US highway decoder
Type any Interstate, US Route, or State Route number to decode what it means - direction, type, and where it runs.
🔵 Interstate Shields
Red, white and blue shield. Odd numbers (I-5, I-95) run north-south. Even numbers (I-10, I-80) run east-west. Low numbers start at the south and west coasts; high numbers are in the north and east.
3-Digit Interstates
A 3-digit interstate is a spur or loop of its 2-digit parent. If the first digit is even, it is a beltway or loop that returns to the parent highway (e.g. I-285 loops Atlanta). If odd, it is a spur that dead-ends into a city (e.g. I-195 into Miami).
🛡️ US Routes
Black and white shield. Odd numbers run north-south; even numbers run east-west. US-1 runs the entire East Coast from Maine to Florida. US-101 runs the Pacific Coast. Unlike interstates, US Routes predate the Interstate system and pass through city centers.
Numbering by Region
Interstates: 1-19 Southeast, 20-39 South, 40-59 South-Central, 60-79 Midwest, 80-99 North. US Routes: 1-49 East, 50-99 Southeast, 100s-200s South-Central, 300s-400s West.
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How to use US highway decoder
Enter your figures
Fill in Interstate US Route State Rt. Values you change are used straight away, with no submit button.
Read the results
The 🔵 Interstate Shields, 3-Digit Interstates and 🛡️ US Routes update as soon as a value changes.
Start over any time
Nothing is saved on a server, so reloading the page clears everything.
What this tool does
Decode any highway number
Type an Interstate, US Route or State Route number and it explains what the number means and roughly where the road runs.
Learn what odd/even numbers mean, how 3-digit interstates work, where major routes run, and what the shield colors indicate
Odd numbers run north to south and even ones east to west, three-digit Interstates are spurs and loops off their parent, and the shield colours mean something too.
Interstate, US Route or State Route
The three systems number their roads by different rules, so you pick which one you are asking about first.
Runs fully in your browser with no upload and no sign-up
The rules and the route list are held in the page, so nothing you type is uploaded and it works with no connection.
Frequently asked questions
Why do interstates run in the opposite direction from their numbers?
Odd-numbered interstates run north-south with low numbers in the west and high in the east. Even-numbered run east-west with low numbers in the south and high in the north. The opposite of how you might expect. It is intentional - the numbering grid makes it easy to figure out roughly where any interstate is just from its number.
What is the longest and shortest interstate?
I-90 from Seattle to Boston is the longest at about 3,020 miles. The shortest is debated - I-878 in New York is less than 2 miles.
Why are some interstates missing numbers?
Numbers are reserved for future use, or were retired when routes were decommissioned. For example I-50 and I-60 were skipped to avoid confusion with US Routes 50 and 60 in overlapping areas.
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