Not all transcontinental interstates will end in 0 or 5 - interstate 69 is planned from mexico to canadia.

Thanks Ed - I completely forgot 3 digit interstates. But you are sorta wrong - it is much simpler. An odd first digit should mean it is a spur - only one end is at another interstate. An even first digit means both ends are at other interstates. This usually happens but sometimes like in california there are too many 3dis and not enough 2dis. Of course the last 2 digits are the parent interstate. kurumi.com has more info.

But that is a very interesting theory!

A hundreds digit of 1 is a local spur into a city. A hundreds digit of 2 is an express through a city. A hundreds digit of 3 is a bypass between highways. A hundreds digit of 4 is an express around a city. A hundreds digit of 5 is a local spur into a city. A hundreds digit of 6 is a wide bypass around a metropolitan region. A hundreds digit of 7 is a wide bypass around a metropolitan region. A hundreds digit of 8 is an express through a metropolitan region.

no offense