I don't know if I'm opening a can of works with this or not, but here goes...
These are the "Highway N (or N Highway if you're in the KC area)" routes with the square shield, and they are in fact state highways (not county ones like Wisconsin).
Pros:
Help complete the North American highway network
Add routes that may fill gaps in some users files
Cons:
They make up 59% of Missouri's highway network and are mostly pointless (maybe why they went bankrupt?)
Users probably don't drive them to clinch them, e.g. Corco Highways skips them like county routes
Letters do repeat (but not in the same county)
Would probably be very confusing to have in the HB
If no one has started this (and if it's even a good idea to put them in the first place), I'd be willing to do a basic rough draft of these so you guys can focus on more important things.
If this is complete nonsense, you can say so.