Public transport plans are a planning tool which helps to assure the provision of adequate public transport infrastructure and services, economic operations as well as harmonized tariffs and timetables. They set the foundation for the work of transit alliances and other transport planning authorities. Read more here (German language only):
Publikationen | Verkehrsverbund Rhein-Ruhr (vrr.de)
GIZ has published an overview of how to finance sustainable public transport regarding international as well as German case studies:
2013_Diaz_Bongardt_FinancingSustainableUrbanTransport.pdf (changing-transport.org)