Berlin's buses are a very important form of public transportation, as they complement the light rail systems wherever they were removed (trams in the West) or remain incomplete. Due to the heavy loads and demands of narrow streets, Berlin is one of the few cities in Europe to use double-decker buses extensively - over 400 of the 1400 buses in operation in Berlin are double-deckers. A ride in a Berlin double-decker should be on the to-do list of every first-time visitor to Berlin. Unlike other world cities, you should not flag down buses at stops in Berlin, even if there are multiple routes serving the stop. Some drivers may consider it an insult to their professionalism. A frequent problem with buses, particularly busy lines during rush hour and especially in the West (where they have to cope with levels of patronage more common for light rail lines) is bunching. As many buses come every five minutes during busy times, the first bus will get most of the passengers, meaning the bus behind catches up, which means the second bus gets even less passengers catching up even more, until finally two or three buses come a minute apart or even at the same time and then no bus comes for 15 minutes despite a nominal 5 minute headway. BVG are rather self-deprecating about the issue but aside from building new tram lines there is very little that can be done about it. Boarding fast and getting away from the door area is the best you can do to mitigate the issue.