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How are United States highways numbered?

Interstates are multilane, divided highways. The main north-south interstate highways always have odd numbers of one or two digits. The system, beginning with Interstate 5 on the West Coast, increases in number as it moves eastward. It ends with Interstate 95 on the East Coast.

The east-west interstate highways have even numbers. The lowest numbered highway begins in Florida with Interstate 4, increasing in number as it moves northward. The highest-numbered east-west interstate is Interstate 96, which begins in Michigan. East-west interstates that run coast-to-coast—such as Routes 10, 40, and 80—end in zero. An interstate with three digits is either a beltway (a roadway around a major metropolitan area) or a spur route (an offshoot of an interstate).

U.S. routes, which are two- or three-lane, undivided highways, follow the same numbering system as the...

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