The third section was the most technically demanding, as it ran through heavily built-up urban areas and required numerous properties to be demolished, along with the "Thirteen-arch viaduct" near Stapleton Road that was built in 1874. Work was delayed owing to the Three-Day Week industrial action in 1974, and further because of a national builders' strike. During construction, the Local Government Act 1972 was passed, and responsibility passed to the newly created Avon County Council in April 1974. This section, and hence the full extent of the motorway, was opened to traffic in May 1975. The cost was reported to be £10.4 million (now £ million).