OpenStreetMap-Americana, an American-styled OSM map style with Highway shields!

[vdeane]

Another interesting scheme: MapArt used blue for freeways and purple for toll roads.  Seems appropriate given the coloring of signage for AET facilities.  If anyone's curious, my AAA atlas is Kappa Map Group.  I also have a Hagstrom atlas of NYC that used green for parkways (which makes sense to differentiate due to restrictions on commercial vehicles).

[MoiraPrime]

Couple of notes: I had to zoom in quite far to see some of state route numbers, rendered shield or placeholder square. Some, like OR 18 and OR 62, actually said 'OR 18' or 'OR 62' in their shield.

That usually indicates someone tagged the relation of those routes wrong. They're supposed to have network=US:OR with ref=18 or 62.  Sometimes people will mistakenly set the ref on the relation to OR 62. It should only have the state abbreviation on the ways.