# Digital Twin Framework for Road Infrastructure Management
## 4 Digital Twin Framework for Road Infrastructure Management
### Proposed Digital Twin Framework for Road Infrastructure Management
#### 4.3.5 Users/User Interface Layer
It provides a virtual representation of the OMEs within the DT and hosts various applications and services, which are organized into three main sub-domains: O&M, application and service, and resource access and interchange. The O&M sub-domain contains information about the OME and includes digital modeling, presentation and representation, maintenance, and synchronization of FEs. The application and service sub-domain consists of simulation, analytic service, reporting, and application support FEs. The resource access and interchange sub-domain facilitates information exchange between the DT core and the user domain, providing functions such as interoperability support, access control, plug-and-play support, and peer interface. In the proposed model, the data/digital modeling layer corresponds to the O&M sub-domain. Specifically, this layer contains digital representations of physical assets or entities, which are categorized and stored within corresponding data models based on their characteristics. It primarily represents information related to physical assets, including geometric properties, behaviors, characteristics, and attributes, similar to the digital modeling FE in the manufacturing framework. Therefore, the models within the data/digital modeling layer align with the digital modeling FE and encompass various types, such as GIS, BIM, and CIM, as illustrated in Figure 6.  
The data analytics/application layer in the proposed model offers a range of functionalities, including road asset management, maintenance strategy, transportation management, simulation, evaluation and assessment, visualization, monitoring, control, and alert functions (Figures 6 and 9). These functionalities generally align with the roles of the FEs within the O&M and application and service sub-domains of the manufacturing framework. Table 6 compares these functionalities, with the data analytics/application layer denoted as \"DA\" and the data/digital modeling layer as \"DM.\" This comparison is based on the definitions of each FE in the manufacturing and proposed models, with specific components illustrated in Figure 9.  
However, not all of the features and functionalities of the proposed model correspond directly to those of the manufacturing model. This comparison aims to facilitate a clearer understanding of the proposed model, especially for readers already familiar with the ISO 23247-2 DT reference model. This study presented results from a functional modeling perspective rather than a procedural or process modeling standpoint. Accordingly, Table 6 includes only the currently relevant functional elements for comparison. Future studies can thus focus on the internal FEs of DTs, specifically those already identified within the manufacturing framework, such as the resource access and interchange sub-domain and the cross-system sub-domain, which provide common functionalities like data translation, assurance, and security support. Lastly, the user domain in ISO 23247-2 hosts applications and services that support the analysis and utilization of DT models by both humans and machines. This domain facilitates HMI, where users can include humans, devices, applications, or systems that utilize DT applications and services. Specifically, when users are using existing enterprise applications, they may appear as a manufacturing execution system, an enterprise resource planning system, or other DTs. The service/UI layer of the proposed model enables users to interact with DTs through functionalities such as data input, control, asset monitoring, and DT management. These interactions can be carried out via various platforms, including web portals, desktop and mobile applications, or in individual or mixed forms of VR/AR/MR/XR. Thus, similar to ISO 23247-2, this layer supports diverse analyses and simulations to inform decision-making processes. Furthermore, consistent with the manufacturing framework, users can be systems and machines, not only humans, depending on the implementation purposes.