## 5 DT Technology in the Lifecycle of Transportation Infrastructure
### Operation and Management Phase  
During the operational phase, transport infrastructures such as roads, bridges, and tunnels are constantly subjected to traffic flow and environmental pressures. Traditional management models mainly depend on periodic inspections and reactive maintenance. These efforts have been handicapped by a serious lack of real-time data, significant theoretical limitations, and post-event maintenance. The DT can accurately monitor and horizontally control the dynamic state of key parameters, including traffic flow and equipment status. The main applications of DTs at this stage involve the real-time monitoring of traffic flow, assessment of equipment status, optimization of maintenance, and support for emergency management. According to the data analysis, it is possible to forecast the wear of infrastructure components to estimate the timing of future failures. The advantage of this approach over traditional regular maintenance is that it allows the maintenance team to intervene only when necessary, thereby reducing unnecessary activities and minimizing downtime. DT systems in the operation and management phase of infrastructure offer services that include real-time traffic monitoring and dispatch optimization, as well as equipment status monitoring and predictive maintenance. In road, bridge, and tunnel traffic management, DT technology enables real-time monitoring and management of traffic flow, vehicle speed, and congestion data, thus enhancing traffic efficiency and safety [79]. Ref. [80] highlighted data-driven decision-making approaches, emphasizing the importance of timely and informed decisions based on accurate data, as well as the application of DT technology in infrastructure resilience and disaster management. Traffic facility simulation enables the modeling [81] and optimization [82] of urban traffic networks, identifying bottlenecks and providing congestion simulation and optimization services. By simulating traffic operations under different strategies and scenarios, DTs assess the effects of traffic planning and infrastructure modifications, offering decision support and optimization recommendations to improve traffic fluidity, reduce congestion, and increase operational efficiency. Transportation infrastructure interconnection entails the integration, interaction, and collaborative connection of multisource heterogeneous data. It links data from various transportation facilities and systems using identifiers like GIS feature codes, geographic entity codes, BIM model codes, and IoT codes. This method associates spatial information and static attribute information of urban transportation infrastructure with related performance state indicators, materials, algorithm output metrics, sensor information, location data, and model spatial structure information, facilitating data sharing and collaboration to enhance traffic management and decision-making. Additionally, this interconnected framework allows for detailed visual modeling of people, vehicles, roads, hubs, auxiliary facilities, and the environment. Through high-fidelity visual representation, simulation models not only accurately replicate traffic flow and behavior but also vividly reproduce the complexity and diversity of the traffic environment. These models aid in situational awareness and dynamic data display, depicting in real time key performance indicators such as vehicle and pedestrian micro-traffic behaviors, traffic flow, speed, waiting time, delays, queue length, signal states, accident information, and the interconnected status of various facilities [67; 83; 84]. Monitoring equipment status in transportation infrastructure operation is vital for ensuring stability. Data collected by sensors--including bridge vibration frequencies, humidity, and tunnel temperatures [85], along with the conditions of road wear--are transmitted in real-time to the DT model, facilitating the dynamic portrayal of the facility's current state [86].