In the first part of my thesis I described in general the design documentation for construction and maintenance of railway lines in Slovenia. In the second part I wrote more in detail about design documentation for maintenance works to the public interest. I introduced the basics for making the design documentation, its contents and part of the design documentation on a specific project. I scooped and defined the terms, which are used in the context of the maintenance work of railway lines and using different schemes described how these terms have changed through the years in connection with different laws and regultions. I also pointed out some of the problems, which can appear because of different interpretations of these terms in Slovenian and European regulations.