The existing arrangements faced competition from the development of automobile traffic, and the federal government was anxious to transform Bonn from a provincial town to a modern capital.

However, the KBE went into financial decline at the end of the decade and survived only with the support of the North Rhine-Westphalia government; in this environment expansion was impossible.

The only completely new section is the connection over the Südbrücke (South Bridge), which is used by the 66 and 68 lines on the southbound journey from Bonn Hauptbahnhof to Ramersdorf and Bad Honnef.

The majority of the route runs through a tunnel between Hauptbahnhof and Heussallee/Museumsmeile, constructed in 1975, replacing the BGM-operated tram tracks which ran above-ground along the Adenauerallee and down to Bad Godesberg.

The Bonn Stadtbahn covers 95.84 kilometres (59.55 mi) of route[1] and is composed of six lines all together, of which four operate regularly and two only during peak hours: