This paper presents a novel Smart Mobility Digital Twin (SMDT) platform for controlling connected and automated vehicles (CAVs) over next-generation wireless networks. The SMDT platform integrates cloud and edge computing resources to enhance traffic efficiency and road safety. A CAV navigation system is designed to exploit available DT information, enabling event-triggered route planning to avoid traffic incidents. The platform is implemented using state-of-the-art products and emerging technologies, including CAVs, roadside units (RSUs), cloud, and cellular V2X (C-V2X). Proof-of-concept (PoC) experiments and large-scale traffic simulations are conducted to validate the system's performance. The results show that the SMDT platform reduces average travel time and blocking probability due to unexpected traffic incidents, with peak overall latency for DT modeling and route planning services of 155.15 ms and 810.59 ms, respectively, meeting 3GPP requirements. The demonstration video is available at https://youtu.be/3waQwlaHQkk.This paper presents a novel Smart Mobility Digital Twin (SMDT) platform for controlling connected and automated vehicles (CAVs) over next-generation wireless networks. The SMDT platform integrates cloud and edge computing resources to enhance traffic efficiency and road safety. A CAV navigation system is designed to exploit available DT information, enabling event-triggered route planning to avoid traffic incidents. The platform is implemented using state-of-the-art products and emerging technologies, including CAVs, roadside units (RSUs), cloud, and cellular V2X (C-V2X). Proof-of-concept (PoC) experiments and large-scale traffic simulations are conducted to validate the system's performance. The results show that the SMDT platform reduces average travel time and blocking probability due to unexpected traffic incidents, with peak overall latency for DT modeling and route planning services of 155.15 ms and 810.59 ms, respectively, meeting 3GPP requirements. The demonstration video is available at https://youtu.be/3waQwlaHQkk.