Part of this line between Mellingen and Gexi junction (near Hendschiken) together with the AS line between Gexi junction and Rupperswil was incorporated into the current main line between Zürich and Olten when a shorter and straighter line between Killwangen-Spreitenbach and Rupperswil was opened through the 4929 meters long Heitersberg Tunnel on 22 May 1975.