Have you ever found yourself lost on an interstate, staring at a maze of signs and wondering how to get back on track? You're not alone! Navigating the U.S. highway system can feel like deciphering a secret code, with every number and symbol holding a unique meaning. Imagine looking at an interstate map—it often resembles a chaotic doodle across the United States, right? No wonder it’s confusing, especially in our information-overloaded world. But don’t worry, we’ve got you covered. In this guide, we’ll unravel the mysteries of highway signage and help you understand everything you need to know to travel confidently on our U.S. highways.
Our highway numbering system has existed since 1926, gradually getting more complex as our interstate system did. While this is the base of the numbering system, the official interstate system started in 1956 and took decades and a half-trillion to build. Now, this system supports about 25% of our vehicular transportation. In general, highways that run north to south are odd numbers, increasing from east to west. This is nearly reversed when traveling from the other direction: even numbered highways with numbers that will increase from north to south. Each state’s mile markers usually start at the western- or southern-most edge of a state. For our nation’s interstates, the numbering system is done oppositely, the largest odd number runs along the east coast with the smallest cutting from Seattle to San Diego. The largest even numbered interstate is in the north, with the smallest (I-10) starting in Texas. When we get into state, territorial, county, and secondary highways, there’s a lot more variables to consider, making their signage not as straight-forward.
If you find yourself confused by all of the highway signs in a major city, here’s some help decoding all of those numbers. Major two-digit interstates that end in fives and zeros are unique: there will only be one I-95 and one I-10. Other two-digit interstates can be repeated as long as they’re located far enough apart: I-76 exists in both Pennsylvania and Colorado. If an interstate has three digits, these are shorter interstates that serve metro areas specifically, but will connect to the longer two-digit routes and are often beltways, spurs, or connectors. When you see an interstate with three digits, the final two digits are the same as the route it connects to: I-270 will meet with I-70, for example. The first digit explains the purpose of the road. If the first digit is an even number, the interstate is a loop or a bypass. Odd first digits are representative of spurs and connectors. For this reason, you can see the same three-digit interstate in a number of states, regardless if the states are touching.
If all of that was clear as day, let’s talk about when the rules don’t apply. There are a few exceptions to the rules, like Maryland’s I-270: a spur that connects to I-70 but starts with an even number instead of odd, like all other spurs. In the San Francisco Bay Area, I-238 connects I-580 and I-880—there isn’t even an I-38. California should have named the interstate an odd number followed by “80”— but all options from one through nine were already assigned to other highways and since the interstate was previously just a state route, the number stayed after its conversion.
Let’s get back to those state, territorial, county, and secondary highways. Since every state has its own highway system, state markers are used to indicate these. Sometimes this is through the use of their own state shape, variations of the state flag, or icons that somehow reflect the state, being a major visual element of the state highway signage. If a state highway becomes so heavily traveled that it’s upgraded to a federal interstate, then it will earn the same red, white, and blue interstate shield that we often associate with our interstates. If a state doesn’t have state-specific signage, then a state highway is indicated with a circle: which is important to know since the “circular highway shield” is how state highways will be shown on most maps and atlases.
The other highway systems are even more broken down. Every state has a highway system, but only some states have a secondary highway system. These are built to supplement the main system if needed: “For example, Texas established a system of farm-to-market roads to specifically improve access to rural areas. Nebraska has Connecting Link, Spur, and Recreation Highways to provide access to small towns and state parks. The Missouri supplemental route system was designed to provide access to most farm houses, schools, churches, cemeteries, and stores within the state.” Territory highways are for places that aren’t states, but instead federal districts or territories. These areas have signage specific to them in order to keep the state highway number system in tact, and to signify their location while still following our highway number rules. County highways are managed by a county, which can vary significantly across the country. This means a county highway can be paved or a dirt road and be funded in a variety of ways—which we won’t get into here. These highway signs will often say “county” on them, unless you’re in Louisiana, where a county is instead called a “parish.”
At Interstate Signways, we see them all: from major interstates that run across the nation and state highways with all of their different shields, colors, and images, to small highways for territories, counties, and secondary highway systems. We see them all because we make them all! No matter the journey, remember that Interstate Signways was here marking the way!