In South Australia, Highway 1 is a long route that follows the coastline of the state, from the Victorian border near Mount Gambier to the Western Australian border near Eucla. Highway 1 continues around the rest of Australia, joining all mainland state capitals, and connecting major centres in Tasmania. All roads within the Highway 1 system are allocated a road route numbered M1, A1, B1 or R1, depending on the state route numbering system. In South Australia, most of the highway is designated as route A1, with multi-lane, dual-carriage-way sections generally designated route M1, and the alignment around the Adelaide CBD designated route R1. South-east of Tailem Bend, it is designated route B1.
Highway 1 was created as part of the National Route Numbering system, adopted in 1955. The route was compiled from an existing network of state and local roads and tracks. It was meant to be a National Route between the Victorian Border near Mt. Gambier and Adelaide. In 1958, it was extended northward from Adelaide to Port Augusta, and westward, toward the Eyre/Lincoln highway junction. The Eyre Highway, the Port Wakefield-Port Augusta Road, Port Wakefield Road, and the South Eastern Freeway were declared National Highways in November 1974. Since, the route has remained static.
In South Australia, the highway connects: