Directional running is when two separate lines are operationally combined to act as a double-track line by converting each line to unidirectional traffic. An example of directional running occurs in central Nevada. 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 distance of approximately . Westbound trains from both companies used the Southern Pacific's Overland Route while eastbound trains used the Western Pacific's Feather River Route (now called the Central Corridor). Crossovers were constructed where the lines ran in close proximity to allow reverse movements. This was necessary as while for most of this run the tracks straddle opposite sides of the Humboldt River, at points the two tracks are several miles apart and some destinations and branch lines can only be accessed from one of the lines. There is a grade separated crossover of the two lines in the shared track area near Palisade, Nevada. This results in trains following right hand traffic in the eastern half of the shared track area, but left hand traffic in the western half. The Union Pacific Railroad has since acquired both of these lines, and continues to operate them as separate lines using directional running. Amtrak also runs the "California Zephyr" along these routes.