S 21 Berlin (City Train Berlin), 3rd construction section
![drone flight over the planned line of the 3rd construction section of S21 © Al-Survey](/typo3temp/assets/_processed_/8/4/csm_Bild_1_ccceb5b519.png)
![track surveying for the design of the 3rd section © DB Netz AG](/typo3temp/assets/_processed_/9/6/csm_Bild_2_5d3d67f7ad.jpg)
![network survey for design of the 3rd section © DB Netz AG](/typo3temp/assets/_processed_/7/f/csm_Bild_3_a10b1817fe.jpg)
![overall as-built model](/typo3temp/assets/_processed_/c/5/csm_01_Bestandsmodell-Gesamt--210226_c15fe99c43.jpg)
![as-build model southern direction](/typo3temp/assets/_processed_/e/2/csm_03_Bestandsmodell-Ri-Sueden--210226_827bc5b4b5.png)
![as-built model northern direction](/typo3temp/assets/_processed_/5/2/csm_04_Bestandsmodell-Ri-Norden--210226_ab5675fe34.jpg)
![as-built model northern direction](/typo3temp/assets/_processed_/8/7/csm_04_Bestandsmodell-Ri-Norden2--210226_7017ac0f53.png)
Regional train line S 21 creates a second north-south line of Berlin’s regional trains in the city centre. The new train line will connect the quarter Wedding to train station Südkreuz via Central Station and thus integrate the Central Station into the regional train ring. In a joint venture with Amberg Engineering AG, SSF Ingenieure is charged with the mentioned services in the third section, a 2.1-km long, double-tracked tunnel-bridge line between stations Potsdamer Platz and Yorckstraße as well as Yorckstraße/Großgörschenstraße.After leaving the underground station Potsdamer Platz, the alignment runs downtown crossing the triangular junction until it connects to the existing line at Yorckstraße, branching off into two lines. In the area of the triangular junction, a new station is built maintaining the existing traffic structures and connected to an underground station, stations Yorckstraße and Yorckstraße/Großgörschenstraße are expanded and renewed.