During the planning phase of the Cologne–Frankfurt high-speed line in the 1980s and early 1990s, a proposal to build a new line via Bonn station was controversial. This proposed a tunnel under the city, which would begin on the northern outskirts of Bonn and run through a deep level station 35 m below the main station. After crossing under the government district, the Rhine and the Siebengebirge hills to reach the line route that favoured by the Deutsche Bundesbahn to run via Limburg an der Lahn to Frankfurt. The additional cost of this option was estimated at about half a billion Euros. In addition, a route via Bonn-Beuel and Aegidienberg through a 14 km long tunnel was also considered. Today, Bonn Hauptbahnhof is connected indirectly to the high-speed line, by tram line 66 of the Bonn Stadtbahn to Siegburg/Bonn station. Despite Intercity-Express services running through Siegburg/Bonn rather than Bonn, Bonn Hauptbahnhof is still a major stop for long-distance traffic.