The National Highway was established by the National Highway Act 1974 when Gough Whitlam was Prime Minister of Australia. Before then, while the Federal Government helped to fund major roads, it did not assume direct responsibility for their construction or upkeep.
The National Highway is financed entirely by the Federal Government, though State and Territory Governments are responsible for the actual construction and maintenance of the roads that form part of the National Highway.
The National Highway Act specifies which roads are eligible to become part of the National Highway. To qualify, a road or a series of connected roads must be a direct connection between two State or Territory capital cities. The city of Cairns in the far northern part of the State of Queensland is also included in the National Highway Act. Part of the National Highway system is also in Tasmania, where National Highway 1 connects the State's capital city, Hobart, with the city of Burnie, the main seaport for freight traffic to and from the Australian mainland.
Some of the well-known highways that are part of the National Highway include the Hume Highway, the Bruce Highway and the Eyre Highway.
National Highways are denoted by a route marker in the shape of the shield found in the Australian coat of arms. The word "NATIONAL" is printed in the upper portion of the shield above the highway's number. The shield, text and number are coloured yellow while the background is dark green - Australia's national colours.
National Highway numbering originates from the earlier National Route network. Many of the routes that are now National Highways with the signature green and gold sheilds, continue beyond the official National Highway as the black and white shielded National Routes. Certain streches of the National Highways have "A" and "M" tag on their shields; particularly those in Victoria and South Australia. They have completely revised their route numbering, basing it on the British M, A, B, C classifications. These states have retained the original National Highway numbering and shield decal, having added the appropriate M and A classification.