DaveNay said:
I was really always under the belief that the Interstate numbers are always unique, even going so far as changing some designations to make sure they are unique.
There's a lot of I-190's and I-290's since the "90" section of the number denotes that it's coming off of the main road of I-"90".
The primary interstate #'s are unique.
Here's how the interstate #'s work.
- Interstate north-south routes have odd numbers, with numbers increasing from west to east.
- Interstate east-west routes have even numbers, with numbers increasing from south to north.
- Interstate highway routes have one- or two- digit numbers.
- North-south interstates ending with a 5 and east-west interstates ending with a 0 are typically major cross-country routes.
- A three-digit interstate always ends with the two-digit number of the main interstate it loops off from, except I-238.
- Three-digit road numbers beginning with an even number are either beltways that go around a city or freeways that go through a city.
- Three-digit road numbers beginning with an odd number branch off the main interstate.