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. The
North-Western Highway was declared (as Main Road No. 7) on 8 August 1928, from the interchange with
Great Western Highway and
Mid-Western Highway in Bathurst, via Orange, Dubbo, Nyngan, and Bourke, to the border with Queensland; to provide for additional declarations of State Highways and Trunk Roads, this was amended to State Highway 7 on 8 April 1929. On 9 October 1936 the name was changed to the Mitchell Highway, in honour of
Lieutenant Colonel Sir Thomas Mitchell, who was
Surveyor-General of New South Wales in the 1820s and explored much of inland New South Wales,
Victoria and Queensland. The passing of the
Roads Act of 1993 updated road classifications and the way they could be declared within New South Wales. Under this act, Mitchell Highway today retains its declaration as Highway 71, from the state border with Queensland at Barringun to the intersection with Great Western and Mid-Western Highways at Bathurst. Mitchel Highway was signed National Route 71 between Augathella and Nygan, and National Route 32 between Nyngan and Bathurst, in 1955. With both states' conversion to their newer alphanumeric systems in 2004 and 2013, its former route numbers were updated to Alternative A2 between Augathella and Charleville and A71 between Charleville and the state border within Queensland in 2004, and B71 between the state border and Nyngan and A32 between Nyngan and Bathurst within New South Wales in 2013. In November 1972 the last section of the highway was sealed.
Truck explosion On 5 September 2014, a truck travelling on Mitchell Highway rolled off a road bridge at Angellala Creek approximately 30 km south of Charleville (). The truck was carrying 52 tonnes of
ammonium nitrate which exploded. The blast destroyed the two road bridges and severely damaged the adjacent rail bridge. The blast was so powerful that the truck was disintegrated and the dangers posed by the remaining ammonium nitrate necessitated a 2 km exclusion zone around the site for a number of days. The large crater formed by the blast closed the highway necessitating detours of up to 600 km. The
Department of Transport & Main Roads was allowed to commence work at the site on 13 September and by 23 September had constructed a temporary side track around the blast site suitable for cars, buses and light trucks. By 7 October, the side track had been upgraded to support road trains, ending the need to detour. In April 2015, the $10 million tender to reconstruct the highway and bridges were awarded and the construction work took place between June and November 2015. In early 2016, a competition was held to decide a new name for the bridge. ==Major intersections==