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 trains using a third rail would travel.
In 1973, however, these plans were canceled and it was decided the tunnel would be used 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 rail, 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 decidedly less dangerous - crossing point.