# Digital Twin Framework for Road Infrastructure Management
## 1 Introduction
Generally, standards, which are formalized documents outlining best practices, play a critical role in this context. They are essential for supporting the scalable deployment of DT solutions [10]. Specifically, voluntary standards provide specifications, procedures, and guidelines to ensure the safety, consistency, and reliability of products, services, and systems [11]. To be truly effective, these standards must be applicable across diverse business domains and aligned with a shared set of processes and use cases to facilitate interoperability within the DT ecosystem [12]. Therefore, standards serve as foundational tools for enabling successful DT implementation [13]. A key principle for future DT standards is that they should be open, enabling the extension and reuse of existing standards when necessary [14]. Moreover, developing interoperability standards--along with reference models, architectures, and protocols--is crucial for integrating interconnected DT systems within a diverse ecosystem [15]. As the literature suggests, the core gaps and some requirements regarding DT-related standards and models can be identified as follows:  
* Absence of unified frameworks and standards that support interoperability and seamless data exchange;
* Lack of common data standards and tools that can provide interoperability;
* Absence of standards and interfaces, as well as inconsistencies in modeling approaches;
* Lack of standardized DT implementation in the AEC industry due to project-specific development;
* Lack of DT implementation that encompasses all phases, from initial planning to execution;
* Need for DT standards that are applicable across business domains to facilitate interoperability within the DT ecosystem;
* Need for DT interoperability standards that include reference models, architectures, and protocols for enabling connected DT systems within an ecosystem;
* Need for open DT standards, which can be developed by extending and reusing existing standards. Therefore, a common data standard that would provide openness, interoperability, and data exchange and cover the whole lifecycle of the assets, as well as connecting with other DTs using a consistent modeling approach, is required. Considering the research gaps identified and the relevant requirements for developing DTs, this study aims to explore existing initiatives and works to derive a comprehensive DT framework that can serve as a common foundation and reference model for implementing DTs, particularly for road infrastructure management. Consequently, this study aims to examine existing DT applications in road infrastructure, including roads, bridges, tunnels, and other civil infrastructures, to develop a DT framework (reference model) that can support future standardization efforts in the domain. To achieve this objective, this study identifies existing standards and models currently employed for DT adoption and implementation in road infrastructure management, analyzing their structures and functional components. It further presents the DT framework and its core functional elements, designed to be applicable across a wide range of road infrastructure scenarios. The results of this work will serve as a reference document to support standardization efforts and provide the requirements for implementing DTs in road infrastructure. Additionally, the comprehensive framework provided can be leveraged as a foundational basis for integrating multiple DTs, such as network-level road management, rather than focusing on a single asset or component. This approach will also contribute to the establishment of a DT ecosystem within the field. To achieve the research objectives, the following research questions (RQs) are formulated:  
RQ1--What is the current status of standards development related to DTs? RQ2--What DT frameworks or reference models/architectures are being used in current road infrastructure initiatives, and what are their structures/layers and components?