  Societal-scale deployment of autonomous vehicles requires them to coexist
with human drivers, necessitating mutual understanding and coordination among
these entities. However, purely real-world or simulation-based experiments
cannot be employed to explore such complex interactions due to safety and
reliability concerns, respectively. Consequently, this work presents an
immersive digital twin framework to explore and experiment with the interaction
dynamics between autonomous and non-autonomous traffic participants.
Particularly, we employ a mixed-reality human-machine interface to allow human
drivers and autonomous agents to observe and interact with each other for
testing edge-case scenarios while ensuring safety at all times. To validate the
versatility of the proposed framework's modular architecture, we first present
a discussion on a set of user experience experiments encompassing 4 different
levels of immersion with 4 distinct user interfaces. We then present a case
study of uncontrolled intersection traversal to demonstrate the efficacy of the
proposed framework in validating the interactions of a primary human-driven,
autonomous, and connected autonomous vehicle with a secondary semi-autonomous
vehicle. The proposed framework has been openly released to guide the future of
autonomy-oriented digital twins and research on human-autonomy coexistence.
