## 6 Discussion and Conclusions  
The application of BIM to alignment-based infrastructure facilities, such as roads and railways, is being increasingly explored. However, BIM software is optimized to represent floor-based vertical buildings. In the case of railway tracks, the structures must be placed along the 3D alignment, and each element must be independently represented to facilitate information management. AMTs manage separate objects as a single unified object along the alignment; thus, they present severe limitations regarding the accurate representation of each object. Therefore, a single software cannot create all element models of different infrastructure. A modeling process employing multiple modeling software should be integrated to represent railway tracks; the interoperability of information between the employed software must be secured. In this study, a method for creating extended IFC-based models was proposed to apply BIM to railway tracks and manage information based on 3D alignment. First, continuous structures (rails and ballasts) and discontinuous structures (sleepers, fasteners, and joints) that reflect the cant were created through the linkage of discretized alignment information. Second, classification systems for each element were created. The elements such as \"IfcTrack\" and \"IfcTracksleeper\" were newly defined according to the classification systems. They include the expression of railway tracks and the properties of the structures thereof. Third, element models were matched to extended IFC entities using classification codes as identifiers. Finally, extended IFC-based information models were created by recognizing objects through classification codes, UI, and spatial information. The proposed methodology enables the actual railway track to behave as an extended IFC-based information model. The proposed method was verified upon validating the IPF, based on the extended IFCs. The proposed methodology can (a) employ functions of the existing software, (b) facilitate the creation of information models of railway tracks by linking alignment information, and (c) convert them into extended IFC schema-based information models. Its implementation can reduce the modeling  
Figure 13: IFC4-based model in Solibri Model Checker. time required for the creation of railway track information models. Other functions of the existing software can also be employed because the connecting AMT and BAT software is executed using the 3D alignment information. It is expected that the proposed methodology can also be effectively applied to create information models of other alignment-based infrastructure, such as roads. Moreover, the method enables automatic identification of components to IFC elements regardless of the type of structure. One benefit of the proposed method is that it can facilitate the development of a model of infrastructure other than railway tracks in the future. The traditional method of setting the actual location employs a local coordinate system and a reference point containing global coordinate information. The proposed methodology facilitates the creation of a model according to the actual location information because of alignment information. It is expected that the created models can be integrated with the information models of other structures. For example, it is expected that they can be linked with terrain models created from the actual terrain data or other structural models, such as railway bridges. Future research should focus on the ways in which the proposed methodology can support BIM of railways. First, the functions of the data schema for railway track representation must be proven. The railway structures have a long-life cycle with various types of data. Therefore, the generated model should include various types of information using the life cycle. Second, constraints to structures need to be further researched. The constraints are applicable between the lower and upper objects.