State Highway No. 7 was declared on 8 August 1928 and named North Western Highway . This name reflected its role as a fork of the Great Western Highway (the other fork being the Mid Western Highway ), which ends at Bathurst . However, the name was changed to Mitchell Highway on 9 October 1936 , to honour Surveyor-General Thomas Livingstone Mitchell who explored the area which the highway serves in 1845.

Early work on the highway was justifiably concentrated at its south-eastern end, serving the more closely spaced settlements. Transport of produce from the vast cattle stations toward the north-western end of the highway was done by rail and, for many years, the Mitchell Highway remained just a barely-formed road alongside the railway line.

By mid-1958 the bituminous seal had been extended as far north as Nyngan, at the junction with the Barrier Highway , however north of Nyngan over 320km of the highway remained to be surfaced. A dust-free pavement had been provided only on a 13-mile section at Bourke (2km south to 10km north of Bourke) and for short distances through the towns of Coolabah, Byrock, Enngonia and Barringun. Over the next three years, from 1958 to 1961, the Department of Main Roads’ works organisation at Bourke extended the length of bitumen either side of town by 16 miles (i.e. 14mi south to 15mi north of Bourke).

In 1961 the Department of Main Roads established a works office at Nyngan, whose efforts were concentrated on the completion of sealing between Nyngan and Bourke. With a rate of 20.5 miles (~32km) of bituminous sealing per year, this target was achieved in mid-1966. This meant that the Mitchell Highway had a dust-free pavement from Bathurst to Bourke, a distance of 576km.

North of Bourke, the sealed pavement was extended a further 5 miles during 1961/62. In 1965, reconstruction work was commenced on the black soil areas, which were regularly impassable, between Enngonia and Barringun and this 21-mile section was completed in 1968. The missing link, from 20 miles north of Bourke to Enngonia, a distance of approximately 68km, was completed with much rejoicing on 6 November 1972 . Thus the Mitchell Highway had been provided with a dust-free surface for its entire length in New South Wales .

However, the black soils plains weren’t the only obstacle to road building on the Mitchell Highway . During the first half of 1971 floods caused extensive damage to the Mitchell Highway between Molong and Dubbo. With the damage not as bad as other areas of the state, repairs were carried out promptly and the roads returned to good condition.

Following the cessation of flood repairs, work was able to continue on improvements tot eh highway between Bathurst and Dubbo. The centrepiece of pre-1971 work was a new pre-stressed concrete bridge over the Macquarie River in Dubbo, which replaced a narrow timber truss bridge that had been in service since March 1905. The bridge was vital to the Dubbo community, being the only crossing of the river in town and carrying through traffic from both the Mitchell and Newell Highways. At the time, it was also the fourth longest road bridge in New South Wales . The old bridge was demolished after opening of the new bridge.

During 1972, around the time that bituminous sealing of the highway was completed further north, the Department of Main Roads was reconstructing sections of the highway near Molong and between Bathurst and Orange . A 6-mile section of the highway north of Molong contained four bridges, two of them over the Bell River, which is part of a realignment and widening programme to provide a 24 feet (~8m) wide pavement on the highway.

Extensive flooding on the Macquarie and Bogan rivers reared its ugly head again at the end of the 1980s. Whilst the bridge over the Macquarie River and flood plain at Dubbo was safe, the timber bridge over the same river at Wellington , which had been in service since 1920, collapsed under the force of raging floodwaters and debris. Temporary bailey bridging was installed as soon as floodwaters subsided to re-open the highway until a more permanent structure could be built. The new bridge, a concrete structure, was opened to traffic in December 1991.

At Nyngan, flooding of the Bogan River severed the highway for weeks during April 1990, causing severe damage to the three existing bridges over the river and flood plain. Unlike the aforementioned bridge at Wellington , these structures did not collapse, however they were subject to load limits until new bridges could be built. Three new concrete structures were built, with clearance above April 1990’s record floods. The two bridges over the flood plain were opened first, in June 1992, with the structure over the main river channel following in June 1993.

Just north of Bourke, the Darling River was crossed by an old steel bridge with a bascule lift span that had been in service since 1878. Having been in service for such a long time, the bridge was becoming structurally deficient and major rehabilitation was needed to keep the bridge in service. Instead it was decided to build new structures to carry the highway over the Darling River and flood plain, as this would remove the height limit imposed by the old bridge’s overhead trusses, and would open the Mitchell Highway up to higher mass limits. The new bridge over the main channel of the river was named ‘ Gateway Bridge ” upon opening in September 1997.

During the early 21 st century, under its Roads of National Importance programme, the Federal Government funded the construction of several overtaking lanes on the Mitchell Highway between Bathurst and Orange to improve travelling conditions on a section of highway carrying ever-increasing traffic volumes.

There have been calls for the construction of a bypass of Orange , however there has been no official agenda set. A reservation for a bypass on the northern side of Orange does exist, having been selected by the Department of Main Roads in June 1973 and consequently included in the local planning scheme. An earlier traffic relief route was selected in 1955 by the Department of Main Roads and endorsed by Orange City Council, however it was not long before both the DMR and Council realised that the line had unsatisfactory features, particularly regarding the use of Woodward Street . Consequently, in conjunction with the preparation of the Orange Town Planning Scheme in the early 1970s, investigations were undertaken to find a new line for a bypass. The selected route leaves the Mitchell Highway at Chinamans Bend, east of Orange , and passes to the north of town, with a connection to the CBD via Hill Street , thence rejoining the Mitchell Highway north of Escort Way . A continuation of the bypass to a realigned Escort Way (SR90) was also included. Following the selection of the reservation, it was proclaimed a motorway, so to prevent any development from occurring which might interfere with the movement of motor traffic.

Elsewhere, the heavy truck traffic which uses the highway has been routed around the commercial centres of Narromine and Nyngan for some time. The latter has in fact become the signposted route of the Mitchell Highway , I believe some time during the mid 1990s, replacing the former route of Pangee St and Hoskins St, however it is possible that it was done in conjunction with the opening of the new bridges over the Bogan River and flood plain.