If it were a major interstate route, it would have a name

It’s effectively part of National Route 1 - the highway route that goes around the coast through every coastal city on mainland Australia.

It’s not officially part of it, but Route 1 has a bridge that was partially closed three years ago — reduced to one way traffic with lights on either end, and load limits that block it from being used by heavy vehicles. It doesn’t seem like the bridge is going to be fixed - they’re likely to move the highway instead. In the mean time (and possibly permanently), Atherton-Malanda Rd is the detour for most of the traffic that used to take National Route 1.