In this poster, we investigate novel user-centered methods and techniques for cross-virtuality user journeys for designing in-vehicle experiences. We argue that rapid prototyping of automotive human-machine interfaces (HMIs) can be achieved with mixed reality technology along the reality-virtuality (RV) continuum. For example, standalone virtual reality (VR) head-mounted displays (HMDs) coupled with hand-worn controllers can be utilized to prototype AR interfaces such as windshield displays (WSDs) in order to facilitate an increased level of visual and spatial perception. Subsequently, the prototyped design in VR could be transferred to an AR interface (e.g., using an AR HMD) for further refinements in real-world settings. We believe that transitional interfaces in the automotive domain have the potential to fundamentally improve the design and development of novel in-vehicle visualization and interaction modalities, as well as to enhance user-centered and non-driving related collaborative activities for automated vehicles.