How the US Highway System Works

Photograph by Kay Gaensler


Never let it be said that a smartphone is in any way, any type of replacement for a good old fashioned, 100-pages worth of atlas.

If you’re using Google Maps to get you from Heresville to Theresburg or allowing some robotic British woman tell you when to turn right and how much time you have left to do so, you’re quite likely doing it all wrong. Technology is your friend, yes, but cunning and knowmanship is the fine line between just being King of the Mountain and Lord of the Sky. There’s a big difference there. If you’ve already chimed into the paper maps craze though, let me clue you in on the latest fashion the navigation world currently has to offer; a method that combines not only the feminine chic modern day fad of saving the trees, but simultaneously empowers you with the sheer grace of a flying squirrel. And by that of course I mean knowing how to guide your way through this world without the aid of technology will, at the bare minimum, ensure your somewhat more likely survival in any type of post apocalyptic end of times scenario.

Let’s drive it on home, shall we? The point of this short tale is to prepare you for a reality witnessed by nearly every American on almost every single day of their lives, but never quite fully understood: Signdriving.

Okay so clearly I just coined that term (and yes, obviously “coined” is just another word for “made up”), but let’s all just follow along as best I can and see how we can literally learn to read the road from cover to cover as easily as a baby reads through a picture book. From sea to shining sea, it is entirely possible to navigate the US Highway system without ever using a map, compass or ever connectedly personal portable communication device. Fact.

The History

Firstly, we should thank our forefathers. Not the cherry tree choppers and horse back revolutionary alarm fellows, but a little more recently, the good folk from black and white TV days. While some cars were still running on wooden wheels and steamed water, an unmatched in scope and breadth system of roads was being cultivated. A transcontinental permanent fixture on Mother Nature, spanning the New World, whereby travelling salesmen,  anti-prohibitionist entrepreneurs and wanderlusting dads dragging their families along alike could roam from state to state with nothing between them and the open road but the wind through their toupees. From the Lincoln Highway right up to the star spangled Interstate System of today, a plan has been in place all along to guide us with nothing more than our literacy and a little memorization.


Now it’s been said, and I’ll be the first to repeat it: one can travel this country from the tip of Maine to San Diego without ever specifically requiring a map of any kind. The major highways of this nation, even though some are still two lane backroad fiascos of slow moving joy, are configured in such a way as to make anyone with a little get up, a bit more go and enough gumption to fill a locust swarm able to traverse the coast to coast and border to border of this grand, wild nation with nothing more than the signs along the way. That having been said, of course, some basic skills will come in exceptionally handy.

The Sun. Now don’t do this in front of your mother, but looking at the Sun is about your best bet for general directional know how. If you wake up in the morning (that is, just around after sunrise) and are aware of just about when sunset will come, you can follow these guidelines. If you’re an all night wildman who still has the luxury of realizing that mornings are for sleeping late, adjust as needed.

General Sense of Direction. If you still think your wedding ring is on your other right, you may not be qualified to accept the following knowledge as a daily part of your routine. That’s okay, that’s why God made significant others. Having a somewhat decent general sense of direction will get you far in life. In fact, you usually can’t get very far at all without it.

How it Works

Let’s get down to the details, shall we. Firstly, it’s all about numbers. On the highway, numbers mean everything. Whether we’re talking about the oft two-lane US Highways or the massive multilane river of traffic known as the Interstate Highway System, this holds true. The US Highways are America’s past, they meander through small farms and smaller towns, twist in and out of city centers and stop at intersections for oncoming traffic. Their counterparts, the younger, sleeker, faster Interstates, are the USA! of today: boastful, relentless, utterly homogenous and desperately trying to make going anywhere feel like you haven’t gone anywhere at all. Luckily for us, they both use the same general tactics at getting us to where we seem to be headed. Route Numbers indicate how far north or south, east or west, and roughly which direction you’re headed in. Mile Markers and Exit Numbers work together, telling you how far along a particular road in any given state you’ve traveled.  Listen to the road. Read the double yellow lines. And remember, it’s always easier to head South or West without an atlas.

Route Numbers

Every highway has a route number. Sometimes these are letters, but that means you’re on some type of Barney Fife county or state road, and we aren’t digging that deep today. With US Highways and the Interstate, they come with clear rules.

Evens vs. Odds. Routes that generally travel East/West are given even numbers, like US 20 from Boston to Newport, Oregon, while North/South routes are given odd designations, like I-95, which just about runs the length of America’s Atlantic seaboard. Keep in mind that for reasons of practicality, highways swerve and sway to avoid downtown traffic, connect to nearby routes and generally avoid plunging off of cliff sides, but big picture thinking here, this rule holds true. Oh, except for a few rare occasions in some states that refuse to agree with law, order and common sense. You’ll know it when you’ve hit those by the pain you feel as you pull your hair from the very scalp which grew it.

Numerical Order. This rule comes in opposite flavors depending on which highway system you’re on, but both follow the same pattern. The number of the highway you’re on tells you where on the landscape of America you are.

How many digits? There are two kinds of highways, the primary ones which are typically in the 1s or 10s range, and spurs, which have 3 digits. Primary routes are like US 30, US 6, I-10, and I-5. Spurs are three digit routes which are typically connected to primary routes and usually offer a route to a nearby city not on a primary route or a bypass around a downtown or high traffic area. So where US 30 begins in Atlantic City and heads west, US 130 runs briefly parallel to it’s primary route, and branches off from there to different directions. Similarly, where I-95 runs seriously through the heart of Jacksonville, Florida, I-295 does a wide loop around the city to help travelers headed further south avoid city traffic. For those of you really following along, the big exception is US Route 101, which isn’t a 3 digit route, but a specially designated 2 digit route made up of three numbers…confusing, yes, but just remember: US 101 is so very incredibly special, and it runs the rim of the three most liberal states in the country; it can do what it wants. So where US 201, 301, 401, etc. are spurs of US 1, US 101 is all on it’s own.

An infographic detailing how to use the US Highway system's signs to navigate the United States without a map


Mile Markers

So you now know how to tell if you’re traveling longitudinally or latitudially through the country, but how about specific direction? Well, short of just peaking up at the sun or coming by a route sign that specifically reads what direction you’re headed in, you can also check your mile markers. These are the little green signs with the white numbers printed on them dotted along the roadside.  Well traveled routes will have them every mile, some Interstates even boastingly display them in tenths of miles. Back country US Highways will spread them out as thinly as one every twenty miles or so. But either way, if you can find them, you can tell your specific direction.  Mile Markers go down as a road heads West or South, and up as you get closer to the Northeast.  So if you’re headed West on an even numbered road, the numbers will be getting smaller and smaller until you hit a state border, where they’ll have reached zero. Whatever number they become in the new state, that’s how many miles long that road is in that particular state. Same holds true when you’re headed South. Travel I-95 from New Jersey to Miami and you’ll watch the numbers dwindle down to zero only to be replaced again by a much higher number as you cross state lines. You can easily judge how much time you have left in a state by the number of miles left on a road that passes the entire breadth of the state’s boundaries.  Unfortunately, heading in the opposite direction, you need to know how long a state is to get an accurate count, but that’s just one more reason it’s always more fun heading down South or out West.

Exit Numbers

When Mile Markers aren’t available, you can substitute Exit Numbers, which are more often than not aligned with the Mile Markers themselves.  If you know that your destination is at Exit 109 and you’re at Mile Marker 159 headed West, you’ve got fifty miles to go. Headed North on I-77? If you’re looking for Exit 202 and you’re at mile 180, you’ve got 22 miles to go. Sometimes you’ll see exits marked as “Old Exit 20”, nevermind that. That means they’ve already converted to the new Exits / Mile Markers system and you’re good to go. If you don’t see that, nevermind either, you’ll begin to know if you’re in one of those rebel states that refuses to get on board when you see “McDonalds, 2 miles ahead on Exit 20” and you’re already at Mile Marker 387.


Billboards are the fart smear on the Marilyn Monroe’s face of America. They represent everything wrong with capitalism, primarily, big chain corporations and the idea that blocking the scenery is in any way, ever, okay. But for navigational purposes, they can sometimes come in quite handy. For example, when you see a sign that reads “JR’s Cheap Tobacco, Exit 59” that can clue you in to how far you have to go until you get there. Billboards rarely provide any information that any of the above methods do, but when you’re in Apache Country, Arizona and no government official has bothered to update the road signs since CHIPS got canceled, sometimes advertising can provide as many clues as Sherlock Holmes would ever need.

Notable Exceptions to the Rules

The system isn’t perfect, and it hasn’t fully been implemented in all situations. Sometimes states just refuse to cooperate (ahem, damn you the South!) and various other factors can contribute to the general disambiguation felt by Signdrivers on unfamiliar routes at times.

US Route 101 shieldUS Route 101

Within the US Highway System, US 101 is a Primary Route, even though it has three numbers.

Interstate 99 Red, white and blue shieldI-99

Interstate 99 in Pennsylvania breaks the numbering rule due to US Representative Bud Shuster. Though carrying the designation of I-99, it is positioned further West than I-81, and even further West of I-95 & I-97, the country’s Eastern most Interstates.


Interstate 97 Red, white and blue shieldWhile not specifically an exception to any rules, I-97 is the only Interstate in the country which runs through a single county. It runs for 17.62 miles through Anne Arundale County in Maryland. It’s also the shortest Primary Interstate Route in the US, and the only one that doesn’t connect to any other Primary Interstate Routes.


Interstate 238 Red, white and blue shield This road is riddled with exceptions. Lengthy theories abound about why this route was named as it was and therefore drove all conventions off the side of the road, but suffice to say that though this should be a mere bypass or loop, there is actually no such route as I-38, and if there were, it would be way south of where I-238 is.

Sequential Exit Numbers

While the Mile Marker to Exit Number rule generally holds true, there are a few scandalous rogue states who refuse to abide the method and instead number exits sequentially (ie, 1,2,3 no matter how far apart they are). When traversing New England, proceed with caution: Connecticut, New Hampshire, Massachusetts, Rhode Island and most of Vermont use sequentially numbered exits. New York mostly follows suit. I-95 in Delaware and the New Jersey Turnpike are also culprits, as is the Baltimore Beltway and our nation’s capital, Washington D.C.