How are interstate highways numbered?

Question

What system is used to call number the interstate highways across America?

Answer 1

Odd numbers indicate North-South routes (ex. I-95, I-5). Even numbers indicate East-West routes (ex. I-10, I-90).

The highway system is the Dwight D. Eisenhower National System of Interstate and Defense Highways. This was done since the US routes were getting crowded and dangerous in the 1950s.

Answer 2

How Are Interstate Highways Numbered

Answer 3

The big routes end with 5 or 0. In the case of the 5's, the numbers increase as you go from West to East. Route 5 hugs the West Coast, Route 95 hugs the East Coast. For the 0's, the numbers go up as you go north. Interstate 90 goes from Boston to Seattle.

This was done because the old, non-Interstate national highways were done the reverse way. For example, U.S. 20 goes from Boston to the West Coast. I believe there is no I-50, because the planners didn't want any confusion with U.S. 50 in the middle of the country.

The other numbers follow that pattern, more or less, and fill in the gaps. I-81 goes from Canada to Tennessee. I-87 goes from Montreal to New York. And so on. Sideroads off the Interstates get a third digit. The first road off I-90 in New York is I-190, located in Buffalo. I-390 is in Rochester, I-690 is in Syracuse, I-890 is in Albany.

Answer 4

Odd numbers run north and south. Even numbers run east and west. Smaller numbers start in the south. I-10, I-20. etc. Smaller Numbers start in the west, I-5, I-15, I-25, etc.

Answer 5

East to West are even numbers
North to South are odd numbers, and folks wanta know what makes us southerners odd. well there ya go!