Is there any rhyme or reason to how U.S. interstate highways are numbered?
Yes, there is. But first you need to know a little about the interstate highway system. Known officially as the Dwight D. Eisenhower System of Interstate and Defense Highways, this massive federal road-building project began in the late 1930s. But it wasn’t until 1952 that Congress authorized spending and construction began. In 1956, uniform construction standards were adopted, governing such things as access, speeds, number of lanes, width of lanes and width of shoulders. Standards were also established for numbering the routes: • Routes with odd numbers run north-south. • Routes with even numbers run east-west. • For north-south routes, the lowest numbers are in the west. • For east-west routes, the lowest numbers are in the south. So, I-5 runs north-south along the west coast, while I-10 runs east-west in the south. The major transcontinental routes are: When an interstate hits a major urban area, beltways around the city carry a three-digit number. These routes are designated with
