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The Forgotten Code That Helps Road Trippers Understand US Interstate Highways

United States Road Trips News
by Olivia Harden Feb 28, 2022

Highways: We pretty much all have to use them. In the era of being able to rely on the GPS on your phone, it’s pretty simple to figure out where you need to go. Things were different before people always had a map in their pocket, though. And it turns out that the numbers and names of highways hold the key to understanding where you’re going. The Youtube account CGP Grey recently explained some of the simple (and not so simple) rules of the road created by the Interstate Highway System.

The first set of rules to know are those that guide the interstate majors. Interstate majors follow an east-to-west, north-to-south system. All major interstates that run east to the west end in zero, and the numbers are listed depending on how far north or south it is. For example, the I-90 is the most northern east-to-west interstate and runs from Seattle to Boston. In contrast, the most southern east-to-west interstate, I-10, runs from Jacksonville, Florida, to Santa Monica, California.

East-to-west interstates listed from north to south:

  • Seattle to Boston: I-90
  • San Francisco to Teaneck, New Jersey: I-80
  • Cove Fort, Utah, to Baltimore: I-70
  • Barstow, California, to Wilmington, North Carolina: I-40
  • Little Rock, Arkansas, to Fort Worth, Texas: I-30
  • Florence, South Carolina, to Kent, Texas: I-20
  • Jacksonville, Florida, to Santa Monica, California: I-10.

Looking at that list, you might notice that I-50 and I-60 don’t exist. There were already highways older than the interstate system like Route 50 and Route 66, so the code skips I-50 and I-60 to avoid confusion.

Similarly, the north-to-south interstates all end in the number five. The I-5 goes from San Diego to Blaine, Washington, and is the farthest west north-to-south interstate, whereas I-95 from Houlton, Maine, to Miami is the farthest east north-to-south interstate.

North-to-south interstates listed from west to east:

  • San Diego to Blaine, Washington: I-5
  • San Diego to Sweet Grass, Montana: I-15
  • Las Cruces, New Mexico, to Buffalo, Wyoming: I-25
  • Houston, Texas, to Dallas, Texas: I-45
  • Sault Ste. Marie, Michigan, to Hialeah, Florida: I-75
  • Petersburg, Virginia, to Montgomery, Alabama: I-85
  • Houlton, Maine, to Miami: I-95

Contrary to the name, interstate highways like the I-45 can connect within a state and not necessarily between multiple states (in which case it’s an intrastate highway). There are also many rules explaining interstate mediums and interstate minors, with some exceptions.

Memorize these rules for your next road trip to the country’s best roadside attractions, and the next time your phone dies, these tricks and trips could help get to your destination without stopping for a charger.

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