2021 · Crossref

DOI: 10.1016/j.trip.2021.100381

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Summary

This study investigates how drivers of manually operated passenger cars perceive and interact with automated vehicle platoons during highway merging scenarios. While the technical benefits of platooning, such as improved traffic efficiency and energy savings, are well-documented, there is a significant lack of knowledge regarding the socio-technical aspects, specifically how other road users experience these formations. The research addresses three primary questions: how manual drivers experience interactions with automated platoons, how inter-vehicular gap sizes affect safety and experience, and whether external human-machine interfaces (eHMI) are needed to facilitate safe interactions. The study focuses on highway on-ramp merging, a context identified as potentially challenging due to the risk of manual drivers cutting into platoons, which can split the formation and compromise safety. The researchers conducted a driving simulator experiment involving 16 participants aged 20 to 65, all holding valid driving licenses. Using a high-fidelity simulator at the Swedish National Road and Transport Research Institute, participants drove a passenger car on a 500-meter on-ramp and encountered a platoon of five automated passenger cars traveling at 120 km/h. The study employed a within-subjects design with one independent variable: the inter-vehicular gap between platooning vehicles. Four gap sizes were tested: 15 m, 22.5 m, 30 m, and 42.5 m, corresponding to time gaps of approximately 0.5 to 1.3 seconds. Each participant experienced each gap size twice in a randomized order, resulting in eight experimental runs per driver. Data collected included quantitative metrics such as the number of cut-ins and crashes, as well as qualitative assessments of perceived safety, comfort, mental effort, and merging ease. The results indicated that drivers generally found interactions with automated platoons to be mentally demanding, unsafe, and uncomfortable. Participants commonly expected the platoon to adapt its behavior to accommodate a smooth merge. The size of the inter-vehicular gap significantly influenced these outcomes. Larger gaps (30 m and 42.5 m) resulted in a better overall experience, more frequent cut-ins, and fewer crashes compared to shorter gaps (15 m and 22.5 m). Drivers expressed a need for additional information about the platoon to better anticipate its behavior and avoid cutting in. The findings suggest a design trade-off: shorter gaps combined with external HMI could communicate the platoon’s intent to stay together, thereby preventing cut-ins. Conversely, if the goal is to facilitate frequent, safe, and pleasant cut-ins, gaps larger than 22.5 m are more suitable. The significance of this study lies in its contribution to the understanding of social acceptance and safety implications of automated vehicle platoons. It highlights that while platooning offers technical advantages, it introduces new interaction challenges for manual drivers, particularly during merging. The study underscores the importance of considering user experience and perceived safety in the design of platooning systems. It suggests that external communication methods, such as eHMI, may be necessary to clarify platoon intent and reduce uncertainty for other road users. The authors conclude that further research is needed to thoroughly inform design decisions regarding gap sizes and communication strategies to ensure safe and efficient integration of automated platoons into mixed traffic environments.

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