South Australia can be thought of as having two parts; the fertile farming economy surrounding Adelaide in the south and the much more arid northern portion. The road network in the south tends to be well developed, with paved roads going more or less east-west to NSW and WA. Northerly roads tend to be gravel or dirt, such as the Birdville Track, and the north-westerly roads tend to pass through land ceded to aboriginals and require permits.
Northern Territory occupies the second side. It is state-like, if not legally a state, and occupies a huge area. The north-south highway from Darwin through Alice Springs to SA is the main transportation route of the territory, with one highway going to NSW and a partly-paved one to QLD.