US Highway Map: The American Road System Explained
Interstates, US Routes and state highways all share the same road map — but they are three different systems, numbered three different ways. Here is how to read any US road map.
Last reviewed on August 26, 2026
Anyone reading a US highway map is looking at several networks layered on top of each other. Blue-and-red shields mark the Interstate Highway System. White shields shaped like a badge mark the older US Numbered Highways — US 1, US 66, US 101. Coloured squares and circles mark state routes, and below those sit county and local roads. Once you know which shield you are following, the numbers themselves tell you which direction the road runs and roughly where in the country you are.
The three levels of the US highway system
| System | Marker | Approx. length | Built for |
|---|---|---|---|
| Interstate Highways | Blue and red shield, "I-" prefix | ~48,756 miles | Controlled-access, long-distance and freight travel |
| US Numbered Highways (US Routes) | White badge shield, "US" prefix | ~157,000 miles | Cross-country travel through towns, pre-dating the interstates |
| State highways | State-specific shield or circle | Varies by state | Connecting towns and counties within one state |
All three carry through-traffic, and many share pavement: a single stretch of road can be signed as I-80, US 30 and a state route at the same time. Only the interstates are guaranteed to be limited-access with no traffic lights or driveways.
How US Route numbers work
The US Numbered Highway system was laid out in 1926, three decades before the first interstate, and it uses the opposite numbering logic to the interstates — a detail that trips up a lot of map readers.
- Odd numbers run north–south, starting with US 1 on the Atlantic coast and climbing westward to US 101 on the Pacific.
- Even numbers run east–west, starting with US 2 along the Canadian border and climbing southward to US 98 on the Gulf.
- Three-digit US routes are branches of a parent route: US 287 splits from US 87.
- Numbers ending in 0 or 1 historically marked the major transcontinental corridors — US 20, US 30, US 40, US 50, US 60.
Interstates flip this: interstate numbers grow from west to east and from south to north. That is why I-10 runs across the southern border states while US 10 sits up near the Great Lakes, and why I-5 hugs the West Coast while US 5 is in New England.
The longest US Routes
US 20 — about 3,365 miles
The longest road in the country, running from Boston, Massachusetts to Newport, Oregon, and passing the northern edge of Yellowstone. A closed section through the park means it is not continuously driveable end to end.
US 6 — about 3,205 miles
Provincetown, Massachusetts to Bishop, California. Once the longest highway in America, it was truncated in 1964 when its California section was replaced by interstate.
US 30 — about 3,073 miles
Atlantic City, New Jersey to Astoria, Oregon, following much of the old Lincoln Highway, the first road built for cars all the way across the country.
US 50 — about 3,007 miles
Ocean City, Maryland to West Sacramento, California. Its run across Nevada is signed "The Loneliest Road in America".
US 66 — decommissioned in 1985
Chicago to Santa Monica, 2,448 miles. Route 66 no longer appears on official highway maps; its path is now covered by I-55, I-44, I-40, I-15 and I-10, with long stretches signed as Historic Route 66.
Reading a US road map
Shield shapes
The shield is the fastest way to tell the systems apart. Interstates use a blue shield with a red crown and white numerals. US Routes use a plain white shield, usually on a black square. State routes vary wildly — California uses a green spade, Texas a white square with the state outline, Florida a circle.
Mile markers and exit numbers
On interstates, mile markers count up from the south or west edge of each state and reset at the state line. Exit numbers usually match the nearest mile marker, so the gap between exit 40 and exit 95 is roughly 55 miles. US Routes are mile-marked far less consistently, and many states do not mark them at all.
Business routes and bypasses
A "Business" plate above a shield means the route detours through a town centre and rejoins the main road. A "Bypass", "Loop" or "Alternate" plate means the opposite. Both carry the same number as the parent route, which is why a single town can have three roads all numbered 30.
Toll roads and turnpikes
Roughly 6,000 miles of the US highway network is tolled, concentrated in the Northeast and around large cities. The Pennsylvania Turnpike, New Jersey Turnpike, Ohio Turnpike, Florida's Turnpike and the Illinois Tollway are all interstate-standard roads that charge. Most now use electronic transponders — E-ZPass in the east, SunPass in Florida, FasTrak in California — and several no longer accept cash at all.
Frequently asked questions
What is the difference between a US highway and an interstate?
An interstate is a controlled-access freeway built to federal standards after 1956, with no intersections or traffic signals. A US highway (US Route) is an older numbered road that may run straight through the main street of a small town, with stop lights and driveways. Both are federally numbered; both are maintained by the states.
Is there a single map of every US highway?
The Federal Highway Administration publishes the National Highway System map, which shows interstates, US Routes and other principal arterials together. For route-by-route detail, this site's interstate highway map covers the interstate layer, and each state page lists the main highways crossing that state.
What is the longest highway in the United States?
US 20 at about 3,365 miles is the longest road overall. Among interstates, I-90 is the longest at 3,020 miles, from Seattle to Boston.
Do US Route numbers ever change?
Yes. The American Association of State Highway and Transportation Officials approves additions, extensions and decommissionings each year. US 66 is the best-known removal; US 400 and US 412 are relatively recent additions.
Which state has the most highway miles?
Texas has by far the largest state-maintained highway network, followed by California. Texas also carries more interstate mileage than any other state, at roughly 3,500 miles.
Keep exploring
- US interstate highway map — interactive map of every interstate route, with numbering rules and the longest highways.
- US map with major cities — the cities these highways connect, ranked by population.
- US time zones map — essential for estimating arrival times on a long cross-country drive.
- US national parks map — plan a road trip around all 63 parks.
- All 50 states — geography, major cities and highways state by state.
- Printable US maps — print a road map for the car or the classroom.