Interstate 80
I-80 is the Interstate Highway that most closely approximates the route of the historic Lincoln Highway, the first road across the United States. The highway roughly traces other historically significant travel routes in the Western United States: the Oregon Trail across Wyoming and Nebraska, the California Trail across most of Nevada and California, the first transcontinental airmail route, and except in the Great Salt Lake area, the entire route of the First Transcontinental Railroad. From near Chicago east to near Youngstown, Ohio, I-80 is a toll road, containing the majority of both the Indiana Toll Road and the Ohio Turnpike. I-80 runs concurrently with I-90 from near Portage, Indiana, to Elyria, Ohio. In Pennsylvania, I-80 is known as the Keystone Shortway, a non-tolled freeway that crosses rural north-central portions of the state on the way to New Jersey and New York City.
Decommissioned highway
Decommissioned highways are common in the United States. Even in the early years of the United States Highway System, some highways had short lives as US highways especially if they were themselves short routes, such as the early US 110 in Wisconsin. Extensions of US routes have implied the elimination of earlier designations; as US 6, which originally went no farther west than the Hudson River in New York was extended to Long Beach, California over routes that included an old Indiana State Route 6, most of an old US 32 between Chicago and Omaha, all of US 38 between Omaha and Denver, and an old California State Highway 7 mostly in the Mojave Desert. US 6 was itself pared back to Bishop, California in the Great Renumbering of California in 1964.