This paper proposes a Smart Mobility Digital Twin (SMDT) platform for the control of connected and automated vehicles (CAVs) over next-generation wireless networks. The SMDT platform integrates cloud and edge computing to enable real-time traffic modeling and navigation services. The platform leverages digital twin (DT) technology to enhance traffic efficiency and road safety by providing dynamic, real-time traffic information to CAVs. A novel navigation system is designed to exploit available DT information for route planning and event-triggered re-routing. The SMDT platform and navigation system are implemented using state-of-the-art products such as CAVs and roadside units (RSUs), and emerging technologies like cloud and cellular V2X (C-V2X). Proof-of-concept (PoC) experiments are conducted to validate the system's performance. The results show that the SMDT platform can reduce average travel time and blocking probability due to unexpected traffic incidents. The peak latency for DT modeling and route planning services is 155.15 ms and 810.59 ms, respectively, which aligns with 3GPP requirements for emerging V2X use cases. The SMDT platform enables cloud services to leverage DT capabilities to enhance autonomous driving experiences. The platform's architecture includes RSU edges, CAV edges, and a central cloud, which are interconnected to support traffic DT creation, data processing, and user interaction. The CAV navigation system is designed to use an event-triggered planning strategy to dynamically re-route users in response to traffic events. The system's performance is evaluated based on traffic efficiency, safety, latency, and reliability. The results from large-scale traffic simulations show that the SMDT platform improves traffic efficiency and safety. The platform's communication requirements include reliable V2X links for data exchange between RSUs, CAVs, and the cloud. The system's design considers safety and robustness, as well as the integration of hardware, software, and communication technologies. The SMDT platform demonstrates the potential of digital twin technology in smart mobility systems, enabling real-time traffic modeling and navigation services for CAVs.This paper proposes a Smart Mobility Digital Twin (SMDT) platform for the control of connected and automated vehicles (CAVs) over next-generation wireless networks. The SMDT platform integrates cloud and edge computing to enable real-time traffic modeling and navigation services. The platform leverages digital twin (DT) technology to enhance traffic efficiency and road safety by providing dynamic, real-time traffic information to CAVs. A novel navigation system is designed to exploit available DT information for route planning and event-triggered re-routing. The SMDT platform and navigation system are implemented using state-of-the-art products such as CAVs and roadside units (RSUs), and emerging technologies like cloud and cellular V2X (C-V2X). Proof-of-concept (PoC) experiments are conducted to validate the system's performance. The results show that the SMDT platform can reduce average travel time and blocking probability due to unexpected traffic incidents. The peak latency for DT modeling and route planning services is 155.15 ms and 810.59 ms, respectively, which aligns with 3GPP requirements for emerging V2X use cases. The SMDT platform enables cloud services to leverage DT capabilities to enhance autonomous driving experiences. The platform's architecture includes RSU edges, CAV edges, and a central cloud, which are interconnected to support traffic DT creation, data processing, and user interaction. The CAV navigation system is designed to use an event-triggered planning strategy to dynamically re-route users in response to traffic events. The system's performance is evaluated based on traffic efficiency, safety, latency, and reliability. The results from large-scale traffic simulations show that the SMDT platform improves traffic efficiency and safety. The platform's communication requirements include reliable V2X links for data exchange between RSUs, CAVs, and the cloud. The system's design considers safety and robustness, as well as the integration of hardware, software, and communication technologies. The SMDT platform demonstrates the potential of digital twin technology in smart mobility systems, enabling real-time traffic modeling and navigation services for CAVs.