The design called for five levels. The highest level, on a bridge 10 metres above street level, was to have platforms for both long-distance and S-Bahn trains on the existing Stadbahn. The lowest level, 15 metres underground, was to have platforms served by new tunnels to Potsdamer Platz under the Spree and the Tiergarten, forming a new north–south line running to the northern part of the S-Bahn ring around central Berlin. Platforms for the planned extension to U-Bahn line 5 were also included.