## 2 Limitations of Railway Infrastructure Information Model Creation Methods  
One of the important differences between information model creation methods for infrastructure and buildings is the reference line for modeling. For example, in building-oriented 3D information modeling, objects are stacked level-upon-level based on a fixed area, whereas for road and railway facilities, objects are arranged and represented based on 3D alignment. The combination of various parameters along the direction of alignment or the line perpendicular to the alignment affects the shapes and arrangements of structures. Therefore, sufficient capacity must be provided to implement alignment and structure arrangements simultaneously and manage such information.  
This type of railway alignment can be created using BIM tools, as illustrated in Figure 1a; however, it is inefficient for the representation of railway alignment for the following reasons:  
1. Railway alignment is designed using horizontal and vertical curves composed of straight lines, curves, and transition curves. BATs predominantly employ straight lines and circular curves but do not provide functions for combining the horizontal and vertical lines. Therefore, railway alignment information cannot be represented using such tools and is also not suitable for representing the shapes of structures that belong to the alignment.
2. While buildings are designed based on the floor concept in a direction perpendicular to the ground, railway track structures are arranged using 3D alignment. Therefore, alignment information must be well-represented for railway track structures, and the information must be linked with such structures. However, with BAT software, it is difficult to create an alignment that includes railway alignment information and further link this information with the created structure.  
Figure 1: Software representation of railway track: (**a**) A railway model based on building information modeling authoring tools (BATS); (**b**) a railway model based on alignment-centered modeling tools (AMTs).  
AMT software that supports infrastructure alignment provides an environment in which straight lines, transition curves, and circular curves can be created as a single object [29]. Then, they construct a model using the two-dimensional (2D) cross-sections of the structures to be modeled in 3D, such as rails and roadbeds, as reference cross-sections. A method for creating solids by sweeping along the alignment is depicted in Figure 1b [30]. This method is effective for continuous objects, such as rails and ballasts; however, it presents the following limitations in terms of accurate representation of discontinuous objects, such as sleepers, fasteners, and joints.  
1. Railway alignment does not incorporate parameters for discontinuous objects, such as sleepers; instead, it considers them as a part of the continuous alignment. Therefore, the process of extracting parameters to be applied directly to sleepers is complicated.
2. Problems regarding arrangement occur for discontinuous objects that follow 3D curves; it is difficult to generalize and reflect information regarding the angle between sleepers and the alignment, which is applied as a design parameter using AMTs. For example, the cant must be calculated at the location of each sleeper because this varies depending on its location in the alignment; however, it is difficult for AMTs to reflect the cant because AMTs cannot accurately represent discontinuous structures.  
A method for linking AMTs and BATs is proposed herein to accurately represent railway tracks and related objects using information models and to modify or utilize such information where necessary. This method enables the realization of efficient AMTs and BATs for design parameter management and object management, respectively. The detailed methodology is described in the next section.