Summary: Autonomous vehicles will have to coordinate their behavior with human road users such as drivers and pedestrians. The majority of recently proposed solutions for autonomous vehicle-to-human communication consist of introducing additional visual cues (such as lights, text and pictograms) on either the car's exterior or as projections on the road. We argue that potential shortcomings in the visibility (due to light conditions, placement on the vehicle) and immediate understandability (learned, directive) of many of these cues make them alone insufficient in mediating multi-party interactions in the busy intersections of day-to-day traffic. Our observations of real-world human road user behavior in urban intersections indicate that movement in context is a central method of communication for coordination among drivers and pedestrians. The observed movement patterns gain meaning when seen within the context of road geometry, current road activity, and culture. While all movement communicates the intention of the driver, we highlight the use of movement as gesture, done for the specific purpose of communicating to other road users and give examples of how these influence traffic interactions. An awareness and understanding of the effect and importance of movement gestures in day-to-day traffic interactions is needed for developers of autonomous vehicles to design forms of human-vehicle communication that are effective and scalable in multi-party interactions.

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Abstract-Connected Cruise Control (CCC) is an in-car driver support systems that aims to improve throughput in dense motorway traffic by advising drivers how to drive. The system is currently under development within a HTAS project. It will integrate lane advice, headway advice and speed advice. CCC will not take over vehicle control. This makes its effectiveness dependent on the drivers ability and willingness to comply to the advice. In the present study we used a thinkaloud protocol, during the first on-road field-test of the CCC system, to assess drivers' initial reactions to the advice. From the transcripts we extracted factors that can influence compliance to tactical driver advice. These factors can be used to formulate hypotheses about driver compliance to CCC.