The State Street subway opened on October 17, 1943, providing two new tracks bypassing the Loop tracks and the portion of the North and South Side "L" lines not equipped with express tracks. By providing an express route free of the most restrictive curves on the Chicago "L" and shorter than the old line it supplemented, the subway reduced running time by as much as eleven minutes for a one-way trip. The route was placed in operation on October 17, 1943, for a portion of the through north–south trains, although other trains continued to use the "L" both on through trips and on services circling the Loop and returning to the point of origin.