Don's Tools · World · US Highway Decoder

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.

Interstate facts: the Interstate Highway System was authorised by the Federal-Aid Highway Act of 1956 under President Eisenhower, inspired by Germany's Autobahn. It comprises about 48,000 miles. The system is designed so any point in the US can be reached from any other without a traffic light (theoretically). Nothing uploaded.

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.