This paper presents an overview of Moving Network (MN) system for fifth-generation (5G) vehicular communications. The MN system basically supports some key functions of the 3rd Generation Partnership Project (3GPP) New Radio (NR) physical layer and it will additionally introduce several technologies dedicated for the MN system. The primary use case of the MN system is to provide a millimeter-wave (mmWave)-band broad-band mobile wireless backhaul (MWB) to public transportation (e.g., city buses, express buses), enabling onboard Gigabit Wi-Fi service. In addition, the MN system will be designed to operate in the unlicensed band newly allocated by Korean government called Flexible Access Common Spectrum (FACS) to allow passengers on the public transportation to use the Gigabit Wi-Fi for free. This paper also addresses several technical challenges and a brief idea of an open-loop beam switching (BSW) technology as a viable solution to the challenges. Finally, we conduct a simple computer simulation to analyse the performance of one possible configuration of the MN system. It is observed that the MN system is severely affected by the interference from adjacent cells. Therefore, in future study, it is planned to investigate a new MN system configuration that can effectively reduce the interference received from the adjacent cells.