@inproceedings{BorndoerferLiebchen2008, author = {Ralf Bornd{\"o}rfer and Christian Liebchen}, title = {When Periodic Timetables are Suboptimal}, booktitle = {Operations Research Proceedings 2007}, editor = {J{\"o}rg Kalcsics and Stefan Nickel}, pages = {449 -- 454}, year = {2008}, }