The head of Germany\'s rail operator has apologised for chaos that hit a major train hub, leaving commuters fuming. Staff shortages in the western city of Mainz caused hours-long delays for thousands of commuters and holiday-makers, and turned into a campaign issue six weeks before a general election set for September 22. Opposition parties have sought to make political capital from the chaos, variously blaming a decade-old free-market shift for the problems or arguing it hasn\'t gone far enough. In press interviews to be published Sunday, Ruediger Grube, who interrupted a holiday abroad to tackle the problems, said Deutsche Bahn (DB) had \"covered itself in ridicule\". \"I sincerely apologise for the problems that were caused,\" Gruber told the German weekly Welt am Sonntag. \"What happened in Mainz should not happen. Unfortunately it did happen. Now we must work hard to ensure it cannot happen again.\"