In South Australia, Highway 1 is a 1,715-kilometre (1,066 mi) 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.

Australia's Highway 1 is a network of highways that circumnavigate the country, joining all mainland capital cities except the national capital of Canberra. At a total length of approximately 14,500 km (9,000 mi) it is the longest national highway in the world, surpassing the Trans-Siberian Highway and the Trans-Canada Highway. Over a million people traverse some part of the highway network every day. It is the longest continuing highway in the world as the Pan-American Highway is separated by the Darién Gap and AH1 is separated by the Sea of Japan.