The Matter of How and When: Comparing Explicit and Implicit Communication Strategies of Automated Vehicles in Bottleneck Scenarios

The introduction of automated vehicles (AVs) leads to mixed traffic where the AV should safely and efficiently integrate into established interactions. Since the driving behavior and thus the AV's communication may differ from that of traditional road users, highly comprehensible communication strategies are needed to reliably convey the AV's intention. This work investigates the encounter of an AV and a simultaneously oncoming human driver at bottlenecks due to double-parked vehicles on both sides of the road. Regarding this scenario, we aim to answer how and when the AV should communicate right-of-way to ensure safe and efficient interactions. In a driving simulator study, 31 participants experienced eight different communication strategies in which the AV communicated explicitly via an external human-machine interface simultaneously and separately to an implicit lateral vehicle movement. Furthermore, the AV triggered its communication based on human choice reaction time. Results show that AVs should communicate right-of-way explicitly and implicitly together while not changing their maneuver to ensure safety and increase efficiency. This combined approach was rated highly comprehensible, avoided crashes, and increased participants' passing times by shortening human decision time. In addition, triggering the communication based on human choice reaction time enables the human driver to react appropriately.