First there was the railway viaduct. Then there was a highway, with 2 lanes in each direction. It just fitted between the pillars.
When the highway had to be widened with 3 lanes in each direction, a big problem arose, because the distance between the pillars is too narrow.
To solve this, a bridge was built on which a part of the viaduct now rests and under which the vehicles can drive.
The viaduct is still used today by trains, but also by trams. I do not know the number of the tram. The purpose of the photo was this special viaduct from 1868 in combination with a modern tram.