Passenger information systems on London Underground Limited rolling stock

London Underground Limited is the oldest and one of the largest metros in the world and as such it has been carrying a very large number of passengers for a very long time. Indeed the Northern line, parts of which were opened in 1890s, has just celebrated its centenary. When considering these facts about this heavily loaded and complex service, it becomes obvious that for reasons of passenger comfort and safety, the Underground needs to have user-friendly passenger information systems to prevent unnecessary confusion and congestion. The company therefore utilises a number of such systems, both audio and visual, throughout the Underground, although the authors concentrate only on those passenger information systems to be found in use on-board air rolling stock