## 5 DT Technology in the Lifecycle of Transportation Infrastructure  
The entire lifecycle [64] refers to the complete process a product or system undergoes, from design and manufacturing to testing, operation, and maintenance, covering all stages from conceptualization to decommissioning. During the lifecycle, it is highly important not only to focus on initial design and production but also to continuously monitor operation, maintenance, and upgrades to achieve performance, reliability, and safety. The whole lifecycle for DT systems in urban transportation infrastructure includes all phases, starting from the very beginning with planning and design to construction and implementation, followed by operation and management, maintenance and upgrades, and concluding with decommissioning and replacement. In this lifecycle, DT technology can provide comprehensive intelligent services under real-time conditions for transportation infrastructure management and optimization. Guidance on integrating the technology of a DT into urban transportation infrastructure includes comprehensive innovations. It helps planners intuitively understand the layout and identify strengths or weaknesses in transportation infrastructure through high-precision virtual models during the early planning and design stages. Additionally, it can simulate various problems that may arise, along with outcomes from several alternate plans during real operation to optimize design decisions. During the construction and implementation phase, DT technology, in conjunction with IoT, sensors, and drones, analyzes continuous feedback data, thereby offering real-time capabilities for monitoring construction status and proactive risk forecasting. This allows for the precise management of engineering quality and schedules while minimizing the possibility of human error. The operation and management phase mainly involves the real-time monitoring and optimization of dispatching in response to the long operational pressures faced by urban transportation facilities due to rapidly growing traffic flow in modern cities. At this stage, DT technology leverages virtual-physical mapping to facilitate the real-time monitoring and dynamic simulation of transportation infrastructure. This ranges from monitoring the flow of traffic and facility conditions to carrying out safety checks to ensure that the whole operation process is continuous, efficient, and safe. Additionally, DT technology offers structural health monitoring for critical structures such as bridges and tunnels that can support the early detection of potential safety hazards, thereby facilitating preventive maintenance. Considering this, by the time of the maintenance-upgrade phase, most conventional transportation infrastructures rely on routine inspections and manual repairs, which usually fail to enable timely responses to sudden failures. Based on historical data analysis and machine learning algorithms, DT technology can predict the aging and damage trends of facilities and provide precise and appropriate suggestions for maintenance in advance in order to avoid sudden downtime or severe failures. This capability extends the service life of transportation infrastructure and further reduces the cost of maintenance. DTs in the decommissioning and replacement phase assist the city manager in making an accurate assessment of the current condition and future potential of transportation infrastructure--like bridges, roads, and tunnels--when it approaches its design lifespan, presents safety hazards, or no longer meets the demands of modern urban development. This is achieved through detailed analysis in real time as well as historical data. With the help of DTs' virtual simulation capability, it is possible to simulate the impact of decommissioning on surrounding traffic and urban operations in order to come up with a much more reasonable decommissioning plan that ensures safety throughout the process with minimal impact on the city.