I posted this as a comment on one of your videos, but I'll post it here as well.
I think it would be nice if you were to also do US highways, such as US 97 and others, and local state highways, such as WA 14, OR 35, and others. While not exactly like interstates, they still have signs saying X points are in Y miles and the like. I would love to see your thoughts on those as well.