Interstate highways that go predominantly north to south have odd numbers. The lowest numbers (such as Interstate 5) are on the west coast of the U.S, and progressively get higher as you go east (for instance, Interstate 95 runs between Maine and Florida on the east coast of the U.S.). Interstate highways that go predominantly east-west have even numbers. The lowest numbers are in the southern U.S., getting higher as you go north. (For instance, I-10 runs across the southern states of the U.S.). Three digit numbers (such as Interstate 495) are connector highways, or highways that go around a metropolitan area. The numbers are assigned when a new Interstate highway is being planned, in cooperation between the US Department of Transportation and state highway departments. At this point, virtually all of the Interstate highways that were planned have been completed, so there are few new numbers being assigned. This numbering system replaced a more confusing system used for the “US Routes”, such as “Route 66″ that were used before the Interstate highway system was constructed.
