U.S. Route 40 (US 40) is an east–west United States Highway. As with most routes whose numbers end in a zero, US 40 once traversed the entire United States. It is one of the original 1926 U.S. Highways, and its first termini were San Francisco, California, and 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 at its western end.