The interstate highway shields hide long forgotten knowledge, just like our ancestors used to navigate by the stars before the creation of the compass and GPS. Let’s take a look at the Interstate Majors, starting with I-90, the longest and northern-most, which runs from Seattle to Boston. The southern-most is I-10, which goes from Jacksonville, Florida to Santa Monica, California. All east-west Interstate Majors end in zero. So following this pattern, I-80 runs from San Francisco, California to Teaneck, New Jersey, and I-20 goes from Florence, South Carolina to Kent, Texas. I-70 is slightly different, as it runs diagonally from Cove Fort, Utah to Baltimore, Maryland, and I-30 from Little Rock, Arkansas to Fort Worth, Texas. I-40 follows, running from Barstow, California to Wilmington, North Carolina. I-50 and I-60 don’t exist, as they are part of the United States Numbered Highway System, which includes US Routes such as Route 66.
Moving on to the North-South Interstate Majors, the longest is I-95, which goes from Maine to Miami, Florida. I-5 is the opposite coast, running from San Diego, California to Blaine, Washington. I-85 follows, going from Petersburg, Virginia to Montgomery, Alabama. I-15 runs from San Diego, California to Sweet Grass, Montana, and I-75 from Sault Ste.Marie, Michigan to Hialeah, Florida. I-25 goes from Las Cruces, New Mexico to Buffalo, Wyoming, and I-45 from Houston, Texas to Dallas, Texas. Finally, I-35 runs from Laredo, Texas to Duluth, Minnesota, I-55 from Chicago, Illinois to LaPlace, Louisiana, and I-65 from Mobile, Alabama to Gary, Indiana.
The lower the numbers, the more South and West you are, and the higher, North and East. If it ends in zero, you’re traveling horizontally, and if it ends in five, vertically. There are also Interstate Minors which use three digits to communicate their navigational secrets. Hawaii, Alaska, and Puerto Rico use a different numbering system with letters, and I-45 is the only Interstate Major that’s intrastate. It goes from Port Huron, Michigan, to Indianapolis, Indiana.It’s part of a larger system of I-69s that will eventually connect all the way to the Mexican border.But for now, it’s a weirdly one-off number.
Interstate Minors diverge from a Major and have their last two digits match the Major from whence they came. If the first digit is even, it means the 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, it plunges one way into the wilds of Canada.
Sometimes a Spur won’t just go nowhere; it will instead connect back to another Interstate Major. In this case, the double digits are not necessarily used as the base of the triple, as there is no consistent answer. It is up to the states.
Interstate Majors and Minors are not the only types of Interstates; there are 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 are East-West, and odds are North-South, except for I-99, which is so annoying. Apparently, Congress specifically picked 99 out of order for this highway, so Congress is the only one who can fix it.
The Interstate Majors are all uniquely numbered, but not so with the Mediums. There are duplicate Mediums, as long as they are far enough away to avoid muddling minds. There are also loads of duplicate Interstate Minors, which is necessary because of the number of densely populated states.
The weirdest one-off is the nice I-69, which goes from Port Huron, Michigan, to Indianapolis, Indiana. It is part of a larger system of I-69s that will eventually connect all the way to the Mexican border. But for now, it’s a weirdly one-off number. There is also 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. Lastly, there is the Long Island Expressway (I-495), which is a one-way spur that should start with an odd digit, but doesn’t connect back to its parent I-95 because Long Island is an island. There is also the confusing Interstate 238, which the number tells you should be a bypass off of I-38, but I-38 doesn’t exist. 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. I-69 splits itself into I-69 East, I-69 West, and I-69C.