Mercedes-Benz O530 Citaro were introduced on routes 507 and 521 on June 2, 2002. These were the first articulated buses to run in service on a regular basis, as opposed to merely being part of a trial. Following temporary removals from service due to fires on board and other criticisms, it was decided to retire these buses earlier than originally planned. The last one operated on December 10, 2011. The buses have since been transferred to other parts of the UK and even to Malta.