I find that I-9 thing annoying. It’s US 1- US 9. Two separate routes.
That's why there's chocolate, vanilla, and rocky road. Iykwim. That said, I myself wouldn't mind separate 1 and 9 signage.
The Maryland SHA did the same thing on the MD 2/MD 4 multiplex in Calvert County in the late '80s when I visited that part of MD. I saw shields for "2-4" all along that stretch. If
https://tinyurl.com/4tvxtmc8 is any indication, the SHA has discontinued the practice, at least on that multiplex.
Plus when are they ever going to shield Tonelle Avenue and properly sign the US 46 interchange in Palisades Park.
As soon as Trenton can afford the Slomin's Shield... oh, wait, we're discussing highway route shields... [blush]