I would like to know if there is a specific clause/regulation in the South African Road Traffic Act or South African rules of the road manual that states making a u-turn on a highway is illegal?
Reg 297 applies
Driving on divided public road
(1) Whenever any public road has been divided into two or more roadways
by means of an intervening space or by a physical barrier or dividing section so constructed as to impede vehicular traffic, no person shall drive a vehicle upon such public road except upon the left hand roadway, unless directed or permitted by an appropriate road traffic sign or a traffic officer to use another roadway.
(2) No person shall drive a vehicle on, over, across or within any
dividing space, barrier or section referred to in subregulation (1), except through a constructed intersection: Provided that no person shall so drive through such constructed intersection where such driving is prohibited by an appropriate road traffic sign or by a traffic officer: Provided further that the provisions of this subregulation shall not apply to a traffic officer in the performance of his or her duties.