Early roads 's 1834 map(Note: Top of image is roughly northwest) A minor road appeared in this region on
Thomas Mitchell's 1834 map of the
Nineteen Counties of New South Wales. Located within
Murray county, the road continued from towards the south before turning west crossing the
Queanbeyan River near its confluence with the
Molonglo River (the current location of ), which then headed south towards what was then known as the "Miccaligo Plains" (now ). The road is then marked as continuing south beyond the border of the county; although no settlement could legally occur beyond the Nineteen Counties at that time, those who settled beyond this area were known as
squatters. The detail of the road beyond Murray county is not plotted on the map. By 1844 the road had reached
Cooma, and was extended to Bombala by 1852. Mapping from 1882 shows the road had extended all the way to the Victorian border, crossing near .
Highway Victoria Within Victoria, the passing of the
Country Roads Act 1912 through the
Parliament of Victoria provided for the establishment of the
Country Roads Board (later
VicRoads) and their ability to declare Main Roads, taking responsibility for the management, construction and care of the state's major roads from local municipalities.
Cann Valley Road was declared a Main Road from
Cann River to the border with New South Wales on 23 March 1914. through the Parliament of Victoria allowed the Country Road Board to declare Developmental Roads, serving to develop any area of land by providing access to a railway station for primary producers. Cann Valley Road was subsequently reclassified as a Developmental Road on 14 January 1920. The passing of the
Highways and Vehicles Act 1924 provided for the declaration of State Highways, roads two-thirds financed by the state government through the Country Roads Board.
Cann Valley Highway was declared a State Highway on 10 August 1960, from
Cann River to the border with New South Wales (for a total of 27.5 miles), subsuming the original declaration of Cann Valley Road as a Developmental Road. As part of the
Bicentennial Road Development Programme, the roadway was sealed along its entire length, the project being completed in March 1985. It was renamed
Monaro Highway on 25 October 1996, to match the highway to which it connects at the NSW border. The passing of the
Road Management Act 2004 granted the responsibility of overall management and development of Victoria's major arterial roads to
VicRoads: in 2004, VicRoads re-declared the road as Monaro Highway (Arterial #6760), beginning at
Cann River and ending at the New South Wales border in Chandlers Creek.
New South Wales The passing of the
Main Roads Act 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), to provide for the additional declarations of State Highways and Trunk Roads. The roads forming the future highway were given the following classifications on 8 August 1928: The
Department of Main Roads, which had succeeded the New South Wales MRB in 1932, declared State Highway 19 on 16 March 1938, from Canberra via Royalla and Bredbo to the intersection with State Highway 4 at Cooma, and from the intersection with State Highway 4 at Nimmitabel via Bombala and Delegate to connect with
Bonang Highway at the state border with Victoria, subsuming Trunk Road 53; the section of State Highway 4 between Nimmitabel and Cooma was also re-designated part of State Highway 19 at the same time. In contrast with Snowy Mountains Highway, the entire length of State Highway 19 was within the Monaro region. During the mid to late 1960s the highway south of Nimmitabel was rerouted along a newly constructed roadway; the former alignment is now known as Old Bombala Road. The alignment of the highway's southern end to the state border with Victoria was later changed, travelling via Rockton to connect to Cann River Highway, instead of via Delegate to connect to Bonang Highway, on 12 October 1977; the former alignment was proclaimed Trunk Road 93 and is now known as Delegate Road. through the
Parliament of New South Wales updated road classifications and the way they could be declared within New South Wales. Under this act, Monaro Highway today retains its declaration as Highway 19, from the state border with Victoria via Bombala, Nimmitabel, Cooma and Michelago to the state border with the Australian Capital Territory.
Australian Capital Territory In 1958 Federal government agreed rename the Cooma-Canberra Road within the ACT as Monaro Highway: this gave the roadway a single name between Canberra and the Victorian border. Originally, the highway ended where it met Jerrabomberra Avenue. Plans were publicised during the mid-1980s for an upgrade of the existing Monaro Highway to dual-carriageway standard between Isabella Drive and Jerrabomberra Avenue, and an extension of the roadway to the north. These works were known as the Eastern Parkway. These plans were then given the go ahead in a report tabled on 5 May 1987, the estimated costs were $50 million including upgrades to other nearby roadways. Around the same time period a large service centre was proposed for near the Isabella Drive intersection, though it was quite controversial, and the developer pulled out. Between 1988 and November 1989 the duplication was completed, and the roadway extended as far as
Canberra Avenue. After this the road was extended to its current terminus at Morshead Drive, although the northbound carriageway was originally routed over Dairy Flat Road until a southbound carriageway was constructed later on. Further duplication was performed to other sections of the extension until all sections were completed in mid-2012. The northern end of Monaro Highway now connects to the southern end of
Majura Parkway following the latter's completion in 2016.
Territory and Municipal Services has classified Monaro Highway as an arterial road within the ACT Road Hierarchy. Currently, upgrades are underway to the highway near Hume, providing new grade separated interchanged at Lanyon Drive and Isabella Drive, as well as
left-in, left-out intersections with Mugga Lane, Tralee Street with an overpass between these intersections. The upgrades will complete a 25 km long
motorway-standard road all along eastern edge of Canberra.
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. The highway was originally designated National Route 23 in 1962 between Canberra and Cooma, extended further to Nimmitabel in 1967. Although after the construction of the Eastern Parkway extension, the highway north of Canberra Avenue was designated Alternate National Route 23. With all three states' conversion to their newer alphanumeric systems between the late 1990s to the early 2010s, its former route number was updated to route B23 for the highway within Victoria (in 1997), to route B23 within New South Wales section (in 2013), and route A23 within the Australian Capital Territory (also in 2013). This violates the convention in New South Wales, where numbered routes below 50 are prefixed with an 'A' and 'B' routes are numbered above 50; the violation was allowed so the number and letter would be consistent across state lines. The concurrency along Monaro Highway remains intact, with B72 used in addition to B23 between Steeple Flat and Cooma, linking the two sections of
Snowy Mountains Highway. In the ACT, Monaro Highway is designated route A23 from the NSW border to Canberra Avenue, and as route M23 north of Canberra Avenue to its terminus, where it joins
Majura Parkway. ==Junctions==