MileCheckUS highways vs interstates: what's the difference?
They're both numbered highways with shields and mile markers, but they're two separate systems built decades apart — and their numbers run in opposite directions across the map.
Two systems, two eras
The US Highway system (US Routes) came first, established in 1926. The Interstate Highway System began in 1956 as a network of high-speed, limited-access freeways. Many US routes are older two-lane roads that run right through towns; interstates are built to a uniform freeway standard — divided, grade-separated, no stoplights or cross traffic.
How to tell them apart
An interstate uses the red-white-and-blue shield and is written "I-5" or "I-90." A US route uses the plain black-and-white shield and is written "US-2" or "US-101." A US route can be anything from a full freeway to a small-town main street with traffic lights; an interstate is always a controlled-access freeway.
The numbering runs opposite ways
Both systems use the same direction rule — odd numbers run north–south, even numbers run east–west — but the low-to-high order is reversed between them. Interstate numbers increase west to east and south to north (I-5 on the West Coast, I-95 on the East Coast). US route numbers do the opposite, increasing east to west and north to south (US-1 down the East Coast, US-101 on the West Coast; US-2 near the Canadian border). That's why an interstate and a US route with similar numbers can be on opposite sides of the country. More on how interstates are numbered →
Mile markers work the same on both
Whether you're on an interstate or a US route, mile markers count up from 0 at the state's southern or western edge and reset at each state line. So "US-97 at mile 154 in Oregon" pinpoints you exactly the same way "I-84 at mile 210" does. The MileCheck app reads your mile marker on both systems in real time.
Know exactly where you are — live
Your mile marker shows even offline. Live state DOT feeds and the nearest camera on your route are part of MileCheck Premium and need a connection to update. Runs on CarPlay and Android Auto.
Questions, answered
What's the difference between a US highway and an interstate?
Interstates are limited-access freeways built to a uniform national standard (I-5, I-90), using the red-white-blue shield. US highways are an older system (US-2, US-101) with the black-and-white shield that can be freeways or ordinary roads with intersections and traffic lights.
Is US-101 an interstate?
No. US-101 is a US route, not an interstate — it uses the black-and-white US shield. It runs along the West Coast and is a US highway despite being a major road.
Why do US route numbers go the opposite way from interstates?
Interstate numbers increase west-to-east and south-to-north; US route numbers increase east-to-west and north-to-south. The two systems were numbered in opposite orders, so a US route and an interstate with similar numbers can be on opposite coasts.
Why are interstates called interstates?
Congress first authorized an interstate network in 1944, and the Federal-Aid Highway Act of 1956, signed by President Eisenhower, funded its construction. The official name is the Dwight D. Eisenhower National System of Interstate and Defense Highways. A road does not have to cross a state line to be an interstate; it has to belong to that system.
Is every highway an interstate?
No. Every interstate is a highway, but "highway" also covers US routes, state routes, and other major roads. The difference is the system a road belongs to and the standards it is built to.
Do US highways have mile markers?
Yes. US routes use the same mile-marker system as interstates — markers count up from the state's southern or western edge and reset at each state line.