The line crosses through the southern part of the French department of Haut-Rhin, serving the commune of Leymen.

[2][3] The line was extended another 5.6 kilometres (3.5 mi) to Flüh, on the border with Alsace (then part of the German Empire).

World War II and the German invasion of France led to the closure of the line a second time, between 1940 and 1945.

[6] In 1984, the line's electrification was converted to 600 V DC to permit interoperation with the rest of the Basel tram network.

Crossing back into Switzerland, it serves the municipalities of Bättwil, Witterswil, and Ettingen, and then turns north to follow the Birsig river.