on most of the main line north of Kensington/115th Street station, with local trains running in the center two tracks, and express trains on the outer two tracks. Outside the United States the Chūō Main Line is an example of a modern, heavily utilized urban quadruple track railway. Quadruple track is used in rapid transit systems as well: throughout the New York City Subway, the Chicago "L"'s North Side Main Line, and SEPTA's Broad Street Line in the United States, and on the London Underground in the United Kingdom. Oddities Non-parallel double track The two tracks of a double-track railway do not have to follow the same alignment if the terrain is difficult. At Frampton, New South Wales, Australia, the uphill track follows something of a horseshoe curve at 1 in 75 gradient, while the shorter downhill track follows the original single track at 1 in 40 grades. A similar arrangement to Frampton could not be adopted between Rydal and Sodwalls on the Main Western railway line because the 1 in 75 uphill track is on the wrong side of the 1 in 40 downhill track, so both tracks follow the 1 in 75 grade. Another example is at Gunning. Between Junee and Marinna, New South Wales, Australia the two tracks are at different levels, with the original southbound and downhill track following ground level with a steep gradient, while the newer northbound and uphill track has a gentler gradient at the cost of more cut and fill. At the Bethungra Spiral, Australia, the downhill track follows the original short and steep alignment, while the uphill track follows a longer, more easily graded alignment including a spiral. At Saunderton, England, what became the London-to-Birmingham main line of the Great Western Railway in 1909 was initially part of a single-track branch line from Maidenhead. Down trains follow the route of the old branch line, while up trains follow a more gently graded new construction through a tunnel. This scheme avoided the cost of a new double-track tunnel. Directional running Directional running is two separate lines being operationally combined to act as a double-track line by converting each line to unidirectional traffic. An example is in central Nevada, where the Western Pacific and Southern Pacific Railroads, longtime rivals who each built and operated tracks between northern California and Utah, agreed to share their lines between meeting points near Winnemucca and Wells, a