MileCheckWhat's the difference between a highway and an interstate?
An interstate is a highway that belongs to the U.S. Interstate Highway System. A highway is a broader term that also covers U.S. routes, state routes, and other major roads.
Every interstate is a highway, but not every highway is an interstate. The difference is the road system it belongs to and the standards it follows, not whether it crosses a state line.
How are interstates different from U.S. highways?
Interstates use red, white, and blue highway shields and are written as I-90 or I-5. U.S. routes use black-and-white U.S. highway shields, such as US 2. The two numbering systems are separate. A U.S. route can cross several states without being an interstate.
The U.S. numbered highway system was adopted in 1926. Its roads can include ordinary intersections, traffic lights, and stretches through towns. Some U.S. routes also have freeway sections. Interstates are generally designed for controlled access, with drivers entering and leaving at interchanges rather than at driveways or ordinary crossroads.
Why are interstates called interstates?
The federal government first authorized designation of an Interstate network in 1944. President Dwight D. Eisenhower signed the Federal-Aid Highway Act of 1956, which launched its major construction and funding program. The system's official name today is the Dwight D. Eisenhower National System of Interstate and Defense Highways.
What do interstate numbers mean?
- Major interstates with odd numbers generally run north to south, like I-5.
- Major interstates with even numbers generally run east to west, like I-90.
- Three-digit interstates serve as connectors, loops, or spurs. The final two digits usually identify the related interstate.
These are numbering rules, not a promise that every stretch of road follows a straight compass direction.
How do interstate mile markers and exit numbers work?
Interstate mile markers generally begin at mile 0 at a state's southern or western boundary and increase as you travel north or east. The count starts over when you enter another state. Many states base exit numbers on mile markers. Others number exits in order, starting with the first interchange.
Knowing the route and mile marker helps you describe a location when you need roadside help. An exit number alone may not tell you how far you have traveled.