About the national road networks
The National System
The national system is currently experiencing changes as Tasmania, South Australia, and rural Victoria is replacing their shielded route numbering system, which was used in the past and now using alphanumeric style. Before 1995, the route marking used for the National system was in two major tiers. These were;
The National Route System
This consisted of the major interstate highways in the country, and all the roads within the system were marked with a black and white shield that is shaped like the shield on the Australian Coat of Arms. The introduction of this system was in 1954, and every new route after that time has been marked with the sign to create a complete. Austroads, then known as COSTA (Conference of State Road Authorities), prepared the system. It drafted the initial plan and also managed the system as the National Association of Australian State Road Authorities (NAASRA) till the 1980s. The National Highway system is related to the National Routes and refers to a collection of highways that are funded by the federal government. These highways are the most favourable roads linking capital cities (plus Burnie and Cairns). You can tell this road by the marked with a green and gold shield that is shaped like the shield on the Australian Coat of Arms. The National Route system numbering style is also used here, and it links with it.
These refer to the state routes in every state except Tasmania. The roads are marked with blue shields, and they include major intrastate and urban links. It also includes the Tourist Drive that has brown shields, and motorists can use it to get into tourist destinations that are recognised.
The new route marking style is now being used on Australian highways. It is an alphanumeric style which is what is being used in several parts of Europe and Britain. Australia adopted it in May 1997 after an agreement between all the federal and state transport ministers that there should be a consistent route numbering approach. Since then, many states have already installed it, and others are expected to follow suit as well. You can check out the progress of the adoption here.