## 2 Introduction  
### Background  
Building information modeling (BIM) is a digital process involving the creation and management of a virtual model throughout the entire lifecycle of a construction or infrastructure project [1]. By sharing the model information, it significantly enhances work efficiency and enables collaborative management [2]. This is evident in stakeholders optimizing designs and construction processes through the visualization and simulation of construction processes, enabling the identification of potential issues [3, 4]. Moreover, it facilitates communication and coordination among architects, engineers, contractors, and owners throughout the entire construction project [3]. Despite the proven advantages of BIM applications in various studies, there remain challenges in precisely measuring the details of BIM's specific application's environmental and economic benefits during the construction phase [5].  
Several countries and organizations worldwide have developed BIM standards and guidelines to overcome challenges and promote BIM usage. For instance, the International Organization for Standardization (ISO) updated the global BIM standards in 2020 [6]. The UK has adopted three different levels of BIM standards [7], while countries like the United States, Finland, Norway, Singapore, and South Korea have issued their national BIM application standards to establish BIM working environments. These guidelines serve as blueprints for BIM implementation, assigning roles and responsibilities to various stakeholders. Despite widespread BIM applications in recent years [8], most of the literature analyzing BIM concentrates on architectural projects, with limited focus on infrastructure construction, building maintenance, and protection. In earlier publications [9], the authors explored the advantages of BIM applications in the design phase of the railway infrastructure, providing examples through quantitative research analyzing cost, work hours, and labor differences during the design phase. Additionally, qualitative research analyzed the primary tasks involved, offering insights into the application of BIM in the design phase of railway infrastructure.  
However, due to higher demands on personnel, work hours, and costs during the construction phase when compared to the design phase, whether the use of BIM in the construction phase offers advantages in terms of cost and time savings is a question that this study attempts to address. Thus, to evaluate the performance of BIM applications during the construction phase of railway infrastructure projects. To achieve this, the authors conducted in-depth investigations and interviews, collecting data on the application of BIM during the construction phase from two ongoing railway infrastructure projects and the involved BIM consulting companies. Through data analysis, a quantitative assessment was performed by comparing the cost-effectiveness, work hours, and differences in the number of workers between situations where construction companies independently used BIM and cases where professional BIM consulting services were engaged. A qualitative analysis was conducted on the specific tasks, information data, location information, software used, and other aspects of BIM participation in the work, aiming to identify the specific advantages in terms of economic benefits gained from using BIM during the construction phase of railway infrastructure projects.