Just a few meters west of the Schwamendinger Place tramway station, there is an x-shaped rail piece on which the tramcars change from right-hand travel on the overground lines to left-hand travel in the tunnel, which they enter soon after crossing.
The reason for this railpiece, which seems at first glance to be unnecessary - and a possible source for collisions - is that the tunnel was originally planned as a subway tunnel, in which stations would feature a single platform in the middle of the tracks.
In 1973, however, plans for a subway were canceled by popular vote; later it was decided that the already built tunnel would be reused for tramcars. As all of these cars are constructed with doors on the right side, the only way to run them in the tunnel is to use the left track, otherwise, passengers would not be able to enter or leave the cars.
On the other end of the tunnel, the tramcars switch back to their original tracks on different levels, making for a less remarkable - and apparently less dangerous - crossing point.