Eric Carson (1913–99), a Gloucester sawmiller and road builder, carved the first road through the ranges to bring out the magnificent hardwood from the forests on the Great Divide. After Carson spent many years trying to persuade local politicians that a road should be built across the Divide from Gloucester to
Nowendoc, he went ahead and built it. Carving the route out of some of the steepest and most rugged countryside in the state was fraught with danger, but by 1961 it was complete. Carson's Lookout, which commemorates his work is between Gloucester and Nowendoc, is a stop off point for the enjoyment of panoramic views. 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 (MRB, later
Transport for NSW). Main Road No. 115 was declared from the intersection with
Oxley Highway in Walcha, via Uralla, Balala, Bundarra and Gilgai to the intersection with
Gwydir Highway at Inverell, to provide for additional declarations of State Highways and Trunk Roads, this was amended to Main Roads 115 and 122 and 124 on 8 April 1929. The
Department of Main Roads, which had succeeded the MRB in 1932, declared Trunk Road 73 on 11 December 1934, from the intersection with
Gwydir Highway at Inverell via Gilgai, Bundarra, Yarrowyck and Uralla to the intersection with
Oxley Highway, subsuming the former alignments of Main Road 115 (between Inverell and Bundarra, and Uralla and Walcha; the former route between Bundarra and Uralla via Balala was removed) and Main Road 122; the western end of Main Road 124 was truncated to meet Trunk Road 73 at Yarrowyck. by
Guyra Shire between Copes Creek (30km south of Inverell) and Bundarra on 19 August 1991; and by
Uralla Shire between Bundarra and Walcha on 21 December 1991. The portion of Trunk Road 73 within
Inverell Shire (between Inverell and Copes Creek) is still known by its original name, Bundarra Road. 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, Thunderbolts Way today retains its declaration as Main Road 73, from Inverell to Walcha. The road from Walcha to Gloucester has been since classified as Regional Road 7719. ==Major junctions==