🚛 🚗 The Interstate's Forgotten Code 🚗 🚛

The interstate highway shields hide within them long forgotten knowledge. As our great ancestors could navigate by the signs in the sky before the creation of the compass, so too before GPS could they navigate by these signs. Come with me and learn how to navigate the constellations created across a continent by the First.

Are the Interstate Majors, beginning with I-90 from Seattle to Boston, the longest and northern-ist of all the I's? Then the southern-ist, Jacksonville, Florida, to Santa Monica, California: I-10. Interstate Majors that run east-west are double digits ending in zero. The bigger the northern-er.

So filling in the rest, the next northern-est is San Francisco, California, to Teaneck, New Jersey: I-80. And the next southern-est is Florence, South Carolina, to Kent, Texas: I-20. Then Cove Fort, Utah, to Baltimore, Maryland: I-70, and Little Rock, Arkansas, to Fort Worth, Texas: I-30.

Okay, so that one is the most minor of the Majors, and it doesn't quite fit as well with the rest with its diagonality. But I'm confident it’s the lone exception and not foreshadowing. Next is Barstow, California, to Wilmington, North Carolina: I-40. Then, I-50 and I-60, which don't exist.

See, there are older highways than the Interstate System, slower other ways, not built to the Interstate's Book of Exalted Construction Codes. These are called US Highways or US Routes, the most famous of which is Route 66. And these use the United States Numbered Highway System which put the old US Route 50 and 60 right in the middle.

The Department of Transportation knew that only the most devout roadway anoraks would be attune to the difference between Interstates and Routes, and normals would simply look at the number. To simplify everyone’s life, DOT skipped Interstates 50 and 60, to avoid minds getting muddled in the middle of 'Merica. That's the East-West Interstates Majors covered.

Now on to North-South. The longest of which is Maine to Miami, Florida: I-95. Which, like all majors, no exceptions surely, are double digits, but ending in five now to indicate verticality. On the opposite coast, San Diego, California, to Blaine, Washington is I-5.

Okay, so already that's not double digits, but maybe officially it has a leading zero, but just not on the sign, right, Department of Transportation? No? Okay. Well, then I-5 has a leading zero in our hearts. The rest of the North-South Interstate Majors are Petersburg, Virginia, to Montgomery, Alabama: I-85, a bit of a sister route to I-30.

San Diego, California, to Sweet Grass, Montana: I-15. Sault Ste. Marie, Michigan, to Hialeah, Florida: I-75. Las Cruces, New Mexico, to Buffalo, Wyoming: I-25. Then I-45 from Houston, Texas, to... Dallas, Texas.

Contrary to popular belief, interstates don't have to be interstate interstates; they can be intrastate interstates. The obvious examples are Hawaii and Alaska, which have intrastate interstates, but also Puerto Rico, which has an I— I mean, I guess technically it’s an... Anyway, these three, being physically disconnected from the rest of the network, use a different numbering system with letters.

But back on the continent, there are in fact way more intrastate interstates than interstate interstates. Most are the Interstate Minors we will get to, but I-45 is notable for being the only Interstate Major that's intrastate. Finishing up the North-South Majors, it’s Texas again, in Laredo, to Duluth, Minnesota: I-35.

Then Chicago, Illinois, to LaPlace, Louisiana: I-55. And finally hop over to Mobile, Alabama, up to Gary, Indiana on I-65. Together, the Interstate Majors constellation with its shining numbers lets you navigate the nation. The lower the numbers, the more South and West you are. The higher, North and East.

If it ends in zero, you’re traveling horizontally. And if it ends in five, vertically. Very satisfying. Now there are scores of lesser connecting constellations as well. These are Interstate Minors and use three digits to communicate their navigational secrets. Interstate Minors diverge from a Major and have their last two digits match the Major from whence they came.

Then, if the first digit is even, it means the Interstate Minor will eventually connect back to its parent Major. For example, as I-70 crosses the nation, I-670 diverts in Kansas City, Missouri, but eventually circles back to connect to I-70 in Kansas City, Kansas. Even-numbered Minors are often called Bypasses when they bypass something, or Beltways when they encircle something.

An Interstate Minor that starts with an odd number warns that it will not connect back to its parent. This is called a Spur. Example: as I-90 goes past Buffalo, I-190 diverges and the odd digit lets you know you won’t be coming back. Instead, plunging one way into the wilds of Canada. Nice!

Though sometimes a Spur won’t just go nowhere. It will instead connect back to another Interstate Major. In this case, which of the double digits are used as the base of the triple? And the answer is... there isn't a consistent answer; it's up to the states.

So that's Interstate Majors and Minors, but there's also Interstate Mediums. Like I-64 from Wentzville, Missouri, to Chesapeake, Virginia. And I-29 from Kansas City, Missouri, to Pembina, North Dakota. The Interstate Mediums follow the same numbering pattern as the Majors, all two digits, if we keep those leading zeros in our hearts.

Evens: East-West. Odds: North-South. All in order too, except for I-99, which is so annoying. DOT, why did you do this?! What?! Congress specifically picked 99 out of order for this highway? So Congress is the only one who can fix it? Ughhhhhhhh.

Well, let's just try to ignore that and move on. The Interstate Majors are all uniquely numbered, but not so with the Mediums. There's an I-76 from Big Springs, Nebraska, to Denver, Colorado. And another I-76 from Bellmar, New Jersey, to Akron, Ohio. Sandwiched between the Majors I-90 and I-80 are duplicate Medium I-84s, I-86s, I-87s, and I-88s.

The rule is that as long as the duplicates are far enough away to avoid muddling minds, it's fine. There are also loads of duplicate Interstate Minors, which there have to be if you think about it. Take I-95, which crosses fifteen densely populated states. To only have nine options for spurs and bypasses would be rather limiting.

In fact, just Maryland alone has an I-195, 295, 395, 495, 595, 695, 795, 895, and… really? Ughh, so close. DOT, you've got to build an I-995 in Maryland just to complete the set for me. Please! So that's the system. But as we've already seen with Interstate Mediums, anything built over decades is going to acquire exceptions.

And, taking a little detour to my home interstate I-495 aka the Long Island Expressway aka the L.I.E. Don't dare call it "the LIE" or locals will laugh at you. This is the spinal spur of the Long Island fish, never connecting back to its parent I-95 because Long Island is... an island.

But as a one-way spur, it should start with an odd digit, not an even. And it really should be a two-digit Interstate Medium because it technically doesn't connect to I-95 at all, rather just dropping you off in midtown Manhattan, with an... I guess the L.I.E. is a lie after all.

A worse exception on the other coast in San Francisco is Interstate 238. Which the number tells you should be a bypass off of I-38. But no, I-38 doesn't exist. I-238 is a one-way spur connecting two other Interstate Minors: I-580 and I-880. So, I don’t even know what’s going on here.

There's also some weirdly one-off numbering such as: I-35, which splits into I-35 East and I-35 West to reach Fort Worth and Dallas before re-joining, and pulls the same trick up North, dividing in twain East-West branches again to hit the Twin Cities. Why wasn’t just one of the branches on each end picked to be the bypass so that the system could be consistent?

Was it because the cities didn’t want to be the one considered “bypassed?” Ughh. That’s totally the reason, isn’t it? The weirdest one-off is the nice I-69. Which splits itself into I-69 East, I-69 West, and I-69C. Okay, you do you, I-69. At least you have a sign, unlike, back in New York, with America's smallest Interstate 878 at just under a mile.

Which apparently doesn't deserve a sign. So the interstate anoraks can never complete their selfie collection. Okay, that's enough exceptions. I could do this all day. (I already cut so many from the script you wouldn't believe it.)

Back to the big, beautiful constructed constellation and its lost wayfinding ways, now revealed, so that as your ancestors before you navigated by the sky, you too can go on an American road trip navigating by the interstate numbers alone.

[twinkling, ethereal music plays softly] Well, after you memorize all the exceptions. [music fades slowly] I mean, practically, you should still just use your GPS. It's very reliable and it also lets you know the traffic.