I, too, am interested in such trivia and the facts around our roads. Here is a link I have in my favorites folder:
Interstate GuideHistory, pictures, specifications, listings by route number, etc. Enough to keep you occupied when you're not planning your next camping trip,
There's a similar page for US highways:
US Highway GuideLowsuv wrote:
I still call the Banfield Interstate 80.
It has been Interstate 84 for 34 years now
In the "old days", there were interstates named I-80N (like in Portland, OR) and I-80S where I-80 was split into two different routes. They did away with the N and S designations and the result was highways like I-84 in OR and I-76 in CO plus others. That's part of the reason there are split routes as originally noted by the OP.