Active railway lines with no trains. Yes, there are many of these in border areas! Either railway lines that are legally active, but have no trains at all running on them. Or, more commonly, tracks that have freight trains but no passenger trains. In a few cases, missing electrification of the lines at the cross border section adds a further complication.
If the infrastructure is in place, it should be a comparatively simple task to (re-)start passenger operations!
Please use the links in the menu for details of the individual borders.