In 1866 the B&O began constructing the Metropolitan Branch west out of Washington, which was completed in 1873 after years of erratic effort. Before this line was laid, rail traffic west of Washington had to travel first to Relay or Baltimore before joining the main line. The line cut a more or less straight line from Washington to Point of Rocks, Maryland, with many grades and large bridges. Upon the opening of this line, through passenger traffic was rerouted through Washington, and the Old Main Line from Point of Rocks to Relay was reduced to secondary status as far as passenger service was concerned. The Washington to Gaithersburg section of the Met Branch was double-tracked during 1886–1893. Rebuilding in the early 20th century and complete double tracking of the branch by 1928 increased capacity; the "branches" became the "de facto" mainline, though the Old Main Line was retained as a relief route.