Interaction between humans and autonomous systems: Human facing
 explanatory interface for an urban autonomous passenger ferry

Problem statement During a public trial, over 150 passengers were interviewed about their thoughts and experiences using an autonomous ferry, among over 1500 passengers taking a trip on the world's first autonomous urban passenger ferry in Trondheim. One of the main issues expressed by passengers was a lack of information about the state of the unmanned ferry service. A safety attendant was aboard for the three-week public testing to take over control in the unlikely case of a hazardous event. Observations of passengers revealed a desire for information regarding the functionality of the ferry, the current state of the boat, and the progress of the current journey. Passengers interviewed stated that, especially if no safety personnel are on board, the demand for information is higher because no one can be queried. The absence of information increased the sense of insecurity. Since the space aboard the autonomous passenger ferry is limited, the used option cannot be too spacious; nonetheless, the information must be easily available to users. Research Question What information do passengers require on a self-driving urban passenger ferry? Does the type of information displayed affect passengers' perceptions of safety? Method Two 10-inch high-luminance (1000 nits) screens have been installed on the mast of the autonomous passenger ferry, allowing the user to see information on both sides when embarking, disembarking, and traveling. Two distinct information screen concepts have been visualized for use in a semi-structured interview. First, the passengers were asked what they could see on each of the concepts and what information they thought would be most useful. They should also explain how the information they view influences their sense of safety and trust. In an AB-test, passengers were asked to select a preferred concept for the information screen and describe why they chose that concept in detail. One of the concepts (A) was straightforward and depicted the journey's progress as a linear bar. Furthermore, the traveler could observe the ferry's status with a large illustration, along with the status in one word and a brief description. The second concept (B) should attract those passengers who are interested in details and technical elements. Concept B contained an environment map with the ferry's intended path and present position and heading, details for each single thruster, the speed in kn, system health status, battery levels, compass, object detection, and the ferry's current operation status. All used and previously stated characteristics on both presented screens have been used in a semi-open card sort to determine which information is most valuable to the passengers. The passengers were instructed to prioritize the offered information and fill in blank cards with missing information. Each of the placed cards was awarded points based on their location in the assortation; the further left the things were placed, the more points were awarded; the further right, the fewer points were awarded. Results 15 of the 1500 passengers who participated in the public trial of the urban autonomous passenger ferry were specifically asked about their preference for data visualization and the demand for information on such a ferry. The majority of the passengers (n = 12) indicated that they would prefer the simpler version of the information concept (A), whereas the remainder of the interviewed passengers would prefer the more technical interface because they are more concerned with the ferry's functionality and the reliability of the components. All of the users stated that they would feel less safe if there was no safety attendant or information screens on board. The cart sort analysis reveals that the more technical components have been ranked as less relevant, with the ferry's state, system health, and continuous travel progress being more important than detected objects, thruster details, LiDAR, and radar visualization. Conclusion Both the interview data and the card sort revealed that passengers on autonomous passenger ferries have a higher demand for straightforward and immediately available information. If they cannot obtain it from a human safety attendant on board, they require additional information that is not overly technical in order to maintain a high degree of safety perception.