U.S. Route 40 or U.S. Highway 40 (US 40), also known as the Main Street of America, is a major east–west United States Highway traveling across the United States from the Mountain States to the Mid-Atlantic States. As with most routes whose numbers end in a zero, US 40 once traversed the entire United States. It is one of the first U.S. Highways created in 1926 and its original termini were in San Francisco, California. Its eastern terminus is currently at Albany Avenue and Ventnor Avenue in Atlantic City, New Jersey. In the western United States, US 40 was functionally replaced by Interstate 80 (I-80), resulting in the route being truncated multiple times. US 40 currently ends at a junction with I-80/US 189 in Silver Summit, Utah, just outside of Salt Lake City.
Starting at its western terminus in Utah, US 40 crosses a total of 12 states, including Colorado, Kansas, Missouri, Illinois, Indiana, Ohio, West Virginia, Pennsylvania, Maryland, Delaware, and New Jersey. Three former and four current state capitals lie along the route. For much of its route, US 40 runs parallel to or concurrently with several major Interstate Highways: Interstate 70 from Colorado to Washington, Pennsylvania; and again from Hancock, Maryland to Baltimore, Maryland; Interstate 64 in parts of Missouri and Illinois; Interstate 68 along the Maryland Panhandle; and Interstate 95 from Baltimore to New Castle, Delaware. US 40 also passes through major cities including Denver, Kansas City, St. Louis, Indianapolis, Columbus, Baltimore, and Wilmington.
The route was built on top of several older highways, most notably the National Road and the Victory Highway. The National Road was created in 1806 by an act of Congress to serve as the first federally funded highway construction project. When completed it connected Cumberland, Maryland, with Vandalia, Illinois. The Victory Highway was designated as a memorial to World War I veterans and ran from Kansas City, Missouri to San Francisco, California. Other important roads that have become part of US 40 include Zane's Trace in Ohio, Braddock Road in Maryland and Pennsylvania, the Black Horse Pike in New Jersey, part of the Oregon Trail in Kansas, and the Lincoln Highway throughout most of California.
