The Alexanderplatz, as shown in the opening sequence and at least in S02E06 (the same shot), is a digitally retouched version of the current Alexanderplatz. As visible in any old photograph and even a 1936 color documentary, before WW2 there would have been a green roundabout in the middle through which the tram tracks ran, and paved streets with cars around it.
This is also the reason why the tram shown in the shot uses an historically incorrect pantograph instead of a trolley pole.