  Digital Twin is an emerging technology that replicates real-world entities
into a digital space. It has attracted increasing attention in the
transportation field and many researchers are exploring its future applications
in the development of Intelligent Transportation System (ITS) technologies.
Connected vehicles (CVs) and pedestrians are among the major traffic
participants in ITS. However, the usage of Digital Twin in research involving
both CV and pedestrian remains largely unexplored. In this study, a Digital
Twin framework for CV and pedestrian in-the-loop simulation is proposed. The
proposed framework consists of the physical world, the digital world, and data
transmission in between. The features for the entities (CV and pedestrian) that
need digital twining are divided into external state and internal state, and
the attributes in each state are described. We also demonstrate a sample
architecture under the proposed Digital Twin framework, which is based on
Carla-Sumo Co-simulation and Cave automatic virtual environment (CAVE). A case
study that investigates Vehicle-Pedestrian (V2P) warning system is conducted to
validate the effectiveness of the presented architecture. The proposed
framework is expected to provide guidance to the future Digital Twin research,
and the architecture we build can serve as the testbed for further research and
development of ITS applications on CV and pedestrians.
