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

It’s effectively part of Highway 1 - which goes around the coast through every coastal city on mainland Australia.

It’s not officially part of it, but west of Cairns a bridge has been closed to a lot of traffic for three years. Most people don’t expect the bridge to be repaired, more likely they’ll move the highway… but preliminary investigations have been suppressed (not a good sign) and nearly $10m is being spent just on planning to decide what to do - the results of that planning effort are scheduled to be released by the end of next year - who knows when construction will start. In the mean time, Atherton-Malanda Rd is one of the detour options, depending where you’re going along Highway 1.

It’s also a major tourist road - about half a million tourists per year drive along it.

You’re right, it’s not a major highway. But it is and always has been used for heavy freight and more than ever since the bridge is a mess. It was originally built well over a hundred years ago to haul massive old growth rainforest tree trunks to be shipped off to Europe - I’m talking trees where a single log would need an oversize truck to move it by modern standards. These days the road is depended on by local farmers and it’s almost a blessing that it’s not a federal highway, because being a local road means it’s actually considered a priority by the government that maintains it.