 Route markers were first introduced in Australia in late 1954 . Over the following decades they were progressively rolled out to the various highways around the nation , under a nationwide route numbering scheme . The highway originally carried the National Route 23 route marker . Although after the construction of the Eastern Parkway extension , the highway north of Canberra Avenue was signed with the Alternate National Route 23 route marker . The section of the Monaro Highway between Steeple Flat and Cooma was also signed the National Route 18 shield in addition to the National Route 23 route marker used along the remainder of its length ; this kind of arrangement is known as a concurrency . This allowed one route to cover the Snowy Mountains Highway from end to end , as the Monaro Highway forms a link between that highway 's two sections . 
