U.S. Freeway and Highway Numbering System

The United States has a complex national highway system that is roughly 160,000 miles long. For foreign visitors wishing to drive around, it is helpful to understand how the roads are named and numbered. You never know when this knowledge will come in handy.

Major Interstates

All major freeways that span across several states have one or two-digit numbers. Odd number means the freeway runs north-south, while even numbered freeways travel east and west. For example, interstate 5 (I-5) goes all the way from the Southern border in San Diego to the Northern border in Blaine, WA. I-10, on the other hand, connects the West Coast of San Diego and the East Coast of Jacksonville, FL.

Odd freeway numbers start from the West Coast, and increase toward east. I-5 is the first major north/South freeway, and it sits right by the Pacific Ocean. The next one is I-15, then I-25, and all the way to I-95 which is located along the East Coast.

Even freeway number start from south, and increase toward north. I-10 is the first interstate along the Southern border. Above I-10 is I-20, then I-30, and up until I-90.

Three-Digit Interstates

Three-digit highways connect to other major interstates. For example, 405 is a highway that is connected to I-5, while 215 is off I-15.

If the first digit is an odd number, the highway is likely to have only one end connected a major highway. For example, 710 is a "spur" route that leaves I-10 and goes into the city of Long Beach.

If the first digit is an even number, the highway is usually connected to a major interstate at both ends. 405 splits from I-5 at one end (Lake Forest), but rejoins I-5 at the other end just north of Los Angeles. So they are often referred to as loops or "beltways."

Highway Mile Markers

You may have noticed those mile markers along interstates. They can help you estimate how far you have travelled into a state and how far away you are from your destination.

Mile markers always start at the state line in the south (for north-south highways), or in the west (for east-west highways). So if you enter Oregon from California, you will see mile 1 soon after you cross the state line, and then see increasing numbers as you travel north.

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