Comparing state-of-the-art and emerging augmented reality interfaces for autonomous vehicle-to-pedestrian communication

In the last few years, a considerable literature has grown around the theme of how to provide pedestrians and other vulnerable road users (VRUs) with a clear indication about a fully autonomous vehicle (FAV)'s status and intentions, which is crucial to make FAVs and VRUs coexist. So far, a variety of external interfaces leveraging different paradigms and technologies have been created. Proposed designs include vehicle-mounted devices (like LED panels), short-range on-road projection, and road infrastructure interfaces (e.g., special asphalts with embedded displays). These designs have been experimented in different settings, using mockups, specially prepared vehicles, or virtual environments, with heterogeneous evaluation metrics. Some promising interfaces based on Augmented Reality (AR) have been proposed too, but their usability and effectiveness have not been tested yet. This paper aims to complement such body of literature by presenting a comparison of state-of-the-art interfaces and new designs under common conditions. To this aim, an immersive Virtual Reality-based simulation was developed, recreating a well-known scenario used in previous works represented by pedestrian crossing in urban environments under non-regulated conditions. A user study was then performed to investigate the various dimensions of vehicle-to-pedestrian interaction in both objective and subjective terms. Results showed that, although an interface clearly standing out over all the considered dimensions does not exists, one of the studied AR designs was able to provide state-of-the-art results in terms of safety and trust, at the cost of a higher cognitive effort and lower intuitiveness compared to LED panels showing anthropomorphic features. Together with rankings on the various dimensions, indications about advantages and drawbacks of the various alternatives that emerged from the study could be an important information source for next developments in the field