Berlin North–South mainline

In 1882 the Stadtbahn was opened crossing central Berlin east to west. Plans since the beginning of the 20th century for a similar line from north to south for a long time came to nothing. The North-South tunnel built in the 1930s through the city centre only serves the S-Bahn.

After the reunification of Germany and Berlin in 1990, a north-south line for mainline trains through Berlin was discussed. The use of the Stadtbahn for mainline trains meant that many connections required a devious route and in addition the limit of its capacity was expected to be reached soon. Among the various options discussed and then adopted was the so-called mushroom concept (German: Pilzkonzept), which provided for a partially underground north-south route, which crossed the Stadtbahn at the Hauptbahnhof.

In April 1992, the mushroom concept was added to the Federal Transport Infrastructure Plan.[2] Its core would be a new 8-kilometre (5.0 mi)-long route through the city with a 3.5 km (2.2 mi) long tunnel.[3] Construction began on 13 October 1995.[4] In 2001, reconstruction began on the Papestraße S-Bahn station, creating the new Südkreuz station. In 2002, construction began on the southern section of the above ground line, originally planned to be opened in 2002.[5] After a series of delays, including flooding in 1997, the track, tunnels and Hauptbahnhof was finally inaugurated on 27 May 2006 and put into scheduled operation a day later.

Compared to the original schedule, the project scope has been reduced. A link to the trunk line towards Potsdam was not built. Instead only some structural preparations for a connection in the southern part of the tunnel were built. Similarly, the connection of the Dresden Railway to Berlin has still not been rebuilt. The Südkreuz station was originally opened with only two of its three long-distance platforms. The third platform was not connected to the network until late 2007 to provide additional capacity during traffic disruptions.

The route is open only for passenger trains; freight is not allowed. The terms of access require the use of a retention toilet system and the use of eddy current brakes is not permitted on the line. Diesel trains can only run on the line in an emergency (such as towing a wrecked train).

The train service has not changed substantially since the opening of the line in 2006, apart from the fact that the Hamburg–Leipzig–Munich Intercity-Express (ICE) line has since 2008 usually divided in Berlin, so that instead of a continuous service there has been a Hamburg–Südkreuz train and a Gesundbrunnen–Munich train on the line.

The following table shows the services of long-distance and regional lines, which run on the north-south main line (as of 2015): services run from Spandau on the Lehrter line to the meeting of the two lines at the northern end of the Hauptbahnhof and from Gesundbrunnen on the Wedding branch to the north-south mainline. All trains go via Berlin Hauptbahnhof; almost all continue to Südkreuz.

In addition, there are a number of less regular services. The night train runs between Paris and Berlin-Südkreuz. A number of additional Intercity (IC) trains run at the weekend towards Hanover and Cologne as well as to Frankfurt am Main use the route. Most of the ICE and IC trains run on these routes, on the other hand, use the Stadtbahn. Deutsche Bahn has made relatively little use of the capacity of the four-track line. Initially it was planned to run ICE trains from Frankfurt to Südkreuz. Those plans came to nothing, however, because there were no equivalent for the maintenance of trains to the Rummelsburg yard that was available for trains on the Stadtbahn that would not require additional expenditure.

Given the lack of an S-Bahn connection to Berlin Hauptbahnhof in the north-south direction, there was a proposal to use the spare capacity of the north-south mainline for the S-Bahn. However, it has now been agreed to build a new S-Bahn line from the northern Ring Bahn to Hauptbahnhof, extending it eventually to Potsdamer Platz.