@techreport{BorndoerferErolGraffagninoetal.2010, author = {Ralf Bornd{\"o}rfer and Berkan Erol and Thomas Graffagnino and Thomas Schlechte and Elmar Swarat}, title = {Aggregation Methods for Railway Networks}, institution = {ZIB}, address = {Takustr. 7, 14195 Berlin}, number = {10-23}, language = {eng}, year = {2010} }