Tagging for highway routes in Australia is documented at [1]. That section doesn’t discuss route names specifically, but those numbered routes very frequently come with signposted names that are distinct from the names of the streets that carry the route. This is similar to the distinction between roads/streets and routes in many U.S. states.

I mentioned route=street because this changeset had replaced many occurrences of type=route route=street with type=street. As far as I can tell, route=street wasn’t causing any problems, but using route=road for this purpose would dilute an important tag for renderers and routers.

Some renderers such as OsmAnd and OSM Americana display shields based on route=road relations or render certain networks at lower zoom levels. Routers such as OSRM and Valhalla modify guidance instructions when they encounter route=road relations. [2]

This discussion is getting rather unwieldy for a narrow comment box. Perhaps we can take this to the forum if you’re interested in discussing further?

[1] https://wiki.openstreetmap.org/wiki/Australian_Tagging_Guidelines/Roads#Routes
[2] https://github.com/Project-OSRM/osrm-backend/blob/31e31a63d062fb804f5f4695ed3036ca7a269ead/features/car/route_relations.feature#L238-L248