  In automotive user interface design, testing often starts with lab-based
driving simulators and migrates toward on-road studies to mitigate risks. Mixed
reality (XR) helps translate virtual study designs to the real road to increase
ecological validity. However, researchers rarely run the same study in both
in-lab and on-road simulators due to the challenges of replicating studies in
both physical and virtual worlds. To provide a common infrastructure to port
in-lab study designs on-road, we built a platform-portable infrastructure,
Portobello, to enable us to run twinned physical-virtual studies. As a
proof-of-concept, we extended the on-road simulator XR-OOM with Portobello. We
ran a within-subjects, autonomous-vehicle crosswalk cooperation study (N=32)
both in-lab and on-road to investigate study design portability and
platform-driven influences on study outcomes. To our knowledge, this is the
first system that enables the twinning of studies originally designed for
in-lab simulators to be carried out in an on-road platform.
