## 1 Introduction
### Related Work
#### 1.1.1 Regional Integration of Sustainable Public Transportation  
In the last two decades, the European Commission funded several projects aiming at integrating public transport data and multimodal travel information [3]. The projects pursued the development of concepts, platforms, and finally the networking of actors from several European regions. The result of these efforts are distributed solutions for multimodal travel planning and travel-information-management solutions. The latest achievements provide integrated platforms for accessing high-quality travel information, enabling door-to-door route planning across borders, operators, and modes. With such systems, travellers can easily plan their entire trip and focus on their travel needs instead of searching for relevant information in separate, disjointed information systems, even for international travel. Such systems are of particular interest to our research because trip planning typically involves locations previously unknown to travellers, or trips involve the use of complex travel infrastructure.  
Two such projects under the European Common Transport Area, LinkingAlps [4] and OJP4 Danube [5], seek to achieve integrated low-emission mobility and promote multimodality as a contribution to transport system optimisation.  
The LinkingAlps project focuses on the Alpine region, where remote areas often lack infrastructure and are poorly connected to public transport. By harmonising existing regional solutions and introducing innovative approaches based on a decentralised, transnational travel planning system, the project seeks to create sustainable cross-border mobility. The main objective of the project is to promote the transition from private motorised transport to low-carbon mobility options in passenger transport.  
Another European regional project, OJP4 Danube, integrates cross-border and cross-organisational coordination mechanisms and improves the technical and organisational alignment of transport operators and travel information service providers in the Danube Region. The project focuses on sustainable transport modes for local and long-distance traffic. The integration and exchange of information on main railway corridors connected to regional and local networks, including waterways and bicycle paths that increase the accessibility of the network, are core concerns of the project.  
The provision of an efficient operational network based on open timetabling will enable the dynamic integration of information across borders and operators. Travellers will be able to receive trip information from a distributed multimodal cross-border travel-information service. An important part of this planning is managing transfers between modes. The lack of information about the facilities and specific requirements of travellers at stops can be considered an important barrier to efficient trip planning. Knowledge of the infrastructures involved and their physical characteristics is necessary for planning the walking components of the trip. For example, inaccessibility for wheelchairs can be an insurmountable obstacle. Therefore, detailed and reliable information about the buildings and other facilities that make up infrastructures such as stations is of paramount importance.  
Both aforementioned projects draw on European standards and specifications such as Transmodel [6], NetEx [7], and Open API for Journey Planning [8] as the basis for service integration and data exchange.