沙夫豪森州
Originally, the Black Forest line was intended as a feeder line to the Swiss Gotthardbahn, across the first German-Swiss border crossing near Waldshut and Koblenz. Geological issues in the Wutach Valley prevented taking a path in a southerly direction from Donaueschingen, and trains took a lengthy detour around the Swiss Canton of Schaffhausen to reach Singen, near Lake Constance, which was the ultimate destination.