ghost stations. maps in the transfer station were unique: They depicted all the Western lines, but not the , and showed the city divided into "" ("Berlin, capital of the German Democratic Republic") and "", the official terminology used by East Germany. The situation was less than ideal. The lines were a vital part of the West Berlin transit network, but because part of the route of some of the lines lay in East Berlin territory, it was difficult for Western support staff to perform maintenance work on the tracks and tunnels. If a train on a West Berlin line broke down in East Berlin territory, then passengers had to wait for Eastern border police to appear and escort them out. The East German government occasionally hinted that it might someday block access to the tunnels at the border and run its own service on the East Berlin sections of these lines. However, this awkward status quo persisted for the entire 28-year period of the division of Berlin. At the closed stations, barbed wire fences were installed to prevent any would-be escapees from East Berlin from accessing the track bed, and the electrically live third rail served as an additional and potentially lethal deterrent. An alarm was triggered if anyone breached one of the barriers. As for the entrances, the signage was removed, walkways were walled up and stairways were sealed with concrete slabs. Police stations were built into the windowed platform service booths, from which the whole platform area could be monitored. A wide white line on the wall marked the exact location of the border. Later, gates were installed at some stations that could be rolled into place at night while the guards were off-duty. Guard posts at other stations were staffed continuously, creating additional employment positions with the transport police. In the platform area, the guards always worked in pairs, and care was taken in their assignment to assure that there would be no personal ties between them. In addition, superior officers could conduct surprise inspections at any time, thus, maintaining maximum security. Other stations were secured by the East German border guards. Particular stations station, though served by Western lines and located in East Berlin territory, was not a . Instead, it served as a transfer point between U6 and several lines. Western passengers could walk from one platform to another without ever leaving the station