## 5 DT Technology in the Lifecycle of Transportation Infrastructure
### Decommissioning and Replacement Phase  
A decommissioning plan entails the systematic dismantling, replacement, or repurposing of transportation infrastructure like bridges, roads, and tunnels, upon reaching the end of their service life, presenting safety risks, or becoming obsolete. This process generally considers multiple aspects, such as structural health, impact on urban traffic, replacement options, and resource recycling or reuse. At this stage, DT technology not only provides precise assessments of conditions but also enhances the management of decommissioning and resource utilization. DT systems during the decommissioning and replacement stage offer services that include assessments for decommissioning, resource reuse, environmental impacts, and the design and testing of new facilities. As mentioned in previous sections, the continuous gathering and analysis of data, even up to the point of decommissioning, permit very accurate verification of the structural and usage conditions of the facility. This process helps to find the right timing and strategy for decommissioning. For example, in the deconstruction of the bridge [98], the application of DT simulation of different decommissioning schemes can yield the best dismantling method, which would provide the least interference to surrounding traffic and minimize safety risks. Precise evaluation and planning ensure the safety of the decommissioning process and create more favorable conditions for the subsequent construction of replacement facilities. Noise Barrier Tunnels (NBT) are composed of prefabricated members that are readily replaceable, reusable, and can offer better performance when used as replacement members. Reusing NBT members is far more cost-competitive and environmentally friendly compared to producing new members. However, one of the key challenges involves determining the remaining lifetime of existing NBT members before dismantling. To this end, [99] adopted a prototype of the NBT DT to perform condition and lifespan predictions through numerical behavior analysis for tunnel components. It can also be applied in the decommissioning process, in which DT technology supports the planning and optimization of resource reuse in decommissioned facilities [100]. For instance, through the detailed model and data incorporated, DTs are able to analyze and assess which of the building materials can be recycled or reused, and which have to undergo safe treatments. Resource reuse planning reduces [101] not only the waste generated during decommissioning but also minimizes negative environmental impacts, thereby achieving sustainability goals. A DT can simulate the environmental impacts of infrastructure decommissioning by combining sensor-based environmental data with material properties. Regarding the decommissioning process in the context of a tunnel, for example, DTs can be adopted to simulate dust and noise propagation produced during demolition, again proposing measures to reduce environmental impact while guaranteeing that decommissioning work follows the requirements related to environmental protection. After decommissioning, new facilities are often built instead. DTs also play an important role in this regard. Through virtual simulation and comparative analysis of multiple scenarios, DTs are able to help managers choose the best replacement plan and conduct ample testing in advance before construction starts. For example, in the redesign of a road or even in the replacement of a bridge, using DTs allows for the simulation of the operation of new facilities, the analysis of their impact on traffic flow, and the assessment of effects on the environment and infrastructure in general, while at the same time supporting the managers in making informed decisions prior to actually building the new facility. Together with the aforementioned factors, a significant reduction in uncertainties and risks can be achieved during the construction process by means of virtual testing with a DT.