Snowy Mountains Highway is a
History
250px|thumbnail|Snowy Mountains highway near [[Kiandra]]
The passing of the Main Roads Act of 1924 through the Parliament of New South Wales provided for the declaration of Main Roads, roads partially funded by the State government through the Main Roads Board (later Transport for NSW). Monaro Highway was declared (as Main Road No. 4) on 8 August 1928, heading northwest from Tathra, via Bega, Nimmitabel, Cooma, Adaminaby, Tumut, Adelong, and Lower Tarcutta to Wagga Wagga. to provide for additional declarations of State Highways and Trunk Roads, this was amended to State Highway 4 on 8 April 1929.
The Department of Main Roads, which had succeeded the MRB in the previous year, proclaimed the portion of the highway between Wagga Wagga and Hume Highway at Lower Tarcutta to be part of Sturt Highway on 8 August 1933; the highway's western end was truncated at its own junction with Hume Highway near Hillas Creek instead.
When the Snowy Mountains Scheme commenced in 1949, the road began to increase in importance. Roadworks to increase the standard of the road were undertaken, and were often paid for by the [[Snowy Hydro|Snowy Mountains
Hydro-Electric Authority]]. This was done as only a relatively small portion of the road was actually within the Monaro region. The section of road between Cooma and Nimmitabel was also reclassified as part of State Highway 19, which at that time ran from Canberra, to the Victorian border west of . The various roads classified as State Highway 19, were then named as Monaro Highway in 1958. In contrast with Snowy Mountains Highway, the entire length of that highway is within the Monaro region.
Over the years further changes to the alignment have occurred. The eastern section of the highway no longer runs west to Nimmitabel, instead meeting Monaro Highway to the south; the old section has been renamed as Old Bega Road. The western section has also seen some major changes with the highway being realigned to avoid Lake Eucumbene near Adaminaby due to the construction of Eucumbene Dam in the 1950s. Similarly realignment was required to avoid the Jounama Pondage and Blowering Reservoir near due to the construction of Jounama and Blowering Dams in the 1960s.
The passing of the Roads Act of 1993 through the Parliament of New South Wales updated road classifications and the way they could be declared within New South Wales. Under this act, the eastern end of the highway was truncated to the intersection with Princes Highway at Stony Creek north of Bega on 24 May 1996; the former section from Bega to Tathra was renamed as Tathra Road.
Route markers
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, with the highway allocated National Route 18 across its entire length in 1955. In addition to this, the section of Monaro Highway between Cooma and Steeple Flat was also signed as National Route 18 in addition to the National Route 23 route marker used along the remainder of its length within NSW; this kind of arrangement is known as a duplex or concurrency. This allowed one route to cover the highway from end to end. With the conversion to the newer alphanumeric system in 2013, this was replaced with route B72. The concurrency along Monaro Highway remains intact with B72 used in addition to B23 between Cooma and Steeple Flat.