Numbering the Highway System

Updated February 21, 2017 | Factmonster Staff

Knowing your numbers helps you know which direction you are going on U.S. highways. Here's how the highway systems are numbered.

Interstate Highways

Three highways run from coast to coast: I-10, I-80, and I-90. Seven highways run from border to border: I-5, I-15, I-35, I-55, I-65, I-75, and I-95.

  • The interstate system totals 46,300 miles. All interstate highways are marked by blue signs with red tops.
  • The north-south highways have odd numbers with 1 or 2 digits, usually including a 5. The lowest numbers are on the West Coast and increase as they move east. For example, I-5 is on the West Coast, I-95 on the East Coast.
  • The east-west highways have even numbers with 1 or 2 digits. The lowest numbers are in the South and increase as they go north. For example, I-4 runs through Florida; I-96 is the northernmost route.
  • An interstate highway with 3 digits is a connector or offshoot of a main route.

U.S. Routes

  • U.S. routes are posted in black letters on white signs.
  • The north-south routes have odd numbers, with 1 to 3 digits. These numbers increase from east to west (just the opposite of the interstate system). For example, U.S. 1 runs along the East Coast; U.S. 101 runs along the West Coast.
  • The east-west routes have even numbers, with 1 to 3 digits. The lowest numbers are in the North and increase moving south (just the opposite of the interstates). For example, U.S. 2 runs along the Canadian border; U.S. 90 runs through Texas.

For the distance between many U.S. cities, see Road Mileages Between U.S. Cities at

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