The new Berlin S-Bahn route will run in the south from Südkreuz via the Main Station and Potsdamer Platz to Wedding and Westhafen in the north. After delays and delays, the most recent news is, it will take at least 15 years to build reports Der Tagesspiegel. Deutsche Bahn gives 2037 as the planned completion date.

The 7.2 km long route (Nordring-Yorckstrasse/Yorckstrasse [Großgörschenstrasse]) will cost almost 1 Billion euros. It will be implemented in 3 construction phases "BA"s with a possible extension to phase "BA 3b (Cherusker curve)".  Construction already started in 2011 (1st BA, earlier measures). The route will go through tunnels, bridges and at ground level rails. 

According to project plan, following are the phases:

BA1 - Construction phase 1: Connection Nordring - Berlin Hauptbahnhof

• Bridge trains in the area of ​​the Nordring connection as well as free routes in the direction of the main station Two-track tunnel areas with connection to Berlin Central Station
• New construction of the Berlin Hauptbahnhof traffic station
• Currently under construction

BA2 - Construction phase 2: Central Station – Potsdamer Platz

• New construction with partly two single-track tunnel tubes and connection to the existing tunnel
• North-south S-Bahn in the "Heuboden" area as well as the tunnel 1. BA of the S 21 under construction
• New construction of the technical line equipment
• Currently in draft planning

BA3 - Construction phase 3a: Potsdamer Platz - Yorckstraße / Yorckstraße (Grossgörschenstrasse)

• New construction of a double-track line in a tunnel location and as a bridge
• New parking facility at Gleisdreieck
• New construction of a traffic station in the Gleisdreieck area and its connection to the Urban development measure “Urbane Mitte Berlin” as well as basic renewal/expansion of the Traffic stations Yorckstraße and Yorckstraße (Großgörschenstraße)

BA3b - Construction phase 3b: Julius-Leber-Bridge - Südring (northeast curve)

• Planning postponed until further notice by the state of Berlin

The whole project information, with the high-level project plan, good quality visuals at the project (PDF) of Deutsche Bahn site:https://bauprojekte.deutschebahn.com/media/projects/7221/docs/PR_digitale_informationsveranstaltung_20220121.pdf

map: Deutsche Bahn Berlin S-Bahn S21 (Deutsche Bahn Berlin S-Bahn S21 youtube project video)