Aug 19, 2013

The numbering system used for U.S. Highways

Odd-numbered highways move north and south, while those with even numbers move east and west. Highways with one- or two-digit numbers are through routes, often long ones used for distance driving. Three-digit routes that begin with an even number are usually beltways around a city. Three-digit routes that begin with an odd number are spur routes in a city or town. (The Book of Answers, by Barbara Berliner)