List of Interstate Highways
There are 70 primary Interstate Highways in the Interstate Highway System, a network of controlled-access freeways in the United States. They are assigned one- or two-digit route numbers, whereas their associated "auxiliary" Interstate Highways receive three-digit route numbers. Typically, odd-numbered Interstates run south-north, with lower numbers in the west and higher numbers in the east; even-numbered Interstates run west-east, with lower numbers in the south and higher numbers in the north. Highways whose route numbers are divisible by "5" usually represent major coast-to-coast or border-to-border routes (ex. I-10 travels from Santa Monica, California, to Jacksonville, Florida, traveling from the Pacific to Atlantic oceans). Additionally, auxiliary highways have their numbering system where a different number prefixes the number of its parent highway.
U.S. Route 40
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.