text: The  integrated Mannheim/Ludwigshafen tramway network also extends to Heidelberg. It is operated by RNV, a company that is wholly owned by the three cities mentioned and a couple of municipalities in the Palatinate. RNV is the result of a merger on 1 October 2009 between the region's five former municipal transportation companies. Interurban trams are operated by RNV on a triangular route between Mannheim, Heidelberg, and Weinheim that was originally established by the Upper Rhine Railway Company (Oberrheinische Eisenbahn, OEG), and the company also operates interurban trams between Bad Dürkheim, Ludwigshafen, and Mannheim. In the 1970s a proposal to build a U-Bahn out of the Mannheim and Ludwigshafen tramways was begun, but only small sections were built due to lack of funds. The only underground station in Mannheim is the Haltestelle Dalbergstraße. U-Bahn planning now has stopped. All public transport is offered at uniform prices set by the Verkehrsverbund Rhein-Neckar (Rhine-Neckar Transport Union, VRN).
  Block numbering and computer mapping
  The city centre uses an addressing system that is unique within Germany. Rather than street names and numbers, each block is given a code and a number is given to each building: C3, 17 is block C3, building 17. The practice dates back centuries and is a result of the original use of the city centre as a fort, with the fort's internal system being adopted when it became public streets. The streets themselves are unnamed. The codes are laid out in a simple progressive pattern: C3 is between C2 and C4 in one direction and B3 and D3 in the other. However, those not used to the system will often become lost. A street named Breite Straße goes through the middle of the blocks from south to north, with blocks A-K on the west side of the street and L-U on the east, with each row going 1 to at most 7 based on distance from this road. House numbers begin on the south corner nearest Breite Straße and go counterclockwise for A-K and clockwise for L-U.