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I drove my truck cross country twice before I realized the interstate highways are numbered with a basic sequential system. My “duh” moment came after I spent four days of my life on I-80, looked at a map, and thought: “I-90 is north of me, and I-70 is south…I wonder if they are all numbered this way?” But few modern drivers even carry a paper map, and many have yet to realize how well-organized the interstate numbering system is. How do I know? Because a map of the USA highway names is going viral on social media.

How are the interstate highways named?

The major interstate highways in the U.S.A. carry double-digit numbers and end in a five if they go north-south or a zero if they run east-west. They are named in ascending order, beginning in the west and going east or beginning in the south and going north.

Map of the major routes in the US National Interstate Highway system.
U.S. Interstate Highways | CGP Grey via YouTube

If the above picture of the major interstate highways is confusing, have no fear, simpler maps are coming. Let’s start with the east-west highways. The northernmost cross-country highway, running from Seattle to Boston, is I-90. The southernmost is I-10, stretching from Jacksonville, Florida, to Santa Monica, California. The highway connecting San Francisco, California, to Teaneck, New Jersey, is my beloved I-80. Both I-20 and I-30 “T” into I-10 before reaching the Pacific. I-70 begins in Baltimore, Maryland, and makes it to Cove Fort, Utah, before dead-ending.

So what about I-50 and I-60? While the government was planning the interstate highway system (established in 1956), two-lane U.S. Highways/Routes were a popular way to travel. The Rolling Stones, for example, were still getting their kicks on Route 66. This old system included a popular US Route 50 and a US Route 60. The new system’s designers supposedly skipped I-50 and I-60 to avoid confusion. Here’s how the east-west interstates look:

Map of all the major east-west divided highways in the USA interstate system.
Major East-West Interstate Highways | CGP Grey via YouTube

What are the names of the north-south interstate highways?

The north-south interstate highway names are just as simple. I-95 runs from Houlton, Maine to Miami, Florida. I-85 starts in Montgomery, Alabama, but Ts into I-95 in Petersburg, Virginia.

I-75 stretches all the way from Sult Ste. Marie, in Michigan’s Upper Penninsula to Hialeah, Florida. It, confusingly, crosses over I-85 en route. I-65 begins in Gary, Indiana, and ends down in Mobile, Alabama. I-55 starts in Chicago and ends in LaPlace, Louisiana.

Map of all the major north-south divided highways in the USA interstate system.
Major North-South Interstate Highways | CGP Grey via YouTube

I-45 is the only major “interstate” contained in one state, beginning in Houston and ending in Dallas, Texas. That said, Hawaii, Alaska, and Puerto Rico all have minor interstate highways, the names of which begin with H, A, and PR, respectively.

Let’s get back on track with our north-south interstate majors: interstate highway I-35 runs from Laredo, Texas, to Duluth, Minnesota. I-25 starts in Las Cruces, New Mexico, and ends in Buffalo, Wyoming. I-15 stretches from Sweet Grass, Montana, and ends in San Diego, California. I-5 starts in Blaine, Washington, and also ends in San Diego, California. I suppose it would technically be I-05, but the DOT is no MI6. Running along the Pacific Ocean is, of course, the famous Route 1. Its name fits the sequence, but it is not a divided interstate highway, just a U.S. Route (like Route 66, remember?).

Why are people surprised by the interstate highway numbers?

The saying “You can’t see the forest for the trees” means being so focused on the details that you can’t see the big picture. Here’s an example: A map of the USA’s interstate highway numbering system has been going viral on social media. Why? Because countless Americans who drive a U.S. interstate regularly had no clue they were all named using a simple, sequential system.

But if you ever find yourself without phone service while driving a major interstate highway, the road’s name can tell you a lot. The lower the highway’s number, the further south/west you are. The higher the number, the further north/west you are. If the road’s number ends in zero, you’re traveling east-west; if it ends in five, you’re traveling north/south.

Because navigational GPSs and cellphone navigation have been common for over a decade, knowledge of the interstate highway system naming conventions may skip a generation. YouTuber CGP Grey gently pokes fun at this generational difference with the video: “The Interstate’s Forgotten Code,” comparing navigating by road names alone to navigating by the stars.

Another confusing factor is the number of spur interstates with their three-digit names. Luckily, these names follow their own simple conventions.

Next, find out which interstate highway has the fastest speed limit, or learn about spur highway naming conventions in CGP’s video, embedded below: