>>1289503In 2014, they planned something along those lines. A new line was to be introduced. It was gonna run along the southern branch of existing line 1, but branch off at Adenauerplatz / Kunsthalle, taking a more direct surface route over Jahnplatz (that's the central light rail/bus hub).
Then it was gonna turn east and serve a huge area that currently only gets busses (pic related). It would have been awesome, BUT...
It wouldn't really have solved the problem of the overcrowded tunnel. It was planned as a low-floor line (all the present lines are high-floor). That means it would have needed whole new rolling stock incompatible with the rest of the system, and complicated stations all along the south side which could have been served by both high floor line 1 and low floor line 5 trains. There was a public vote in summer of 2014 and it lost with like 54% of votes against it.
Currently, I can't imagine a new surface trunk route in the inner city even being discussed before 2030. Apparently the city wants to get rid of most of the car traffic and improve biking infrastructure and public transport significantly until then. But it currently can't even be assed to introduce a low-emission zone, bikers are still being fucked over left and right, and a significant portion of the city is just multi-lane roads, parking lots and expressways.
