How Interstate Highways Are Numbered in the US

GeoGlobeTales provided a very quick but effective tutorial on the seemingly confusing logic behind the interstate highway numbering convention within the contiguous United States and offered helpful hints on how to remember which roads go where.

The farther southwest you are, the lower the highway numbers, and as you move northeast, the numbers get higher. Highways ending in 0 indicate horizontal routes, while those ending in 5 indicate vertical routes.

He also addresses the interstate minors (three digit numbers).

Additionally, the interstate minors, which are branches off the major highways marked with three-digit numbers. The last two digits match the major highway number. If the first digit is even, the branch loops back to the major highway; if it's odd, it doesn't reconnect.

via Chris Messina