While there is no formally approved proposal for tagging highway areas, I'd direct you towards `area:highway` ( https://wiki.openstreetmap.org/wiki/Key:area:highway)
Definitely don't rely on the standard map to drive tagging practise, rendering decisions for the standard map are made based on tag usage.
_______________________________________________ Talk-GB mailing list Talk-GB@openstreetmap.org https://lists.openstreetmap.org/listinfo/talk-gb