Today I spotted a train labelled “Sonderwagen” on the U3 line running towards the Hohemark in Oberursel.
It was not the normal type of train that is used on this line, and there were all sorts of people from the train company running around it as it stood in the Kupferhammer station.
I took a photo as it approached “Rosengärtchen”, where it did not stop but carried on up the line. Does anyone know what this was about?